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 equatorial 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 (note the bottom triangle piece never actually touches the floor). 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. For a finishing touch, I added a small finder and Red-Dot Laser pointer.
Last Saturday was my first chance to try out the equatorial pipe mount. To tell you the truth, not happy. I was constantly flipping the scope and rotating the tube, depending on the area of sky. And my 45 degree elbow kept wandering away from Polaris. Very aggravating.
I thought about adding set screws and fabricating slow motion controls, when a visitor suggested I convert the scope to a Dobsonian. Well, a rocker box for this scope would be very tall. The center of gravity would be extremely high, almost unsafe. Then I saw images of cloudynights.com pipe piers. Most of them were just a tee, scope on one side and counterweight on the other side. I never considered that design, since I didn't think I could get the correct balance. Ah, but I already have the correct balance from the equatorial mount. So I removed the elbow and went to a straight tee.
Last open house of the season, I finally had a chance to try out this scope. Started out a little shaky, so I switched from the tripod to our permanent pier. More steady, marked improvement. I also added grease to the pipe joints. Again, real improvement. Movement is now real smooth and steady. I must say, I like this mount. The scope moves and stays put like a Dobsonian. No need to rotate the tube, the focuser is always where I need it.
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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