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Equipment Discussions >> ATM, Optics and DIY Forum

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995454 - 07/28/13 08:51 PM

I've had a couple of weeks to put some more hours into this project. Originally I wanted this thing together Aug 1st, that is not going to be the case, Perhaps Sept 1st!

Once the box was put together I took a fair amount of time working on the altitude bearings. I thought maybe I should use some cast aluminum tube caps from a 60's fiberglass newt tube I had salvaged. The rings are 11" dia but I was having fitting and mounting issues. The rings were no more than 1/2" wide and tapered immediately to 1/4". The problem that I couldn't get my head around was how to drill through the sides of the box and hit the rings to an accuracy of 1/16" inch or so. After a week or so I went back to my original idea of a 24" wooden disk cut in half and glued directly to the sides.

Then I got tricky. I figured with a scope this big, at some point I'd like to have both axis driven. Also, if it's on an eq platform, I would need to be able to lock things down to change eyepieces(that is going to be a process!) or check out the charts. When thinking about movements and big things, the magic of materials gets kinda hard to figure out ahead of time. One thing I learned building my Eq mount is that you have to build things to move nice and easy, then you build a brake. Thinking about materials that will do both can be a roll of the dice and when things get big and heavy, everything moves nice and easy!


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995461 - 07/28/13 08:56 PM Attachment (34 downloads)

So I roughed out the sides and bottom of my base out of my chair sides and nice hunk of wood. I figured with my skinny wood bearing disks, I could have each side bearing just inside of each chair side. I sourced a handful of nice sealed captive bearings. I cut 4 pieces of 1/2" threaded rod and tapped straight into the oak sides...

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995501 - 07/28/13 09:15 PM Attachment (25 downloads)

The brake took a fair amount of figuring. I figured that if I mounted one bearing away from the side of the LTA, I could use a bar and clamping knob to provide a good braking action. I put the brake on the same side as the focuser to minimize any torquing action from moving the scope around by the UTA.

I used a hole saw to cut out some disks of UHMW Polyethylene and mounted three on the inside of the oak chair side as well as 3 in a piece of strong ply. I had to cut out some material and countersink the UHMW pads for clearance.


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995522 - 07/28/13 09:21 PM Attachment (24 downloads)

After a lot of roughing, measuring and mocking up, the dimensions and construction fell into place. Sometimes I hate my brilliant ideas as it can take an hour to find the right bearing or bolt to fit the design I come up. This time it went together pretty smooth and the clearances were all right where they should be. With some spacers and a carriage bolt with a clamping knob and there you go, a brake.

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995527 - 07/28/13 09:22 PM Attachment (22 downloads)

The outside view...

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995542 - 07/28/13 09:34 PM Attachment (23 downloads)

I used a spring with the clamping knob to allow the braking bar to adjust to the wood bearing. It would be nice to have a perfectly straight and smooth side bearing, but this being the real world, a spring will keep the brake assembly from binding on any high-spot on the side bearing.

Next up is a little bit of beautification. I glued up the UTA out of my plywood rings and some plywood planks...

I picked up some red oak iron-on veneer tape and spent a night taping over all of the exposed ply on the UTA. It's a nice light assembly and kinda purty too...


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995546 - 07/28/13 09:35 PM Attachment (26 downloads)

Here is where I'm at now: a mocked up LTA. I will have to figure out a way to ensure the side bearings are parallel before gluing...

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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #5995786 - 07/28/13 11:44 PM

Quote:

Here is where I'm at now: a mocked up LTA. I will have to figure out a way to ensure the side bearings are parallel before gluing...




Thanks for the update Sean!

As for the parallelisms:

1) Not too critical for non-DSC scopes. In understand well it is a point of pride, but don't go crazy on it.

2) Parallelism starts from the Inside Out. If you have not already glued the mirror box, cut a series of spacers to maintain equal widths of the mirror box interior. Clamp it tight until the walls meet the spacers and do not use the edge cuts of the mirror box for guidance! Any excess edge(s) on the mirror box can be sanded down.

If the MB is already glued, you can use a spacer cut to the same width as the back edge of the mirror box and place it at the front edge of the alt bearings, shimming as needed any gaps in the mirror box.

Good luck!


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Jeff Morgan]
      #6033820 - 08/19/13 12:11 AM Attachment (25 downloads)

I made a bit of progress this weekend, I am at that great point where the end is far off, but in sight.

I have spent most of the last 2 weeks figuring out how I was going to attach the poles. So what did I do? something else.

First, the mundane. I glued up some oak floor board scraps and glued them to a sheet of 3/4 birch ply for a stiff base. Another problem had been working on was how to brake the azimuth axis. I was very please with my alt-brake and was looking for the same magic for the az-axis. The complication was I did not have the space on the bottom as I did on the sides. I needed a brake that was going to fit in 3/4 of space. I also wanted to use a lazy-susan bearing for easy movement. After digging through my parts pile I settled on a train-wheel style brake. I guess one of the benefits of building a bunch of scopes is that I have assorted circles and arcs left over from other builds and sure enough, this time my parts bin came through!

I started by finding a nice round and centered 12" disk of plywood left over from the interior of routing out disks for the UTA.

I spent some time truing the circle and sanding it smooth. I then centered it on the base board via center screw and after lots of careful measurement, attached the lazy susan bearing:


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6033837 - 08/19/13 12:24 AM Attachment (18 downloads)

The brake is installed on the LTA side so that I can have tensioning knobs for both axis on the same side of the LTA. I figured I could use some leverage, so I roughed out where the parts should lay. One thing to think about is that unless you have access to a lathe, a shoe-brake has to be able to travel, you can't just use a screw to push against the brake disk as any out-of-round imperfections will cause binding. What I want is not binding but a consistent resistance of movement. That means, much like my alt-brake, there has to be a spring involved which means I have to have a pulling action instead of a simple push type action. Now there is a penalty for getting to complicated in one's setup as well, but then what is life but a roll of the dice?


So here is what I came up with: a clamping shoe actuated by a simple lever:


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6033847 - 08/19/13 12:34 AM Attachment (23 downloads)

Here is everything finished up with a nice clamping knob, spring, etc. The wooden lever is actuated by a 1/4-20 eye-bolt which is tensioned by a spring and clamped by the knob. After reassembly, the clamping action is noticeable so we'll call that effective for now. If the clamp needs some help, we can always clamp down via the center bolt. We'll see how it goes though....

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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6034465 - 08/19/13 12:16 PM

Pretty clever - it looks like a drum brake with the mechanism on the outside instead of the inside.

I would think that humidity changes will raise the grain on the wood parts, changing the feel the of action. Are you going to attempt to seal that, or just retune with each observing session?


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Jeff Morgan]
      #6034562 - 08/19/13 01:09 PM

Thanks Jeff,

I've contemplated gluing a bit of sandpaper to facilitate everything wearing down. After a while, a bit of clearance will wear in and I can line each with a bit of plastic or aluminum strip. Or asbestos, whatever...


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MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6034606 - 08/19/13 01:41 PM

asbestos, lol Very nice work.

May I ask where your lazy susan bearing came from, its weight limit, and dimensions?


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: MessiToM]
      #6040029 - 08/22/13 12:22 PM

I bought that lazy susan at our local Menards(big box store). It is a little larger than 12" in diameter, about 1/4" thick and has a listed capacity of 250lbs, though I haven't seen one sweat yet. Usually they are too smooth with zero stiction, hence the need for the brake.

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6095753 - 09/22/13 08:58 PM

My deadline for first-light is the Illinois Dark Sky Star Party Oct 6th-ish. Hopefully a deadline will help! I have been working on all the little parts. What you gain in portability with truss construction, you pay for in complexity.

I began this project with lofty ambitions about how to handle the tube connections. I considered buying ball-connectors but I had second thoughts about having so much visible machinery, this being mostly wooden construction. I then talked to another ATM who had made wooden clamping blocks and was telling me about how expensive they were, since they had to be cut from one piece of wood. I must have gone back to the drawing board a dozen times!

I finally decided on a simple bolt at either end. For that I needed 6' tubes(technically 5'-6"L) So I went to my local box store and the only conduit lengths were 5' or 12'! Oh brother. Nothing like a mid-aisle redesign. So I could spend $8.60 and figure out something new or $120 on proper sized aluminum. Guess which direction I picked? Yep. $10.45 total with the bag of M&Ms.

That's okay, trying to figure out how to stretch 5' of tubing to 5'-6" of tube ended up fixing another issue, that of inevitable trimming of tubes. Having 8 tubes, I was not looking forward to that part. I have found ways with my other builds to have some adjustability for accessories like filter slides, binoviewers, etc.


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6095769 - 09/22/13 09:07 PM Attachment (11 downloads)

The answer came to me in the form of plywood tube anchors that would allow the tube to slide in and out. If I made them 6"l on the bottom and 3" long on top, I would give myself the extension I needed and it would fit in with the rest of the construction. The downside is all of the sawdust. My gosh, the sawdust from all the routing and sanding was not-to-be-believed!

Construction is simple, I routed a channel for 5" down a 7"l block. I then cut a back-plate that will clamp down on the tube end via screws.

Easy, huh. Now make 8 of them. Still have 10 fingers (whew!)


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6095787 - 09/22/13 09:15 PM Attachment (5 downloads)

For the other end, I followed the same methodology for construction with the channels and such however I opted to make each union whole rather than individual mountings. This is one area I often question both from a field-assembly point of view as well as a stability issue. For a stiff union, the forces from each tube should meet at the same point to form triangles throughout. Often with ball connectors you end up with a clunky assembly which makes trapezoids. They also take two people to assemble. I opted to make the tubing connectors one piece.

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6095793 - 09/22/13 09:19 PM

I routed the channels the same way and cut the slight 5deg angle to each side. I glued each side together with a channel in the center for further adjustment. A cam lever will provide quick assembly/adjustment, They are on order.

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: My 16" f7.2 Newt project code named "Grace" new [Re: Sean Cunneen]
      #6095798 - 09/22/13 09:22 PM Attachment (6 downloads)

The base of each tube mounts via corner blocks and machine screw anchors/clamping knobs. The top baffle/corner blocks will also unbolt from the LTA so I can completely disassemble the trusses or if I want to be up and going quick, I can unbolt the assembled trusses and UTA from the LTA.

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