Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> ATM, Optics and DIY Forum

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | (show all)
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
herrointment
Carpal Tunnel
*****

Reged: 03/12/11

Loc: North of Hwy. 64
Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5320367 - 07/16/12 01:28 PM

The BBQ rotisserie idea is winner!

Post Extras: Print Post   Remind Me!   Notify Moderator  
MikeMcCaskey
professor emeritus


Reged: 03/09/12

Loc: South Central Kansas
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549125 - 12/01/12 05:28 PM Attachment (26 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #5549187 - 12/01/12 06:20 PM Attachment (25 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:


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549192 - 12/01/12 06:24 PM Attachment (16 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:


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5549198 - 12/01/12 06:28 PM Attachment (20 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:


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
John Jarosz
Astro Gearhead
*****

Reged: 04/25/04

Loc: Fairfax, Iowa
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
John Jarosz
Astro Gearhead
*****

Reged: 04/25/04

Loc: Fairfax, Iowa
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tim53
Postmaster
*****

Reged: 12/17/04

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

Cool scope!!

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | (show all)


Extra information
13 registered and 23 anonymous users are browsing this forum.

Moderator:  ausastronomer, richard7, Starman81 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 7083

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics