Re: [ATM] Public Terrestrial Telescope and Don Clement's Comments About Turcite

["David Sleeter" <d.sleeter@roadrunner.com>]

Regarding Don Clement's comments about Turcite, Don is right. I got my wires
crossed. It's Nylatron that's made with molybdenum disulfide. But Turcite is
VERY "pricey". When I looked up Internet dealers that sell it, for 2"
diameter barstock I saw prices of $70 to $85 per foot with minimum 1-foot
orders.

Based on what Don says, it SOUNDS like Turcite would work, and aside from
its price and the fact that I'd have to buy more than I need, it looks
attractive. I'll definitely keep Turcite in mind for future projects.

Regarding this terrestrial telescope I'm designing, I'm now seriously
considering making the tube assembly work like a Celestron C8. That is, seal
the front of the tube with a fixed optical window. Then mount the objective
lens in a cylinder that slides forward and backward inside the tube. A small
leadscrew running in a nut at the back of the cylinder/lens cell would, like
the mirror mount on a C8, be connected to a small thumbsrew on the outside
rear end of the tube. The thumbsrew and its shaft would be the only external
moving parts, and aside from their small (i.e. 3/8" dia.) bushing and o'ring
seal, the entire tube assembly would be sealed from the weather.

I've been playing around with the idea for a couple of days now, and found
some ABS plastic pipe fittings at Home Depot and Lowe's that could be easily
modified/machined into the sliding cylinder/lens cell assembly for a total
cost about $9. And to top it off, I don't have to paint them because they're
already colored black. When I looked up ABS on the Internet, I found that
ABS pipe fittings have an expected life-span of 25 years, and that makes ABS
attractive. I think I like this sealed tube/moveable objective configuration
the best so far. The eyepiece and prism housings could then be rigidly
mounted on the rear end of the tube, like the eyepiece and diagonal on a C8,
and this would simplify the scope's construction.

Dave Sleeter


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