Thursday, August 10, 2023

Perfection by Approximation

I took the 8" OTA off the mount today to see if the new mobility solution worked.  The thumbscrews that hold the inner legs in position within the outer legs did indeed turn out to be 3/8"-16.  (Losmandy uses this size a lot.)

However the inner legs do not close flush with the outer legs so the the 3/8"-16 holes would not clamp to the outer leg.  In addition, I made the spacer .1" thinner than needed and there was more slack on the sides than needed.


1. Make these with another inch of sleeve length.  

2. Add another thumbscrew to the side to clamp side to side, fixing the spacing problem. I think I will try to find thumbscrews with nylon tips to avoid marring the surface.  (Alas, where I attached the existing mobility solution to the inner legs looks terrible.  The surface is scratched and the inner leg is a bit dented.  I may be able squeeze out the dent from the inside and paint over the scratches.)

3. This time, instead of using a spacer, machine the acetal insert to fit the leg instead of fixing the problem with a spacer and the associated attachment holes.

I am not putting it all back together again until I have remade these.  At least this way I can try the first article on the first leg without going through the process of disassembling and reassembling.

UPDATE: My wife, who has a superior spatial sense than me, pointed out that shortening the existing legs that clamp onto the interior legs would allow a much shorter height and only require cutting the current set and tapping a few new 1/4"-20 holes in each assembly.  Far faster than starting from scratch and only a couple inches higher than the solution I have been pursuing.

Instead of using the 1/4"-20 hex head bolts that scratch the anodized surface of the inner leg, I think I will use plastic knurled thumbscrews instead.  The bolts are not carrying any load.  They only make sure these caster assemblies do not fall off the inner legs if we lose gravity (not likely).

I also ordered Parallax Instruments rotating tube assembly which allows the OTA to turn to whatever position is most convenient.  The German Equatorial Mount design has many virtues. One of the irritations is that the eyepiece can end up in positions so awkward that they can require severe contortions, sometimes on a ladder.

UPDATE 2:  I trimmed 2.5" off of each sleeve allowing me to lower the inner leg that much into the outer leg lowering the OTA what is that 2.5" cos 30?  That would be about 2.2".  That sounds right.  The footprint is smaller.  2.5" sin 30 would be 1.25" on each side?  Feel free to correct my imperfectly remembered trigonometry.  My wife also suggested, okay, maybe a stronger verb is appropriate, that I move the 5" f/9 refractor out of the back corner creating more room for the reflectors.  

There is now no shortage of room in the telescope shed for getting either reflector in and out.  The refractor is on the back patio under a cover.  This makes it a little more rapidly accessible for astronomy.  Perhaps I will find some way to get it into the garage for faster access out front.

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