The Practical Telescope #3
by Dennis Allen
I was cleaning out the attic to our club house when I came across an 8.25" wide, 8.25' long black fiberglass tube. This tube had a 6" mirror, mirror cell, secondary in a spider, and focuser. I couldn’t believe it. How did this telescope get into the attic? Must have sat there at least a decade. I decided to try and get it in working condition.
The old focuser was shot, so I ordered a basic 1¼" rack-and-pinion focuser from Orion telescopes. Now this new focuser required a slightly larger hole. Have you ever tried to drill out a 1¾" hole in an existing 1½" hole? Not pretty. After chewing up fiberglass, I took a piece a ¼" plywood and drilled a 1¾" pilot hole. Then I used the old focuser mount holes to screw down the plywood. Worked great. Next time, however, I have to remember to make a wood jig FIRST.
Now the tube diameter is 8.25”. Couldn’t find any tube rings that size, so I went old school and fabricated a simple tube box. Three ten inch square pieces of ¾" plywood, screwed together to fit around the tube. Two foot long 5/16" screw rods with wing nuts at the top of the box allow you to tighten the box around the tube. At the bottom of the box, couple of ¼" bolts with wing nuts to secure to the mount. To finish the box, I lined it with self-adhesive green felt, and put down a coat of Polyurethane.
Next, I made a simple pipe mount. We already had a 2" pipe base from another donated mount. This base consists of three sections of ¾" plywood., 21" long, 7 ¼" wide at the base. They come together to form a triangle, 6" to a side. There are pieces of wood that cover the bottom and top of this triangle, the top capped by the 2" pipe flange and a 2' length of 2" pipe. To this base I added 45-degree elbow (our latitude is 43-degree). From the elbow, another 2" short pipe to a tee. One end of the tee I attached another short pipe to a 2" floor flange. I mounted the flange to a simple wood plate for the tube box. The other side of the tee I used reducers to go from 2" to 3/8", to which I added a one foot section of 3/8" pipe. Used couple ¾" shaft collars to hang my 5lbs. cast-iron barbells. Oh, since I have a 3/8" shaft and counterweights with a 1" bore hole, I found that a short ¾" PVC riser makes a good bushing.
I used black lithium grease on the threads and just tighten the pipes with my fingers. Took it outside and the scope worked! Motion is smooth. There is no backslash and it stays where it’s pointed. The tube box makes it easy to adjust for balance and keep the focuser in a comfortable position. For a finishing touch, I added a small finder and Red-Dot Laser pointer.
Anyway, I hope this project gives you an idea how to build or refurbish your own telescope. Telescopes need to collect star light, not attic dust.
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