Posts Made By: P. Lee Stock

They look great, but here are my questions:

Would these be a pivot bolt replacement? If so, are they heavy enough not to shear apart when turning the scope?
How would you mount your azimuth encoder?

If it passes these criteria, then I could get really excited about it--I really hate dragging cables and don't really enjoy making brush systems that avoid the center bolt, but at least it works and lets you use a heavy duty pivot bolt drilled to receive an encoder shaft.

Who needs the Hubble any more when you've got a Toucam Pro and a 10" TMB?

And too bad there are no craters on Saturn, because we'd be looking at them in amazing detail with that setup.

Another solution is to replace springs with another material that compresses and expands but won't permit the cell plate to laterally shift or rock. I like to use rubber stoppers. I simply drill holes through the center of the stoppers for the collimation screws to pass through. They are usually 1" tall and come in various diameters. I find them at my local Lowe's Hardware.

You could make a full scale representation of your light cone using butcher paper and fold it to simulate your intended design. Measure at the fold(s) to determine the size of the mirror(s) that would be required.

Hi Evan,

It wasn't the SBIG, that was already on the floor. It was something else. Look around...

;^)

The mount is doweled together, but I used these antiqued "table leg" braces to clamp it as the finish is thick and a little soft still. I thought they looked nice--they match the dark wood theme.

Even though it has been over 2 weeks since I sprayed the last finish coat, wood clamps would leave marks behind unless I waited another couple weeks or so, thus the braces.

By the way, this is an 8" f/6. The mirror is one of the few loose Carl Zambutos floating around out there. The rocker sides are 1-3/8" thick--two laminated sheets of Baltic birch. With the bracing, the rocker sides hardly flex at all and should (will ;^) provide rock solid views.

1/2" thick would work just fine for a bearing surface--assuming you're making a dob of some kind. Only issue is that by the time you leave a small gap between rocker and bearing box, there's not much bearing surface left. I typically leave 1/4" gap, so that would leave only 1/4" riding on the Teflon. I'd probably laminate two pieces together to get it to 1" thick.

Hi Jerry,

Hubba hubba ;^). That's nice!

To arrest all flexure in this design, you'll need to do a few things (I learned it the very hard and very expensive way):

1) Widen the sides of the arch on the rocker uprights to 3.125" or greater.

2) Laminate two sheets of baltic birch together for the rocker uprights. The width for each upright, if you are going to cut out the center of the panel as you have (and for a ~30 lb. OTA), should be at least 1". I'd go with 1.25" myself. 1.5" would likely be overkill, but it won't add that much weight, will look nice and will put you well in the safe zone. The dark cherry one in the other thread has 1-3/8" rocker sides and it is plenty.

3) Triangulate the rocker just inside the upper eyepiece racks as shown in detail the other thread.

4) Optional (but to achieve ultimate stiffness): Cut and install a semi-circular aluminum brace from 1/4" thick aluminum, 1" wide and long enough to span across the back of the rocker bottom plate from rocker upright to rocker upright. Install it with countersunk screws just inside the Ebony Star ring of laminate and Teflon pads underneath the rocker plate (hidden from view). This will all arrest flexure in the bottom plate that results from those attractive and decorative half-moon cutouts. Or, just leave the bottom plate one solid 3/4" piece. I prefer to reinforce, though it is only necessary on a tall 8" f/7 and 10" scopes f/5 and longer.

5) Optional: You notice I used a really thick ground board because the load is cantilevered. You can cut some more reinforcing aluminum in the shape of your extension feet and screw it to the bottom of each one to add stiffness. I do/did this on all scopes larger than an 8" f/6 until I went with the the double thickness laminated ground board.

Aluminum cuts pretty easily with a bimetal blade in a jig saw--18 TPI to 24 TPI. Keep the speed on the blade down so you don't heat it up and clog the teeth. You can add some oil to help. To give it a nice finished look, sand it with 100 to 150 grit sandpaper using an orbital sander.

If you're going to rebuild the rocker from scratch, consider making the rocker sides/uprights the same width as viewed from the side as the tube bearing box.

Aaah, the challenges of balancing aesthetics and structure on a higher center of gravity tube scope... kept me up many a night and cost me many a dollar.

Good luck!

"Lee"

PS - This early scope of mine, below, had to be redone as described for the same reason. Any telescope I make now is so stiff you have a hard time seeing a visible response to any tapping or movement of the tube when viewing through an eyepiece at high power. Lesson learned.

Jerry,

Taking another look at your scope, I think I might remake only the sides, without the center arches. You might be able to get 1" sides on the bottom plate without extending over the edge. And even if you used 3/4", it would be much stiffer after triangulating near the inside top. It would also balance nice visually with your bearing box/"rocker".

Just something to consider--a quick and effective correction without having to redo everything.

Take care,

Lee

Hi Matt,

That is stunningly gorgeous and very technical-looking all in one package.

Please say more on the contruction and materials for the various components. Does it easily come apart into something transportable? What parts are wood, metal, or other? It is an Alt-Az design? How are the movements?

I'd love to see photos from more angles.

Thanks for sharing...

Lee