The Practical Telescope #2

The Practical Telescope #3
by Dennis Allen

This summer I spent some time restoring a couple of club telescopes. If not in mint condition, at least in working order. I was working on a homemade 6" German Equatorial telescope and needed a focuser. I found one in the attic of our storage building, attached to an old black telescope tube.

After getting that telescope working, I took another look at the black tube. I found that the 8" wide black fiberglass tube still had a 6" mirror, mirror cell, diagonal and diagonal holder. I couldn’t believe it. Why was this telescope in the attic? Was it ever used? Come to find out, somebody built this telescope but never made a mount. So it sat in the attic for over 12 years, having never been used.

Now this black fiberglass tube is over 5’ long. If I made a dobsonian mount, the rocker box would have to be over 3’ high. Then I remembered another member donated a homemade German Equatorial mount last year. So why couldn’t I put the two pieces together and make one whole telescope?

Before doing that I first had to replace the focuser I took. Novak doesn't have them anymore, so I ordered a basic 1¼" rack-and-pinion focuser from Orion. 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 create a pilot hole FIRST.

To attach a mounting plate to the tube, I went to Menards and got four 4" pipe clamps. Tying them in transit, I was able to wrap the tube and a 1"-by-4" strip of wood. On this piece of wood I attached the mounting plate for the ½" wide declination shaft.

Went to Wal-Mart and got five 5lbs. cast-iron barbells for counterweight. These weights had 1" bores, so I found a piece of ½" rubber hose for filler. To secure the weights I used ½" washers and ½" clamps from a local hardware store.

At first this unit seemed ideal. The Right Ascension shaft had a decent clutch, but the declination shaft was way too loose. Just a touch would send the telescope drooping. When I tried to tighten the declination wingnut, it broke. Now this homemade mount was made out of PVC pipe, sealed and self-contained. One would have to brake it to fix it.

I didn’t want to give up. A club member suggested I make a pipe mount. I didn’t understand. A German Equatorial mount made out of cast-iron piping? Would that work? I did an archive search on the Sky & Telescope magazine’s web site. Searched for pipe mount. September 1996, page 84 illustrates just such a mount.

Obtaining the parts was simple. Went to the plumbing section at Menards. I already had a 2" base, so I started with a 2" to 1½" reducer. From there I attached a 3" long pipe nipple to a 45-degree elbow. Our latitude is 43-degree, so it should work just fine for visual use. From the elbow, another short pipe nipple to a tee. One end of the tee I attached another short pipe nipple to a 1½" flange that mounts to the faceplate. The other side of the tee I used a 1½" to 3/8" plug, to which I added a 2’ section of 3/8" pipe. Remember that 3/8" pipe is 3/8" I.D., is which over ¾" O.D., so I needed 1" clamps.

Final Assembly

Putting the pieces together went quick. 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 real smooth. There is no backslash and it stays where it’s pointed. For a finishing touch, I added a Red-Dot Laser pointer.

Conclusion

About the only drawback so far is weight. The tube weighs about 25lbs. Add counterweights and piping and you got close to 65lbs. I did replace the pipe nipple between the tee and the elbow with a small all threaded unit. Was able to remove 10lbs. of counterweight.

If you’re interested is making a pipe mount, most of your time will probably be spent on the base. Our 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 is a triangle piece of wood at the bottom of the base, the top is capped by the 2" pipe flange.

2005 Events

I was so pleased with the performance of this pipe mount, I decided to make another for Bill's 4" scope. First, I tried to make it out of 1" pipe. That didn't work. As time went on, the scope became harder to turn. The joints were either too tight or too loose. Not enough surface tension and too light a scope. Admitting to the mistake, I replaced all the 1" pipe/flanges with 1.5" pipe/flanges. The results were better, but still not acceptable. I now think Bill's scope would work better mounted directly on a camera tripod (see Practical Telescope #2.5). Pipe mounts work best with long focal length Newtonians, with heavy tubes, like the club's 6" scope.

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This web page was last updated 11/03/10