Telescope Reviews: A push pull Crayford for beginners.

As a beginner, I really appreciated this. For my in-progress 8" F/3.93 travel-scope, I made a version using blocks of wood instead of the aluminum angle. The blocks are 3/4" thick hardwood, about 1 1/8" high and 1" long. They are at 120 degrees around the central hole. They are JB Welded into place, though I may eventually run a wood screw into each.

The drawtube is Schedule 40 1-1/4" conduit, which is about 1/8" too big in ID, but has a 1-1/4" plastic drainpipe top pressed inside it. (If I am not happy with it, I may take a new piece conduit--I still have 10 feet less 3 three inches left!--and line it with felt, which also gets me flocking, or maybe glue 1/16" teflon strips in it.)

The teflon is bondable 1/16" teflon ordered from Amazon's Industrial and Scientific store. It is glued to the wood with Shoe Goo. JB Weld would have worked fine, too.

The adjustable tension block was done as follows (after a false start). I cut out a segment of one of the blocks so the adjustment screw would have less wood to go through. I drilled a hole for a #10 thumbscrew, and tapped it by screwing the thumbscrew in. Turned out that it was too hard to turn, so I expanded just under half of the hole shaft into a 1/4" hole, and then screwed the thumbscrew in and out several times until it moved nicely. (I have some experience with the hardwood I used and think it will hold a thread nicely.)

I used Shoe Goo (a thin layer of JB Weld would work) to glue a square of metal (cut from a spare PC expansion slot rear cover) to the rear of the top half of a 1" x 3/4" teflon rectangle. Then I used JB Weld to glue the bottom half to the block. I may eventually run a screw through that bottom half.

Costs:

- 10 feet of 1-1/4" conduit: $2.77 at Lowes. Most of it is left for future projects.
- Thin plastic tailpiece for sink: $3.85. I only needed the top three inches. The rest was used to make a sight tube for a friend's scope.
- #10 thumbscrew: about $1 for a pair.
- bondable 1/16" teflon, 6" x 12" sheet: $8.69 (all prices include tax). Obviously, most of the teflon is available for other projects.

I also used scrap wood, scrap particle board and JB Weld that I bought for other purposes.

Total cost if I were buying everything for this: $16.10. About half of that is teflon which I needed anyway for other parts of the project. If one prorates costs based on amount of material used (assuming the rest of the material eventually finds a use), I used 7 cents of PVC conduit, $1.05 of tailpiece, $0.50 worth of thumbscrew, $0.36 of teflon and probably $0.25-0.50 worth of adhesives.

Edited by arpruss (09/06/09 09:48 PM)