Sunday, December 10, 2023

Crowd Sourcing a Small Equatorial Mount

 Over at Cloudy Nights, I have been promoting the idea of a crowd-sourced homemade equatorial mount for smaller telescopes (under 15 pounds).  It would be rather like a Losmandy GM-1 instead of their GM-8.

The problem is that since Vixen's Japanese-made Super Polaris mounts were driven out of the American market by Chinese clones of the Vixen SP, the only choices are PRC or heavy and pricy like the Losmandy which I love but are a bit heavy for ocassional use with a telescope like my Televue-85.

I was thinking about the design problems after church and I suddenly realized that the obvious 1" steel shafts for the polar and declination axes needle bearings inside 1.25" ID aluminum housing tubes had a more elegant solution.

I was looking for sources of needle bearings, 1" OD steel rod, and 1.25" ID aluminum tube, and I wondered "Would aluminum rod be stiff enough?"  Then I thought a little longer.  Would .5" carbon fiber composite be stiff enough?  Yes and far lighter.  Instead of aluminum tubing, use carbon fiber composite tube.  Especially in these smaller diameters they are available and not hideously expensive.  

Fasteners are an issue.  Steel has a electrochemical corrosion problem with carbon fiber composite.  So does aluminum.  Stainless steel is apparently pretty good except in seawater.  (Stay out of the ocean.)  Titanium is apparently perfectly fine.  The needle bearings are steel but there are barrier materials to handle this.  See this discussion about the corrosion problem.  Many parts are best bonded with epoxy; only items that might require replacement should be held by screws. 


I suspect you could make a very stiff mount with 3' tripod weighing about five pounds with extraordinary stiffness.


This would likely require carbide taps; steel taps will likely be substantially dulled in carbon fiber.

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