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tim53
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Delmarvascopics 8" f/9 OTA build
      #5285595 - 06/23/12 04:43 PM

Okay, it's time!!!

I finished this mirror at the Delmarva mirror class in March 2011, got it coated by L&L about a year ago, and it's been sitting in my drawer for about a year now. I NEED to make another mirror, so I have to get this one done so I can make room for the next project!

The mirror started life as a Telescopics kit, with pyrex tapered blank and ceramic tool, that I bought about 39 years ago! I started grinding it, intending to make an f/9 from the get-go, since I already had the Optical Craftsmen 8" f/6 Discoverer that I'd bought the year before.

Anyway, finished the mirror, finally, at the mirror class last year. If I may say so myself, the mirror tested out on Dick Parker's autocollimation rig as damned bitchen', so I'm anxious to siphon some planetary photons down with it.

So, for a tube this time, this is what I was thinking: Something that would interchange with the tube on my Optical Craftsmen 8" f/6.3 Connoisseur mount. But I didn't want to have to pay arms, legs, and other perhaps more precious appendages for a fiberglass tube. So, I decided to try to make a round tube all by my ownsome.

Last weekend, I experimented with rolling up thin plywood sheets that came as packing material with a bunch of garden chairs we bought a few years back. This stuff is about 2mm thick, so after wetting and letting it sit in the sun for about a half hour, it wasn't that hard to roll up to fit inside a 5" cardboard shipping tube I had layin' around.

Here is the result after I took it out of the tube:

Edited by tim53 (06/23/12 04:48 PM)


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285598 - 06/23/12 04:45 PM Attachment (188 downloads)

I hate Apple's new preview application. The old one displayed what you got - rotated the RIGHT WAY UP like I saw on my bloody screen! One more time!

Edited by tim53 (06/23/12 04:47 PM)


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285607 - 06/23/12 04:49 PM Attachment (120 downloads)

Sorry about that...

Next, I got all cocky and thought I could just as easily roll up a full 4x8 sheet of 2.7mm Home Despot plywood. Here's the first squeeze:


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285608 - 06/23/12 04:50 PM Attachment (103 downloads)

2nd squeeze

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285619 - 06/23/12 04:58 PM

Now that I think I can actually roll this stuff up into a 9 3/4" cylinder, I'd better get out there and make me a set of forms to wrap it around!

I figured i'd make innies and outies. the innies would be removed after the tube is done, as I'm not one of those dudes who likes baffles in my Newtonians. Most of the outies, I figure, will be round inside and square outside, to hold the outside shape as I staple the plywood to the innies. A few (four?) of the outies will be rings that I'll permanently attach to the tube. Two of these will be end rings and two will be the fixed halves of the rotating rings that will work with the mount's rings. I realize as I type this that these rings will have to be removable so they can be adjustable. It probably makes sense to make the end rings in a similar fasion, then. That way, I won't have to cut off the square form rings to free up the tube when I'm done.

I've only got two Rockler strap clamps here, but I bet I can get by with some cheaper hold down straps from Home Despot. We'll see.

I'm off! let's see how successful I am! I've only got ten bucks invested in the plywood, so if this doesn't work, I won't cry much or for long.

-Tim.

Edited by tim53 (06/23/12 05:01 PM)


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285670 - 06/23/12 05:38 PM Attachment (84 downloads)

3rd squeeze...

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285674 - 06/23/12 05:39 PM Attachment (95 downloads)

Houston? We've had a problem...

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285689 - 06/23/12 05:48 PM

Gonna have to get the garden hose out for the next squeeze!

-Tim


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tcmzodiac
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285704 - 06/23/12 05:55 PM

You are the best, I love your posts and knowledge! And chutzpa...

(in a tiny voice may I ask) Would going for a pre-made tube..maybe a Protostar...be out of the question???
(duck and cover)


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tcmzodiac]
      #5285759 - 06/23/12 06:38 PM Attachment (78 downloads)

Hi Terry. Try not to laugh TOO hard! You're the wood expert, after all. I do have a luthier friend down the street who's kind of "interested" in how I do, but I think he's laughing inside as well.

Protostar, plywood columns, fiberglass = all expensive. If I succeed, and that's a BIG IF, I'll only have 10 or 20 bucks invested in this tube. Well, and a whole herd of time!

I thought I was a gonner when this happened, though:


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285760 - 06/23/12 06:39 PM Attachment (66 downloads)

But it turns out, it's less than 18" from the edge. I only need about 30" or so to make a 9 3/4" OD tube, so I'll keep trying with this and see if I can make it without splitting it where I need it to stay intact.

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5285811 - 06/23/12 07:31 PM

Well, rats. I thought I'd make the outie forms first, but my circle jig for my router doesn't go small enough to make 9 3/4" circles.

So, I'll have to make something out of scrap, or start with the innies, which I could cut on the band saw.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5286909 - 06/24/12 02:53 PM Attachment (64 downloads)

New day, new problems...

Well, not something I didn't think might happen, but here's what I was trying to achieve:

This is the thin stuff I rolled up last weekend, sitting inside a couple of the 8 "outie" forms I made with scrap 18mm Home Despot Ecuadorian plywood left over from that shelf unit project I'm building upstairs. I have enough of this stuff to make a two-layer tube in 2-foot long segments to bold together. But I'll need an innie form to do it - otherwise the layers will not be tight.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5286914 - 06/24/12 02:55 PM Attachment (50 downloads)

Here, I've just put one of the round cutouts left over from making the outie forms on the inside to see if they'd serve to accomplish this. But they're too small (router bit width and all):

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5286937 - 06/24/12 03:06 PM

Rockler has veneers available in 2x8' sheets, but the grain appears to run across the width rather than parallel to the length, so wouldn't be optimal unless I wanted to make a multi-part tube or paint it. And then, the price would be ridiculous to get enough strength that way (I think they were upwards of 80 bucks per 2x8 sheet, and so I'd need several to make a tube).

This is all getting a bit too Rube Goldberg even for me!

So, I think I'm going to fall back on my tried and true method of making faceted tubes. I don't have a sheet of plywood to use, so I'm either going to have to go get one, or go ahead and use the beautiful 2x6 Cherry stick I bought last year for this project. It's only 5 and a half feet long, so I'll likely need to add a "dew/lightsheild to the end, and/or mount the mirror cell onto the end of the tube so the mirror surface isn't far inside the tube (great for cooling anyway) like I did for the 10" Delmarvascope:



...since the Fl for the 8" is 6 feet.

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287145 - 06/24/12 05:53 PM

I hate it! LOL!

Well, I may have wasted the whole weekend on this stuff. I suppose if I were to use the thin plywood pieces that I have, I could make a full length tube by putting the sections together while I'm laying on the 2nd layer of plywood and overlapping them over the joints between two sections. Would have to paint it, of course.

But although I've spent little money on this, I've burned a ton of time. I should either go ahead and make a polygonal tube out of 1/4" plywood (fastest method of making a tube I've ever come up with), or just order a plywood column from Anderson, an aluminum tube from Hastings, or a fiberglass tube from Parks.

Like I said, the hardest part about a polygonal tube is adding rotating rings to it. For my Springfield, the Cass, and the Jaegers 6" f/15, this wasn't a problem because the tubes don't rotate.

Anyway, before the day is over, I'm going to put this project away and work on something else that needs to be done - clean up my workshop!

-Tim.


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amicus sidera
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287223 - 06/24/12 06:49 PM

Tim, don't forget these folks:

Precision Paper Tube Company

High-strength phenolic-impregnated tubes, perfect for telescopes - those made from Resinite RS-8717 would be the best, IMO; extremely strong, fairly lightweight and dimensionally stable - easily sawn and drilled, too. Edmund used almost identical tubing for all their reflectors from '78 onwards, and judging from the examples I've seen they've held up very well over the years


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287230 - 06/24/12 06:52 PM

Quote:

Rockler has veneers available in 2x8' sheets, but the grain appears to run across the width rather than parallel to the length




what makes you say that? I never saw the grain run the 2' and always run the 8'. was that they're allwood veneer which is two different woods?

I'd buy their 3'x8' paper back veneer and expoy several layers.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: amicus sidera]
      #5287239 - 06/24/12 06:59 PM

Thanks for the link! Any idea how expensive? I'm surprised at the prices I'm seeing for fiberglass, aluminum, and blacklight (which needs to be spliced for longer than 48" lengths).

Oddly, the cheapest I've seen so far is the plywood columns for $218 for an 8' length of 10" OD and 5/16" wall.

-Tim.


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amicus sidera
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287253 - 06/24/12 07:08 PM

Tim, I got a ballpark estimate from them back last winter when I was interested in getting a replacement tube for my Edmund 6" f/6 (the one in my avatar) - due to the end cells on these and the Edmund 8" f/5, a tube with a specific i.d./o.d. is required. The ballpark figures: setup charge for the machinery is about $100, with the approximately 7" diameter, 36" long and 1/8" thick wall tubes costing about the same, $100 each, with a price break after quantities of ten (!). These are made from Kraft paper layered with the phenolic resin specified, spiral-wound, then baked to cure and cut to exact length. Light brown in color as they come to you, easily primed and painted (make sure to specify that they will be painted, to prevent application of wax or other protectant).

Also, no need to line these babies with cork or other insulation... they're very thermally-stable.

Edited by amicus sidera (06/24/12 07:17 PM)


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Blast420
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287280 - 06/24/12 07:23 PM

It would cost me about $40-$100 to make a fiberglass tube in the 6” to 12” range up to about 6’ in length, thats not including the gelcoat which adds about another $10-$20.

Edited by Blast420 (06/24/12 07:23 PM)


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Mirzam
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287980 - 06/25/12 07:56 AM

I know that some people have used these:

http://www.yazoomills.com/mailing-tubes/heavy-duty-kraft.aspx

JimC


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #5288382 - 06/25/12 01:00 PM

That looks like the source for the blue paper tube I used to roll the thin plywood up in. I've left that tube outside in the rain, and although it started blistering at the bottom end, it dried out okay and is still fine.

Prices seem reasonable, too. But I think I'd want to use a low-viscosity epoxy to stiffen it and protect it some, like Abatron's liquid wood that I use for home repairs and stuff.

-Tim.


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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5288401 - 06/25/12 01:10 PM Attachment (37 downloads)

that yazoomills tube is what I used for my stellafane rip off...
still need to paint the tube in a catalyzed poly, that stuff can make bullets bounce off of it.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5288578 - 06/25/12 03:04 PM

Good suggestion! Where do you get the catalyzed polyurethane?

-Tim.


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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5288767 - 06/25/12 04:53 PM

I use an automotive clear topcoat that has to be mixed 100 parts poly 50 parts hardener. the clear is a high solids.

I use sikkens paint they've changed their product name several times over the years.

this is similar, not the same but very similar.


http://www.ebay.com/itm/Qt-High-Gloss-2K-Acrylic-PolyUrethane-Urethane-Clear-Coat-Clearcoat-Paint-Kit-/271003558006?pt=Motors_Automotive_Tools&hash=item3f19122076&vxp=mtr


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5288914 - 06/25/12 06:31 PM

Wow, that's really reasonable!

How well would it penetrate the paper, I wonder?

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5288988 - 06/25/12 07:33 PM

well I'm going to gel coat the tube as a primer with a typical lacquer primer and put a color base coat before I clear coat the tube.

I don't know about penetrating but it will adhere very well. you have to wait 24hours before you sand between coats with my sikkens.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5296394 - 06/30/12 01:51 PM Attachment (36 downloads)

Okay, do over!!

I decided to continue this thread rather than start another one, as I'm not ashamed to admit when I've done something stupid or tried something that doesn't work...

So, I decided to use that 5.5' 2x6 of beautiful grain cherry that I bought about a year ago for a scope project. Since it's only 5 1/2 feet long, I plan to make a removable dewshield and/or a removable primary mirror box/cell, since the FL of the mirror is 72".

Also, since I had already made forms to roll plywood up inside that are 9 3/4" ID, I decided to use them to control the cylindricity of the faceted tube. HOWEVER, my traditional 9-sided tube won't work, since the insides of the facets would be too close to the optical path (about 0.06"). So, I played with the polygon calculator Poly and came up with a 20-sided tube with 1.5" sides as my best option.

Here are the sides, all cut up and thickness planed smooth. Next I'll trim them to width and bevel the edges. I could use a cooper's bit set that I have, but I think that would take longer to set up than simply angling the table saw blade.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296404 - 06/30/12 01:58 PM Attachment (38 downloads)

The slats are all bookmatched, so the grain more or less continues from one slat to the next, but of course there will be missing gaps from the saw kerf when I cut the bevels and the slats to width.

Here are all the forms I made last week, plus some lazy susan bearings I bought online to make rotating rings (very reasonably priced, compared to "real" rotating rings from Parks or Parallax, but they'll need reinforcment rings of plywood to control flexure). The site where I got these doesn't list the ID for the larger sizes, only the OD. So, I was pleasantly surprised to find that they're maybe a millimeter under 9.75" ID.

The smaller ring is one that I added to the order to try for other things, and since it's about 3.5" ID, I think I might use it as part of a rotating focuser mechanism. I still haven't decided on my focsuer. Probably a sled (with the rotator incorporated, perhaps). But I've also been cogitating about building the mirror box something like a Clement focuser body, where the mirror cell is mounted to the moving part of the "focuser". Then, I could call my eyepiece holder a "no-profile focuser" or something! Of course, it'll have some profile. But I'm not sure how feasible it will be to make a moving primary cell that maintains alignment.

I'm not likely to finish this weekend anyway. But it'll be nice to lay up the tube at least.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296411 - 06/30/12 02:01 PM

For putting the tube together, I was planning on doing something like I've always done - where I use a boatload of painter's masking tape to tape up the sides into a venetian blind, turn them over and squeeze glue into the grooves between slats, roll the whole thing up, and put it in the forms?

If I do it that way (or even if I lay one side in the forms at a time), I plan to cut one side of the forms so I can expand them to take the rolled up tube, then put clams across the gap and squeeze the tube together and hold it round while the glue dries.

Thoughts?

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296416 - 06/30/12 02:03 PM

Oh, and the lazy susan bearings were $15 for each of the big ones and under $8 for the small one.

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296420 - 06/30/12 02:04 PM

Back to work!

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Jeff Morgan
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296556 - 06/30/12 03:38 PM Attachment (41 downloads)

Just getting up to speed on your thread Tim. I'll bet your f/9 is going to be killer. When people try to pigeonhole these as "planetary" scopes, they're missing something very important - a scope that is great on planets will be great on anything!

As to the tube construction, I would also go strip plank, or possibly octagonal. The issue there being how accurately one can make long cuts at the required 22.5 degree angle. I wouldn't want any gaps in the joint over the length. (I have enough trouble making 45 degree miters work!) One possible approach to cover that would be to do a hardwood inlay down the length of the joint. I'm doing this on my current project. It uses very thin (1/16" plywood) which is next to impossible to get clean joints with. So I cut away the edges on a router table and laid in a mahogany strips and sanded it all flush (photo attached of the piece in progress - note the edges.)

I'm not familiar with Coopers bits - would you be referring to bead & cove router bits? I have seen articles on this before, it seems rather straightforward work on a router table. Tack the strips to your forms (or better yet, use contrasting hardwood dowels) which can double as light baffles.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #5296586 - 06/30/12 03:59 PM Attachment (30 downloads)

Hi Jeff!

That looks pretty nice to me!

I've already cut all the bevels on the table saw. The chief reason for going with 20 sides is because I'd already made forms and the lazy susan bearings are just the right ID.

I just checked in my garage, and I need a LOT of painter's tape. So I think I'll make myself a sandwich and scarf some potato chips and head on over to Home Despot for a bunch of tape.

Fewer sides is better, from a truing standpoint. The steeper the angle, the better control on a straight tube.

I set up the forms on my 1960 VW singlecab pickup bed to see how things would go, but it's so hot and sunny right now that I think I'm going to have to do this on my garage floor.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296590 - 06/30/12 04:01 PM Attachment (40 downloads)

I cut kerfs in each form so I can clamp them tight around the tube while it dries. Also, I can wedge a screwdriver in to get them off the finished tube...

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296656 - 06/30/12 04:57 PM

Tim-
You're on your way to an amazing scope!!! 8" of aperture capable of high powers- wow!! And we all know that DelMarva mirrors are tops- the quality goes without saying!! Enjoying the thread, anxious to see the finished produce! What are you planning on doing on the inside of the tube??? I've used Yazoo tubes before/successfully- primered them inside/outside with thinned Poly varnish- then used flat black paint with a bucketfull of sawdust inside- dumped it/let it dry/rolled another coat of flat black over that... gave a wonderfully darkened tube inside.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Wes James]
      #5296695 - 06/30/12 05:36 PM

I'm planning on poly inside and out, followed by Rustoleum flat black inside, which I've had good results with before. I may add sawdust to it as well. I've sure made plenty of it!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296831 - 06/30/12 07:26 PM Attachment (28 downloads)

Okay, started taping the sides together!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296834 - 06/30/12 07:27 PM Attachment (35 downloads)

The trouble with having so many sides is that this method uses a LOT of tape. I think I went through about 2/3rds of a new roll:

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296835 - 06/30/12 07:28 PM Attachment (52 downloads)

I swear, one of these days I'm going to make a tube out of masking tape!!

I decided to check and make sure it would roll up all the way before I put any glue in the seams:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296840 - 06/30/12 07:29 PM Attachment (44 downloads)

And it's a darn good thing I did, because I was able to realize that the forms are too big (or the tube is too small):

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296845 - 06/30/12 07:35 PM Attachment (45 downloads)

Here it is in detail. the forms are 9 3/4" ID, like the lazy susan rings and standard Parks fiberglass tubes. And the tube sides are exactly 1 1/5" wide like the polygon calculator said they should be to get my desired OD. But the tube is about 9 5/8" OD, so it's sloppy in the forms. ID is about 9", so I'm only going to have a half inch outside the light path to the mirror. Good thing I didn't plan baffles!

All isn't lost, though. I figure if I cut a 3/4" gap in the forms, instead of the saw kerf width (about 1/8"), I can clamp it and it'll tighten all the way around the tube okay without breaking the forms. Another thing I could do, I suppose, is rip another slat, really narrow, to bring the tube diameter up to the desired OD. I don't have any more cherry, though. I might be able to find a strip of birch to use, but it'll be bright.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296914 - 06/30/12 08:30 PM Attachment (50 downloads)

I don't know how I manage, but I do! Here I have it all laid out for gluing. Now, that bottle of titebond III is only about 1/4 full. That's got to be enough, right? WRONG! I had to grab another bottle of titebond II I had laying around but couldn't get the top off, and in the middle of gluing up the slats, cut the top off the second bottle and used all of THAT glue too! Got 'er done, though! And then some. Natch, the glue ran out all over the inside of the tube once it was rolled up. I might scrape the worst of it off, but it might also be a good light-deadener with the black paint and all.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296916 - 06/30/12 08:31 PM Attachment (44 downloads)

Here it is rolled up and clamped in the forms:

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296920 - 06/30/12 08:33 PM Attachment (38 downloads)

Notice the gaggle of Harbor Freight clamps on the truck bed. Those are brand new clamps that DON'T WORK. I had to run around looking for clamps that did work!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296921 - 06/30/12 08:34 PM Attachment (38 downloads)

Glue running out on the inside. At least there must have been enough after all!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297135 - 06/30/12 11:43 PM Attachment (46 downloads)

Turned out pretty round!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297137 - 06/30/12 11:43 PM Attachment (48 downloads)

And straight!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297140 - 06/30/12 11:45 PM

And while I do like the look, cutting 20 sides, beveling them, and applying all that tape and glue really took a long time - maybe 4 hours?

Now, I've got to get myself rested up for another drive to Utah tomorrow. Guess I'd better check the craigslist ads between here and there, in case I need to make a stop or two along the way!


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297330 - 07/01/12 04:52 AM

A big glue up is stressful enough without the nightmare of poor clamps adding to it. Titebond III and its longer open time has saved my butt many a time.

That method of ripping strips off a plank produces wood with a rift sawn or quarter sawn figure. This makes for a much more stable product verses plain sawn lumber and it will look three times better to boot!

Four hours? You work fast!!!!!!


Edited by herrointment (07/01/12 05:23 AM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5297338 - 07/01/12 05:15 AM

Nice work Tim! I tried my hand at this with a 12 sided 12" o.d. tube without using forms. some of the strips moved a little, which required much sanding to correct. Next time I will use your method. That will look awesome when you are done! Keep us posted.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297342 - 07/01/12 05:31 AM

coolest thing i've ever seen! you really gotta love it don't ya?

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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5297842 - 07/01/12 12:46 PM

Quote:

A big glue up is stressful enough without the nightmare of poor clamps adding to it. Titebond III and its longer open time has saved my butt many a time.

That method of ripping strips off a plank produces wood with a rift sawn or quarter sawn figure. This makes for a much more stable product verses plain sawn lumber and it will look three times better to boot!

Four hours? You work fast!!!!!!





Actually, it's mostly face-grain. What I tried to do was make the cuts so that the grain would transition from one slat to the next. I started out trying to resaw the whole 6 1/2" plank on my bandsaw, but even with a carbide-toothed blade, the work wanted to wander off the line. I don't have a tall resaw fence, so was just using the stock fence (Rikon 18" saw), which can be set to accomodate the wander somewhat. But without going through a lot of good scrap wood trying to find the perfect setting angle for the fence, I had to guess, and my guess just didn't quite work out.

But since I was going to make such narrow slats anyway, I sliced the planks into 1 1/2" wide boards on the table saw, then resawed each board on the bandsaw - which prevented the wander since it wasn't such a thick stick to have to deal with. The bandsaw also saved wood, since the kerf is only about 1/16" wide, whereas the table saw "thin" blade takes out about 1/8" or so.

Anyway, if you were looking at the 2x6 from the end, I tried to number the slats in such a way that they were ordered from left to right, then zigging back the other way (and turning them on the second row to bookmatch them as much as possible), then zagging at the other end, an so on. I got 5 rows of slats that way out of the 2x6. Structurally, quarter sawing them would have been better, of course. And maybe I could have done that all on the bandsaw and saved stock.

Turns out, though, that I goofed in my numbering in a couple of places and beveled some slats in the wrong direction, so they were upside down with respect to the slats to either side. Oh well! It's still purdy!

After I took the tape off, I lowered a lazy susan bearing over the tube to make sure it fit without binding. And it not only does, but it's also just big enough not to. So the finished scope should look nice and "planned". The rings for my 10" f/6 are quite a bit larger than the tube (I wasn't aware that there were other sizes, and the next size down *might* have worked for the 10"). And I still haven't quite worked out all the little annoying points of flexure in them. The ones for the 8" will be easier to make good and stiff, I'm thinking.

Next weekend!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299002 - 07/02/12 08:04 AM

I can only imagine trying to do a glue-up like that!!
Wes


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299182 - 07/02/12 10:47 AM

Tim, how much does this tube WEIGH?!

Mladen

Edited by MKV (07/02/12 10:48 AM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: MKV]
      #5299248 - 07/02/12 11:42 AM

Hi Mladen:

I'm guessing, but I'd say about 1/3 the weight of a fiberglass tube, and a fair amount stiffer, too. Of course, I don't have any finish on it yet!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299261 - 07/02/12 11:47 AM

Hi wes:

To save time, I simply poured the glue onto the slats and used a wood paddle to spread it around and into the grooves. Turns out I had too much applied that way, but after it squeezed out during the rollup, I was okay. Better than not enough by a lot, too!

The masking tape works really well for this kind of rollup, because it pulls the two sides together quite well, and there's enough tape that it doesn't come apart under the tension. The bonus is that the tape helps keep glue from oozing out onto the outside of the tube and drying there. The tightbond 3 is waterproof, so it can't be washed off - has to be sanded off. I wasn't worried about it on this tube because the cherry is a closed grain wood. On mahogany it would have been a disaster. As it was, the glue on my 10" f/6 took a lot of scrubbing to get out of the grain where it wound up on the outside of the tube (but that was tightbond II).

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299301 - 07/02/12 03:30 PM

Tim-
I'm a big fan of masking tape in general in woodworking when it comes to glue-up's... Whenever I'm gluing a joint, I always mask it on both pieces, leaving only the glued surfaces exposed... I don't have to worry too much about applying excessive glue. Then, after I get it glued/clamped up, I wipe the excess glue squeeze-out off the tape thoroughly, then pull the tape- presto, a clean joint with no squeeze-out to worry about. Nice for natural finishes, necessary when staining!
Wes


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Wes James]
      #5299449 - 07/02/12 04:49 PM

That's a GREAT idea for getting the excess off the inside of the tube!

I'm going to try that next time I make one of these.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299538 - 07/02/12 05:56 PM

Quote:

That's a GREAT idea for getting the excess off the inside of the tube!

I'm going to try that next time I make one of these.

-Tim.




I thought you were going for the textured inside to help absorb the light.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5299697 - 07/02/12 07:44 PM

I did! (because I hadn't heard about taping the inside before I glued up this tube!)

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299704 - 07/02/12 07:45 PM

So here's another idea I've been cogitating...

Instead of a sled focuser, why not something like a Clement focuser - only not under the eyepiece, but under the primary!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5317860 - 07/14/12 06:07 PM Attachment (41 downloads)

Today, I squoze off some time to start sanding the tube:

Edited by tim53 (07/14/12 06:13 PM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5317867 - 07/14/12 06:14 PM Attachment (36 downloads)

Started with 100 grit in a rubber sanding block.

The final seam after I rolled it up had the most squeezout and needed the most sanding, but even that went fairly quickly:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5317871 - 07/14/12 06:16 PM Attachment (29 downloads)

near the ends of the tube slats, my thickness planer tended to make shallow grooves in the slat, but they sanded out pretty quickly, too.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5317874 - 07/14/12 06:18 PM Attachment (37 downloads)

and that is a knot on the left. I figure I'll cut a little off each end to make it nice and true on the ends, so this will probably be gone when I'm done.

All done with the 100 grit. Gonna switch to 220 in a tad.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5317877 - 07/14/12 06:18 PM Attachment (37 downloads)

I love this grain!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5317954 - 07/14/12 07:19 PM

Me too!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5318211 - 07/14/12 11:16 PM Attachment (36 downloads)

I decided I wanted to stain the tube and bring out the grain a bit more. I used a Brazilian Rosewood gel stain from Minwax. Oil based.

One coat. I might put another on tomorrow, depending on how I feel about it.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5318213 - 07/14/12 11:16 PM Attachment (40 downloads)

Closeup, where the grain gets pretty wild!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5318268 - 07/15/12 12:05 AM

Great wood deserves your best efforts.

That's one big beautiful glue-up!


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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5319004 - 07/15/12 03:07 PM

I love it! Wonder if I could do a tube like that for a 12.5f 4.8. Might be a bit heavy. What's that tube weigh Tim? I love Circus canon Dobs, much easier to set up. Tubes have advantages. Beautiful work!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: Paul Drufva]
      #5319042 - 07/15/12 03:50 PM

Hi Paul.

I should weigh it! I don't know what it weighs, but it's lighter than a fiberglass tube. I still have to finish it and make tube rings for it, attach a focuser and make the primary and secondary holders. This tube a out
1/4" thick. For a 12.5" I think I'd go with 3/8" if made out of wood. Depending on the wood, it could still be fairly light.

I think I'll be lucky to get the finish close to done today. Then it could be quite a while before I can work on it again, since we'll be landing Curiosity on Mars on August 5th.

Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5319283 - 07/15/12 07:34 PM Attachment (33 downloads)

I put a 2nd coat of stain on and wiped off the excess. I like the tone.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5319285 - 07/15/12 07:35 PM Attachment (37 downloads)

I'm figurin' that the focuser needs to go here!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5319293 - 07/15/12 07:40 PM

I had been planning on spraying a clear lacquer over it, but I can't get any that's not in a rattle can, and lacquer will dry so fast I won't be able to spray with out getting a very blotchy result.

So I bought a quart of oil-based spar polyurethane. The stain was oil based, so hopefully they'll live happily together. I'd like to spray it, but the can doesn't say anything about doing that. So I guess I'll try brushing a coat on, and see if it flows out well enough to hide brush strokes.

-Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5319436 - 07/15/12 09:29 PM

The wood is looking beautiful! Maybe try out the stain+poly on a piece of scrap first?

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Re: Delmarvascopics 8" f/9 OTA build new [Re: allardster]
      #5319445 - 07/15/12 09:36 PM

That tube's really looking great, Tim!!
If you thin the poly down a LOT (50%) with mineral spirits, you can wipe it on with a rag... wipe a heavy coat on- then scrub as much off as you can with that same rag.... let it sit for 24 hours, then lightly scuff it with 0000 steel wool... repeat... twice or 3 times, and you'll have a beautiful finish on the tube!


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5320138 - 07/16/12 11:24 AM

Love that grain, beautiful wood!

It makes me want to try this myself. My initial thought was to use bead & cove joints. You've obviously done this before (I never have) so I wanted to ask you about the advantages of using the "tape roll-up" method.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #5320169 - 07/16/12 11:42 AM

Hi Wes:

I may do that, but the first coat I brushed on to see how well it flows and how long it takes to dry. I used Varathane Spar Poly, which dries more slowly than other oil-based polys I've used before. My favorite brand was Zar, which was used to refinish the floors in our previous house about 20 years ago. There used to be a couple places in So Cal that carried it around then, but I haven't seen it in a long time. That stuff flowed very well, such that there were no brush strokes when it dried in about an hour. Next time I tried a Behr oil-based poly, and the brush strokes were very prominent, even in a semi-gloss finish. I had bought a whole gallon, and I hated the results so much I think I gave it all away. But it dried fast, too.

I may try the rag application, but before I do, I'll give spraying a go, since I have a couple of decent HVLP guns and a new air compressor that can crank out the CFMs. I've thought about getting a BBQ rotisserie to rotate the tube while I'm spraying and while the poly is flashing off, to help avoid runs and give me a uniform coat.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #5320175 - 07/16/12 11:45 AM

Jeff:

Thanks! I bought a bead and cove bit set from Rockler a year or so ago, but I haven't tried it yet. I think the advantage to beveling the edges is that when you tape it up while it's flat, then when you roll it up the joints tend to get tighter. I'm not sure that would work with a cove and bit joint, but it might be something to experiment with. And if the joints are good and straight, the glue seams should be nice and fine.

I cut the bevels this time on the table saw. I should probably have used the jointer, as the glue seams are visible in a couple of places - or they were before I applied the stain, since the glue was darker than the wood. Now, they're not so apparent.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5320367 - 07/16/12 01:28 PM

The BBQ rotisserie idea is winner!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5391437 - 08/28/12 12:59 PM

Tim,

Know you've been busy. but "Curiosity" is getting the best of me.

Any updates on this project?

Mike


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Re: Delmarvascopics 8" f/9 OTA build new [Re: MikeMcCaskey]
      #5392075 - 08/28/12 07:06 PM

Hi Mike:

Was hoping to have some time over one of the weekends to work on it, but that hasn't panned out yet.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549125 - 12/01/12 05:28 PM Attachment (31 downloads)

I dont' know about you, but I hate the runs!

...in the finish, that is! That, and brush strokes. So for the next two coats of poly, after I'd sanded the brush strokes and runs out of the finish, I did what my luthier friend down the street suggested...

I thinned the poly about 40% with mineral spirits and applied a couple coats with a rag.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549136 - 12/01/12 05:36 PM

Think I'll rub another coat or two on after it dries (dries faster, thinned).

Next I need to decide on a focuser and secondary support. If I go with a sled focuser, I can make the profile really low and use a small secondary. I hope I have a 1" somewhere, but I don't think so. I have plenty of prisms from old binos, but I doubt they're up to snuff for a planet-slayer.

I even have a 3/4" mirror, but I doubt that's big enough. One thing, though. This is a planetary scope, and my imagers have 1/2" and smaller ccds in them, so the fully illuminated field doesn't need to be big at all. At least unless I want to actually look through the thing!

So, will see what I gots. If I don't have a small one, I might as well use a standard focuser. I could cannibalize the Lumicon helical from my 3" f/6 (along with the 3/4" secondary, perhaps), or buy one. I have a couple of 1 1 1/4" R%Ps laying around, plus an Chinese/Orion 2" R&P, but they're not fancy enough.

If I could figure out how to take them apart, I've got two really nice dual speed R&Ps from a pair of old, incomplete B&L microscopes, probably about 100 years old. Brass knobs, too. Would look spiffy on that tube. But the challenge is going to be getting them off the microscope columns and making them work as a telescope focuser. Will cogitate.

I'll post pix of one of these in a bit, in case someone has an idea that I'm not seeing.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549176 - 12/01/12 06:11 PM

I like the sled focuser idea. But that is much easier to execute with a stalk mount and I'm not sure how well that would work on a GEM. For a dob, one could make the stalk thick in the longitudinal direction and it should be pretty stiff.

I'll be interested to see what you come up with. The tube looks really great!

JimC


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #5549187 - 12/01/12 06:20 PM Attachment (29 downloads)

Hi Jim:

I'm going to cogitate on the sled focuser some more, but here are the other options I was thinking about, if I can figure out how to use them:

B&L microscope focuser:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549192 - 12/01/12 06:24 PM Attachment (19 downloads)

The B&L is problematic, since the mount for it, the curved stalk of the microscope, is all one piece. I'd have to cut it off the whole arm, and though there are a lot of parts missing from both 'scopes, I just can't bring myself to do that.

Spencer focuser. This one has a joint near the end of the arm, but I'll have to take things apart to get it off. If it's screwed on, the screws must be underneath the mechanism:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549198 - 12/01/12 06:28 PM Attachment (23 downloads)

Both focusers have two racks, or a rack and a worm drive. The big knobs are coarse focusing, and the small ones are for fine - and they must be something like a kagillion:1 ratio, because you really can't even see the motion, you have to feel for it. The B&L mechanism is somewhat smoother than the Spencer.

The B&L also has a rack under the stage for a light or something, and it's really interesting because it's got a ring there with a set screw that compresses a ring around the light, or whatever was in there. The ring ID is 1.5", so I'd have to sleeve it for 1 1/4" eyepieces, and the bearing area is small since it's not a tube. Worst is that the rack, although smooth, really is coarse:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549203 - 12/01/12 06:32 PM

So, I dunno.

I suppose I could use the Orion/chinese 2 inch focuser for now and replace it with a good quality 2-speed something-or-other. Or abscond the 1 1/4" helical from the 3".

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549205 - 12/01/12 06:33 PM

For a sled, I've thought about making a track out of aluminum channel and birch ply for the body of the sled and support for the eyepiece and spider assembly. Probably a V 2-vane, I'm figuring. Or a curved one.

guess I'd better look at my secondary collection next.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549211 - 12/01/12 06:39 PM

Oh, and for the adjustment, threaded rod and a nut for longitudinal feed, like on a lathe.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549265 - 12/01/12 07:08 PM

Now I'm really salivating to see a sled focuser, preferably with a lot of brass. It would be so awesome with your tube.

JimC


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #5549303 - 12/01/12 07:33 PM

I'd have to buy more brass! I have some, but probably not the best for this.

Just put another coat of the 'thane on the tube.

I have 2 Edmund 1 1/4" secondaries, but one is glued onto a single stalk. That's almost 16% obstruction!! Horrors!

I also have another JMI focuser, but its a 'fractor model, so long drawtube.

Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #5549318 - 12/01/12 07:43 PM

I made my sled focuser to work with a threaded rod and 1/2 of a nut (just like a lathe). The nut is mounted on a leaf of spring steel and the nut is pressed against the threaded rod. Doing this accomplishes 2 things. There's no slop between the nut and threaded rod, and I can push the half nut away from the threaded rod if I want to move the sled a large distance. The other advantage is that with the half nut I can use a fine threaded rod so I have very precise feel to the focuser.

The only key to a sled focuser is that the axis of the slide needs to be aligned fairly well with the optical axis (especially for short FL scopes).

John


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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5549371 - 12/01/12 08:37 PM

Hi John:

That's a great idea, and simple.

Do you have pics of your focuser somewhere? I haven't searched for sled focuser designs in a long time, so I could do that, I suppose.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549384 - 12/01/12 08:50 PM

My sig line has a link to an article I wrote long ago about the whole scope. (6" reflector). The pics of that area are small & fuzzy. I'll take a better pic of the focuser arrangement tomorrow morning in the light so you can see the shaft and half nut detail.

j2


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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5549419 - 12/01/12 09:19 PM

Cool scope!!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5550014 - 12/02/12 09:36 AM Attachment (58 downloads)

Here's 3 pics of the focuser. Please excuse the dust on the top surface of the Paracorr. I didn't realize it was that bad. In use (because this is an F4 mirror) the Paracorr stays in it's correct position relative to the main mirror. So this screw focuser doesn't get used anymore, but it keeps the sled in the right position (I built this configuration before I got a Paracorr). There is another helical eyepiece focuser that mounts onto the Paracorr so I can accommodate the different positions of field stops in different eyepieces.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5550021 - 12/02/12 09:39 AM Attachment (45 downloads)

Here's a view of the leaf spring and the attachment. In the above photo you can see the curved spider dimly on the right

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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5550029 - 12/02/12 09:43 AM Attachment (45 downloads)

Here is the half nut being disengaged by deflecting the leaf spring. The half nut is made from an aluminum block that is fairly long, tapped to match the threaded rod (3/8 - 24 UNF) and then sliced in half. Some deburring required.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5550197 - 12/02/12 11:42 AM

Thanks for the pics! They give me some ideas. I like the half-nut solution to going from fine to coarse focus. How much focus travel do you have? I'm trying to decide whether I want to accomodate things like my SBIG ST2000 with CFW10 filter wheel for the occasional DSO imaging - yeah, at f/9 the stars ought to be nice and sharp to the edge of the chip!... but mainly, this is a planetary imaging scope!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5550217 - 12/02/12 11:55 AM

Hey Tim,

too bad you can't use the microscope stand, that would be so steampunk'ish. very cool anyway.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5550218 - 12/02/12 11:55 AM

There's about 5" of travel in my arrangement. Excessive, but this is a very old detail from back in the day when eyepiece weren't so standardized. But for photography it will give you all kinds of flexibility; you should be able to accommodate almost any configuration. Making the sled longer than you need won't really affect performance as long as you keep the sled axis parallel to the optical axis.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5550288 - 12/02/12 12:45 PM

yes, and a long sled will be easier to align with the tube

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Re: Delmarvascopics 8" f/9 OTA build new [Re: John Jarosz]
      #5550325 - 12/02/12 01:14 PM

John -

Very nice sled focuser arrangement. Clever, well executed, clean. Thanks for sharing.

Dick Parker


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Dick Parker]
      #5561304 - 12/08/12 06:26 PM

So I couldn't stand the look of the rubbed on polyurethane. Sanded it with 320 sandpaper, then rubbed on some more gel stain to even out some bright spots a bit better than I had before. It's nice and smooth now, but I'll need to put something over the stain to protect it from wearing off. Prolly spray a thin coat of poly over it tomorrow or next weekend.

So now, I have to figure out how I'm going to mount the primary and the focuser. Going back to the beginning of this thread, you might notice that the cherry I made the tube from was only 5 1/2 feet long, so the tube is 6 inches shorter than the focal length (exactly 72 inches). I figured I'd make a removable cell for the primary that hangs off the end of the tube, similar to what I did for my 10" f/6, only longer.

Then, for the focuser, if I really do go with a sled, I'm cogitating on making something that could double as a "retractable" section/dewshield/lightshield/focuser that will fit over the outside of the tube and extend beyond the end during use. I've got a pair of full-extension drawer slides that I'd bought a few years back for a similar concept (a moving secondary support to put a camera at the focus of a 12.5" f/3.5 mirror, that i haven't finished). I'd mount the slides to the tube, and mount the extension/focuser to the slides. Then, I'd focus with the threaded rod and half nut, like John's focuser does, only the half nut would be mounted to the tube and the threaded rod to the focuser/tube extension, so it could retract with the extension for stowing the scope.

Since the extension would be a full-circumference gizmo, I could conceivably use a conventional spider and make slots in the tube to allow the spider to retract with the extension. But I think I'll make a curved one instead.

To avoid "ugly", I think I'll start with figuring out how to mount my lazy suzan rotating rings to the tube, so that I can use the same design elements/outer dimensions for both the focuser extension and primary support.

if I were a sketchup sort of person, I'd draft it all up before cutting any wood. But I'm not, really. I tend to make chicken scratch drawings with measurements to keep track of what's in my haid and identify what won't work, then start cutting and fitting as I go.

Whadaya think?

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5561355 - 12/08/12 07:09 PM Attachment (50 downloads)

So here's what I've gots:

The lazy susan rotating rings are very close to the OD of the tube. I'll need to make rings that the inner half of the lazy suzan ring bolts to that bolts (not adjustable) or clamps (better, adjustable) onto the tube. Initially, I was thinking of something along the lines of the forms that I used to clamp the tube during glueup, but I think I'll want something thinner and stronger than that. Thin, in the radial dimension, it can be wide, though. Maybe still set it up so it clamps around the tube, though.

And I remembered something: At one of the Rockler sales about a year ago, I bought a kit to steam bend wood. Will have to make a box for the steaming, depending on the dimensions of the stuff I want to bend, but I could cut thin strips of Maple and bend them around the tube, laminating them up as I go to make a multi-ply ring with the grain concentric rather than cutting something out of plywood and trying to pretty it up later.

Here's the tube with one of the lazy suzan bearings around it. The bearing is aluminum, but I was planning on painting it to look like brass.

Edited by tim53 (12/08/12 07:10 PM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5561359 - 12/08/12 07:11 PM Attachment (41 downloads)

Another shot showing the tube, the rings, and one of the forms used for glueing up the tube.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5561362 - 12/08/12 07:13 PM Attachment (42 downloads)

Tube, full length

Edited by tim53 (12/08/12 07:19 PM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5561376 - 12/08/12 07:23 PM

So, if I make steam bent maple multiply rings that have the same OD as the outer lazy susan ring, and put them on the outside of the rotating ring assembly, I could mount my steambent rings to the inner ls rings, and rig up a braking system that bears against the outer ring to keep the tube from rotating too freely. That way, I could leave the ball bearings in the rings and save a long, involved step of converting the rings into Cave-like rings like I did on my 10" f/6.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5561383 - 12/08/12 07:25 PM Attachment (42 downloads)

And so, if the steam bending Idea works like it should, I'll make 5 of these rings. Two will go on the outside of the rotating ring assembly, two on either end of the focuser/extension tube, and 3 at the primary end (one to reinforce the tube and two to make the primary cell.

And the primary cell and focuser/extension will be walled with the thin mahogany plywood I bent back when I was experimenting making the tube.

Edited by tim53 (12/08/12 07:26 PM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5561385 - 12/08/12 07:27 PM

Okay, its starting to get dark. Better figure on putting stuff away for the night.

Also, gonna dig up my steam bending kit and try to find those drawer slides and make sure they're tight enough to do what I want them to.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5565834 - 12/11/12 12:14 PM

This past weekend I mostly ran around looking for supplies and ideas, but I did manage to rub on another thin coat of poly (thinned about 60% with mineral spirits). It came out really nice.

I know some will cringe at this, but I've decided to make this puppy focus by moving the primary by mounting a custom cell support on a pair or bearing drawer slides. They don't seem to have any play over a good 6" of travel (more than I'll ever need), and I have 9" of length to use to mount the mirror support to them and them to the cell support, which will bolt to the end of the tube.

If I don't like it, I can replace it with a fixed cell and cut the opening for the eyepieces larger to mount a sled focuser.

Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5565844 - 12/11/12 12:21 PM

For the moving mirror focuser, I plan to move it with a threaded rod and nut between the drawer slides.

Since I'll have rotating rings close to the od of the tube, I'll have to run the focusing rod up the inside of the tube. At first, I'll probably put the knob on the sky end of the tube so if I need to change things, I haven't made any extra holes in the tube. But if it works well, I might mount the focus k on on the tube primaryward of the eyepiece and use a pair of bevel gears to turn the focus rod.

Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5567255 - 12/12/12 10:02 AM

Tim- It looked like you pretty well had your focuser design finalized... what made you change your mind and decide to go with the moving primary??? Do you think moving the primary may affect collimation much??
Glad the thinned poly is working good for you... I find it to be an excellent finishing method.
Wes


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Wes James]
      #5567542 - 12/12/12 12:57 PM

Hi Wes:

One of the main reasons for wanting to try moving the primary is that I won't have to make any unnecessary holes in the tube, other than a place to put an eyepiece. If I decide to abandon the moving primary, I can then design a sled focuser and cut the tube to fit it.

I don't expect collimation will change much with motion of the mirror. These linear bearings are nice, smooth, and tight, especially in the range of a few inches. Since they're 9 inches long, I'll also have good control on mounting them parallel to the tube's axis (my corners will serve as straight edges). I may make the mirror cell support that attaches to the slides out of square steel tubing (1/2"), welded together. So I don't expect there to be any flexure there, either. I don't think I'll need springs to take up backlash in the threaded focusing rod either - just let the weight of the mirror take up the backlash.

I would probably not try this with a big mirror, though.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5568011 - 12/12/12 05:47 PM

Very impressive workmanship Tim, that tube's a beaut! Looking forward to seeing the finished scope and how the moving primary turns out.

Quote:


The B&L also has a rack under the stage for a light or something, and it's really interesting because it's got a ring there with a set screw that compresses a ring around the light, or whatever was in there.




Re the microscope, my guess would be that a 'condenser lens' fitted in the ring which acts to concentrate light from the illumination source onto or through whatever is being looked at.

James


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5568415 - 12/12/12 10:52 PM

Tim -

I have my primaries in a cell that is contained in the OTA on three threaded rods. With this arrangement, I can move the primary. I don't focus it by moving the primary, but I can position the primary so that I can control where within the focuser drawtube travel the focal plane is.

Tme main purpose of the rods is that two of them extend forward and I have knobs on them so I can collimate the primary while looking through the eyepiece at a defocused star.

So, if you have difficulty making a robust moving primary focusing system, There is another alternative that will at least give you control of the location of the focal plane thus allow you to get your focal plane close to the tube and not necessitate making big holes and cut outs at the front end of your beautiful tube.

Dick Parker


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Dick Parker]
      #5568997 - 12/13/12 10:48 AM

Yep, that's the kind of thing I'm thinking.

I'm betting that it'll be easy to collimate and keep there with such a long focal length. I don't even expect there will be much, if any, image shift focusing this way. But in the end, even if I decide I don't like the moving mirror, I can just rebuild the cell and make a sled focuser at that point.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: amicus sidera]
      #5570155 - 12/13/12 11:38 PM

Hi,
I'm a latecomer to reading this post. But just in case no-one has suggested it. I would like to suggest that you consider using laminate flooring to construct a multi sided tube. The laminate comes in different thincknesses. Given it's strength and rigidity, I would use the thinest possible. The laminates click together along their long edge as well as at their ends. So you can make wider panels very easily and the joint can be glued or eopxied to achieve a really good seam. You can even click together sections to make them longer, glued of course. These laminates are already pretty much impervious to water so it would not be difficult to improve on that with paint or varnish, whatever. Once you have glued up sufficient sections for width and lenght, you can mitre cut them in preparation for glueing into a tube. A square tube need only be cut to length, and at 90 deg at that.
The only drawback to this material is that it is heavier than plywood, but I believe it is also a lot more dimensionally stable.
Open stock of laminate flooring is often available at you local harware store of choice. You only need to buy as many sections as you require for making the sections. For a 6" primary (f8 or slightly less) four pieces would likely suffice to make a square tube. Note that this stuff is hard on blades, so use a carbide table saw or buy extra blades.
Hope this suggestion gives some of you ideas to take my suggestion to the next level.
BTW, very nice workmanship on the tube.
Norm


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Norm Folkers]
      #5586082 - 12/23/12 06:18 PM

Hi Norm.

I thought about making a tube out of laminate flooring, but I think I like the uniqueness of wood better. A solid wood tube, made with thin stock and modern glues and polyurethane is amazingly light and strong. I'm pretty sure that this tube is lighter than fiberglass, and stiffer.

Today I put another coat of poly on the tube by rubbing it on. I definitely think that thin ing the poly and wiping it on with a cloth is the way to go from now on. So much neater than brushing and spraying!

Okay, I've *BLEEP*-footed around quite enough! Time to design my rotating ring mounts, end rings, diagonal support, cell, and focus mechanism (sled or moving mirror)!

Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5586083 - 12/23/12 06:19 PM

Auto editors crack me up sometimes!

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5586100 - 12/23/12 06:29 PM Attachment (44 downloads)

Took a pic:

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5588624 - 12/25/12 03:36 PM

So yesterday I made one prototype tube ring out of 8 layers of drywall shims wrapped around the tube and glued together. This to see how thick I need to cut strips of birch or maple to make the real thing.

Next, I made a steam box to use with my rockler steam generator. All I need now is to cut strips to try bending. One other thing I might try if I don't like the steam bending results might be a bending iron like guitar builders use. My son doesn't have one of these... ...yet!

Tim

Edited by tim53 (12/25/12 03:37 PM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5589475 - 12/26/12 10:54 AM Attachment (27 downloads)

I know that doesn't sound like much, so here's a pic of the prototype ring as I was laying it up by gluing successive layers of drywall shims into a ring on the tube. If the real thing comes out exactly this size, I'll need to provide a means of clamping or screwing it onto the tube so it won't slip off. Particularly the rings I use to hold the rotating ring assembly to the tube.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5589484 - 12/26/12 10:56 AM Attachment (25 downloads)

Here's what I was after - the ID of the ring has to be able to accomodate the OD of the tube, of course. But the OD of the ring I want to be comparable to the OD of the inner half of the lazy suzan bearings I'm using for rotating rings:

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5589493 - 12/26/12 11:06 AM Attachment (21 downloads)

And the idea will be to drill through those 3 holes in the lazy susan inner ring to mount it to the tube ring, and drill through the 6 holes in the outer ring (with plastic "feet" pressed in them now) to mount the spreader rods between the rotating rings, and the saddle plate for the tube.

With 8 layers of drywall shims and glue between them, the prototype is surprisingly stiff. So much so that I'm tempted to soak it in epoxy just to see if this might be a reasonable way to make custom tube end rings without needing a router or milling machine. It's not very attractive, of course, and drywall shims aren't inherently strong by nature (they need to be torn off quickly in shimming drywall, after all). But if epoxy would make it strong, it could always be painted or even veneered.

So, I bought this steam bending kit from Rockler several months ago for this exact project. ...and then it occurred to me that what I'm trying to accomplish might actually have been easier with a bending iron, like used by guitar builders to make guitar bodies. But I already paid for the steam bending kit...

Initially I thought that maybe I could forego making a steam box out of 1x stock and simply use something like 4" PVC and end caps to make the steam box. Only downside I could think of is that a section of pipe with end caps on it might resemble a "device" that could attract unwanted attention! In the end, though, 4" PVC would have been a lot more expensive than the 12' or so of 1x4 and 1x6 pine boards I already had on hand, even if I had to buy new to get them. And it looks like a box, not a bomb!


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5589512 - 12/26/12 11:15 AM Attachment (23 downloads)

From the other end. The blue capped thingy is the steam generator. Just fill with water and turn it on. I've even drilled a hole in the top of the box for a meat thermometer for monitoring the temperature inside the box. They say it takes about an hour in the box per 1" of stock to make the wood flexible enough for bending. I'm not sure yet whether I'm going to try to make one of these rings in one swell foop or with multiple layers laminated together (like the shims, but not so many). Guess I was planning on experimenting to see how flexible various thicknesses become after steaming. I may have to make an MDF jig to bend the strips around an clamp into place while they cool and dry, but I am hoping that they'll be flexible enough that I can just wrap them around the tube and use a band clamp to hold them.

A single-layer ring will of course need to be glued together at the ends somehow or a clamping mechanism devised like a conventional clamping ring.

Years ago, I made tube rings for a Meade 4" mirror lens spotting scope (looks like a 2045 SCT but it's not) out of embroidery hoops. They worked great. The ID of the inner hoop was almost exactly the OD of the spotting scope. What I did was to glue the inner ring to the outer, and then cut through the inner where the clamp gap is. Then I lined the inner ring with felt so it wouldn't scratch the tube. I used the original screw clamps for the embroidery hoop to serve as ring clamps. Worked perfectly.

Here's the steam box from the other end:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5589914 - 12/26/12 03:49 PM

Well, I can't work fast enough to prevent breaking 1/4" thick pieces. I think it's too cold outside, the parts get cold right after i pull them out of the box.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5590502 - 12/26/12 11:21 PM

Boiling works too. I've put wood in a water-filled steel pipe (yes, open at the top...) and built a fire under to boil it. Comes out like a big noodle.

Or is that TOOOO Cro-Magnon? Urgh!


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Re: Delmarvascopics 8" f/9 OTA build new [Re: ccaissie]
      #5590583 - 12/27/12 12:15 AM

I might try something like that at some point. I had to put everything away because I was getting too frustrated.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5591522 - 12/27/12 05:36 PM

Lots of vids on YouTube......I know that you have to move fast, prepare for a bit of spring-back and you can put the form and project into the oven to speed up the drying times.

I'll put my money on you getting the results you are looking for.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5591965 - 12/27/12 11:18 PM

Yeah, you're probably right. I did find some youtubes that suggested I should be able to get the steam box up to 200F. Mine wouldn't go any higher than 170.

I'll probably give it another go tomorrow, maybe throw a blanket over the box to help insulate it.

Took today "off" because it's our 37th anniversary!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5596325 - 12/30/12 03:08 PM

I wonder if I can post a pic from my phone?

Apparently not. There isn't even a resize option

Tim


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5596698 - 12/30/12 06:36 PM Attachment (23 downloads)

So, took a break to much some chips and email myself some pics.

I decided to make plywood rings after all. I still have a fair amount of scrap 3/4" chinese plywood laying around from the shelving unit I built in the attic, so I figured I'd use it. The lazy suzan bearings I'm using for rotating rings are 11 3/4" OD, and about 9 3/4" ID, whereas the tube is about 9 5/8" OD. So I need a pair of rings to go on either end of the rotating ring assembly to hold them tight to the tube and help stiffen them. I also decided this time to leave the ball bearings in the lazy suzans and add a braking system to adjust the friction so the tube doesn't rotate too freely. Decided the easiest way to do that would be to make the ring on the sky end have a knob or two to tighten against the outer lazy suzan ring (the inner one is fixed to the tube via the plywood ring). I'll probably make my own screw and knob using delrin rod for the screw so it can serve as the clutch surface.

Anyway, so one ring needed to be 11 3/4" OD to allow for the friction knobs to be added. The rest are going to be 11 1/4" OD so they don't stick out so far from the tube and look "funny", but mainly because that's how wide the numerous scraps are left over from making the shelves! I probably have enough of the remaining sheet of plywood to make them all 11 3/4" OD, but I need to use up scraps anyway.

I need 5 rings in all:

The two on either side of the rotating ring assembly, one on each end of the tube, and one on each end of the mirror cell section - that I need because the tube is only 66 inches long and this is an f/9.

I usually just plan these things in my head as I go, but sometimes I scribble up a sketch. I couldn't find any paper, so I used a piece of the plywood for this sketch:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5596704 - 12/30/12 06:39 PM Attachment (17 downloads)

Kind of hard for mere mortals to read and understand, huh? I decided to go with the sled focuser after all, since moving the primary would require the control rod to pass down the inside of the tube, since the rotating rings are on the outside and close to the tube.

Instead of using a router to cut the rings, I decided to turn them on my Harbor Freight 12" wood lathe. I think they actually call it a 12 3/4" lathe, but I doubt you could swing something that big over the bed. The head swivels to turn bigger bowls, but I won't need that much room, so I'm not swiveling!

Here, I'm attaching a roughed out blank to the faceplate of the lathe.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5596705 - 12/30/12 06:40 PM Attachment (22 downloads)

And here it is mounted in the lathe:

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5596714 - 12/30/12 06:45 PM Attachment (42 downloads)

First I turned the OD and sanded it smooth. Then I buttered it with some water-based polyurethane, and used a heat gun to dry it quickly (about 15 minutes instead of 2 hours). Then I sanded it smooth again. Finally, I parted it off the blank by gouging out the inside until the ring came loose. After that, I took the separated ring and sanded the inside on a spindle sander. I've checked the fit of these first 2 rings on the tube (actually, there's a third, but I used some old oil-based poly for it, and it's still tacky, so I don't know if I'll use that one).

Then, I grabbed a bag of chips and jar of dip and came up here to post the pics, since I can't figure out how to load them directly from my phone. I'm going to try to get the remaining rings cut out today so I can poly them all over and let them dry good and hard before working on them again tomorrow. If there's still daylight, I might start cutting the 1/2" aluminum bar stock into ring spreaders for the rotating ring cage.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6390818 - 02/22/14 04:27 PM

Ah! Herrointment helped me find this thread, since I was on my iphone and my search didn't work.

I had started a new thread, but now that I know where this one is, I'll continue here.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6390828 - 02/22/14 04:33 PM

I may do the rings over. I've been using that disk I mounted to the faceplate on my HF wood lathe as a faceplate. I could easily mark mounting holes around the thing that could double as spacer holes for the rings on the scope as well as help me make everything concentric and quick. I've got a bunch of fiberglass resin, cloth, and matting, plus some "bondoglass" for filling, so I think I can make some purdy rings fairly quickly if the ones I have thus far aren't sufficient.

I think I'll cannibalize the 3" f/6 Edmund I built a couple years back, where I used a Lumicon 1 1/4" helical focuser and a 3/4" secondary, and use them for this 8". Rather than make the mirror cell move fore and aft for focusing or troubling with a sled focuser.

-tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6449184 - 04/05/14 03:18 PM

I think I musta lost a few posts in The Great Upgrade/Downgrade. No worries, though. Progress is slow, what with all the other things I'm doing these days.

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6449203 - 04/05/14 03:30 PM Attachment (17 downloads)

I was going to make just two of these "saddle plates" to bolt the rotating rings to for stiffening, and to mount the scope to a mount, with rod/spacers along the sides. But I decided that if I just made 4 of the saddles, I could mount accessories on the side of the scope as well as on top, so I made 4. When I bolted them all together for a dry fit, it occurred to me that I might as well make the inner part one solid piece with the outer races of the rotating rings attached, and then the inner races and plywood rings for attaching to the tube could be taken off for cleaning, lubing the bearings, and painting the components. So I think I'll fiberglass all the wood parts together. I may keep working on the other components of the OTA (need to make a mirror cell, spider, and sled focuser) so I can put it all together and try it out, maybe before finish sanding and painting.

-Tim.

Edited by tim53 (04/05/14 03:31 PM)


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6449210 - 04/05/14 03:34 PM Attachment (19 downloads)

Detail of one of the rotating rings. The assembly is just sitting near the end of the tube, but I have made sure I can slide it up the tube. I'll probably screw it to the tube when I've built everything and know where the balance point is.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6450075 - 04/06/14 01:01 AM

Watching this makes me want to get a similar mirror and dust off the old woodworking tools.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: woodscavenger]
      #6450153 - 04/06/14 02:18 AM Attachment (15 downloads)

Go for it!!

Now, this is going to look pretty awful, but it's progress! I'm using "Bondoglass" to fill voids in the wood structure and I'm making the outer races of the lazy suzan bearings integral to the "cage". I did make sure I left openings so I can access the plug to allow removal of the ball bearings and get the inner races off for when I go to paint everything.

I'll apply resin over the bare wood to fill and seal it before I paint. I'd use epoxy resin, but it takes too long to cure and I'm impatient!

-Tim.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6451466 - 04/06/14 07:09 PM Attachment (16 downloads)

Getting slightly purdier. I took out the plugs and "drained" the bearings int
Plastic bags for cleaning and reassembly later. Here, I'm working on filling remaining voids after a sanding.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: woodscavenger]
      #6452613 - 04/07/14 11:59 AM

Quote:

Watching this makes me want to get a similar mirror and dust off the old woodworking tools.




Well, Carl Zambuto currently has advertised on his web site a 12.5" f/9.3 mirror available for immediate delivery.

The RTA numbers on it must be phenomenally low. I am very tempted …..


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #6475667 - 04/19/14 02:29 PM Attachment (9 downloads)

Back at it! Last weekend was a "house" weekend, but this is a "toys" weekend!

Here's the idea. I've put a first coat of black paint on the cage, and already decided that the osh black paint dries too slowly. It's dry after several hours, but it loads up sandpaper too easily still. I want to get this done soon so I'm switching to a primer for the next few coats to fill the grain, then I'll come back with the semi gloss black for the final.

Here, I've bondoed a couple spots and have the inner race/ring standing next to the cage. The ball bearings and plug are safely stored in plastic bags.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6475668 - 04/19/14 02:29 PM Attachment (9 downloads)

Too

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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #6475734 - 04/19/14 03:01 PM

Quote:

The RTA numbers on it must be phenomenally low. I am very tempted …..





I guess the eye piece height would be an inversion of the RTA.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #6475947 - 04/19/14 05:24 PM Attachment (5 downloads)

That looks nice, Tim. I am considering my options for a project of my own and was wondering what brand of lazy susan bearing you are using. It looks well-designed since there is a integral loading "port" to add or remove the balls. A couple of other comments: you can get a vinyl strip with a u-shaped cross section at auto-parts stores (intended to be put over door edges) that might help protect the fragile tube ends temporarily while you are working it all out.

Also I am wondering about the stresses on the particular saddle plate/bearing joint that will ultimately be supporting the telescope. I see that you refer to it as 'bolted' but I don't spot a fastener in the pics. You might consider a way to tie everything together around the circumference of your cradle assembly, which would avoid overloading one particular hexagonal face. (Not meaning to be critical, but I have been wrestling with similar issues) Like a strap, basically.

Here is a different approach to a wood & aluminum cradle for an 8" newtonian, my modified OC mount:


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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #6476103 - 04/19/14 07:02 PM

Quote:

Quote:

The RTA numbers on it must be phenomenally low. I am very tempted …..





I guess the eye piece height would be an inversion of the RTA.




I forget. What's an RTA?


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476109 - 04/19/14 07:07 PM

I bought the bearings from vxb.com but I think they all come from china.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476133 - 04/19/14 07:21 PM Attachment (6 downloads)

I keep finding goobers to fix. I'm going to have to call it good enough soon or go bonkers.

I remembered a "trick" I used to use to quickly fill grain on the bigger facets: mix a small batch of bondo "hot" with plenty of hardener. It hardens fast and hard, so I can keep working.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476137 - 04/19/14 07:22 PM Attachment (5 downloads)

Tooo

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476231 - 04/19/14 08:22 PM Attachment (6 downloads)

Inner race/rings. Gonna have to touch these up a bit. I used krypton gold, which has a bit of a copper cast to it. Osh'a own gold looked more like clean brass to
Me, but they don't have it anymore.


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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476235 - 04/19/14 08:23 PM Attachment (7 downloads)

And the cage. Have to me tack so I can paint the other side.

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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476357 - 04/19/14 09:36 PM

Silly phone! What did I just say? Lol

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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #6476609 - 04/20/14 12:31 AM

Quote:

Quote:

The RTA numbers on it must be phenomenally low. I am very tempted …..





I guess the eye piece height would be an inversion of the RTA.




Depending upon how you built it, somewhere just over 9 feet.

Checking the Zambuto website I see someone snapped it up fairly quickly.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476620 - 04/20/14 12:42 AM

Quote:

Inner race/rings. Gonna have to touch these up a bit. I used krypton gold, which has a bit of a copper cast to it. Osh'a own gold looked more like clean brass to
Me, but they don't have it anymore.




Krypton? KRYLON, you fool phone!


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Jeff Morgan
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6476674 - 04/20/14 01:42 AM

Quote:

I forget. What's an RTA?




Relative Transverse Error. Also known as the Millies-Lacroix Tolerance. Zambuto talks about it here. If you have the Sky & Tel Archives, there is a nice article on it in the February 1976 issue. Basically, RTA is a proxy for the small scale slopes (smoothness) of the mirror surface.

Relating to this thread, the long and short of it (so to speak) is longer focal ratios tend to have lower RTA numbers with a lot less work. Which is something that anyone who has been around the barrel a few times knows intuitively.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #6477600 - 04/20/14 03:56 PM Attachment (13 downloads)

So the cage is getting close to complete. I've got to touch up where I left it resting in a piece of sonotube to dry last night, but I think the next step is to drill holes in the "plates" for installing thread inserts for mounting and accessory attachments.

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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6477616 - 04/20/14 04:09 PM

regarding RTA on CZ's yahoo usergroup Cal Marlett has some recorded txt from CZ.

in one of the documents CZ writes about how someone showed him that IF can be used to develop a mirror profile and more acurately measure the shell of the parabola. but all too often IF is only used up the the 3rd order, stig.

so he uses RTA from his ke as a way to develop a mirror profile as in his friends IF. thats why they test, test and more tests before a mirror is finished.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #6477742 - 04/20/14 05:41 PM

I must be working hard, because I've sanded my thumbprint off and have to key in my password to unlock my phone!

Tim


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6477986 - 04/20/14 08:15 PM Attachment (13 downloads)

So here's the idear:

I've got the cage/rings assembled and the tube is sitting in there. Once I build the rest (cell, sled focuser/secondary support) and know where it all balances, I'll affix the "brass" rings with the lazy Suzan inner races to the tube. I also still need to put thread inserts in the cage to mount it to the njp and attach the guidescope to it (and other accessories to the side plates and stuff.

But I like how it's going so far:


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6477990 - 04/20/14 08:15 PM Attachment (13 downloads)

And

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Mirzam
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6477998 - 04/20/14 08:19 PM

Looking real nice Tim!

JimC


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figurate
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #6478033 - 04/20/14 08:39 PM

Looks like a million bucks! The gold color is a perfect transition between the wood tube and black cage.

Fred


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: figurate]
      #6478068 - 04/20/14 08:58 PM

Thanks guys!

Jim, this is that same mirror I finished at the class 2(?) years ago.

Of the various paints I'm using, I like the krylon the best. The gold dries fast so I can sand in about a half hour. The osh black stays soft for days. I'm going to have to touch it up toward the end, one I have everything done and working right. The rust oleum isn't bad, but it takes a while to dry as well. I had bought a bunch of blue, but it's navy and a bit too bright for this project. So it looks like the model a ford engine green for the mirror box and guidescope.

Tim


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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: figurate]
      #6478108 - 04/20/14 09:29 PM

Quote:

Looks like a million bucks! The gold color is a perfect transition between the wood tube and black cage.

Fred






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Jeff Morgan
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #6478284 - 04/20/14 11:45 PM

Thanks for the link, it shall make good rainy day reading.

Here is another link to a compilation of CZ posts.


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Jeff Morgan
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #6478289 - 04/20/14 11:46 PM

Quote:

I must be working hard, because I've sanded my thumbprint off and have to key in my password to unlock my phone!

Tim






Hope you remembered the code.

I guess you can now say that you have "skin in the game".


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herrointment
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #6480080 - 04/21/14 09:59 PM

The tube looks very nice!

Gold and black lookin' good.....


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