I used NEWT 25, a freeware program available here at Steven Tonkin's website to design the optical part of the telescope, as the image shows. This is a wonderful program that will let you lay out all of the parameters for your scope, and see how everything fits together optically. Highly recommended!

The base is made of the two pre-cut 18-inch MDF circles. I cut MDF sideboards that mount on top of the base, 24 inches high and 13 inches long. Two cross-braces made from the MDF cross the sideboards, one large one at the front and a small one at the rear to provide stability. An M10 shoulder bolt, 3 inches long, goes through a center hole drilled in the two base circles and acts as the azimuth bearing. A 33 RMP record goes on the bottom of the top base circle, and three large magic sliders at 120 degree angles are attached to the bottom base circle just inside the diameter of the record. The record sliding on the magic sliders provides a very smooth motion in azimuth. I cut a U shaped notch at the top of each sideboard for the altitude bearings to ride in. You can see in the side view how the tube in its rings, with the altitude bearings attached to the sides of the rings, rides in the mount. The planning was all done, it was time to start building.

Why Am I Doing This?

The most important thing I can tell you is that this project ended up taking about five times longer than I thought it would! One reason is that I would start to make a part, suddenly think of some tweak-o refinement, and go all the way back to the beginning again which is not the most efficient way to work. But in any case, there were just a lot of small snags to be worked out, and little time-consuming details that needed attention. It took time.

What this means is, you need to have a very clear reason up front why you are building your own scope, instead of just ordering one of the perfectly fine commercial ones out there. If you honestly include what your time is worth, pound savings alone will not be enough of a justification for building your scope from scratch.

Take a hard look at what's available in a 6" dobsonian from Meade, Celestron or Orion (all are under Ł300).

However, some people who are handy with tools just enjoy the satisfaction of putting together a nice project. Some people may have time to spare, but need to save every last penny they can. And some people may be looking for design features that simply can't be found in commercial scopes.

Some Expensive Chunks of Glass !

While it is a time-honored amateur tradition to grind your own mirror, I regret to say that these days, there is not much of a monetary incentive to do it. If you add up the cost of the blank, tool, abrasives, pitch, then the cost of having the end result silvered, you get perilously close to, or go beyond the price of a finished commercial mirror.

Furthermore, there are many hours of strenuous work involved. And the chances of botching the job (or giving up in disgust) are not insignificant. I think I would only consider grinding a mirror myself if, a) I could get a special deal on some of the materials, b) I knew I wanted to grind more mirrrors later, so the learning experience would be useful and, c) if I had an experienced mirror-maker on hand to get me out of trouble.

In other words, I might want to try it someday but mirror grinding definitely would have been the long way around, just to get my first homemade telescope built.

The tube for the telescope is good old cheap, round concrete forming tube. (This has come to be almost universally referred to as "Sonotube" Ž (a Sonoco product), but is also generically made by other companies, sold under various brand names, and is available at your local builder's supply).

Before I built anything, I decided I wanted my telescope to have tube rings. A traditional Dobsonian telescope has a square box of plywood around the tube, on which the altitude bearings are mounted. Using tube rings instead of the normal box would make the scope much easier to balance (just loosen the rings and slide the tube forward or back in the rings), and would allow me to rotate the tube in the rings to adjust the eyepiece position more easily. Beware though, tube rings made of wood are a lot of work! As you can see above, I cut the rings from my main plywood sheet using my jigsaw. I used the thinnest blade I could find, and cut very slowly and carefully. After they were cut, they still required a LOT of sanding to smooth them out and make them fit the tube perfectly. If you have a router and a circle jig, this would be much easier.

Also in the pictures above you can see the Quick-Tube concrete forming tube I used for the main telescope tube. It's spiral-wound cardboard, about 0.125 inches thick, very sturdy and has excellent thermal characteristics. For my 6-inch f8 scope, I got a tube 8 inches inside diameter, and 50 inches long for about Ł20.

Finally, you can see the two circles cut out of the plywood for the mirror cell. The smaller circle is 6 inches in diameter, and the mirror is mounted to this circle with silicone glue. The larger circle is 8 inches wide, and fits nicely inside the main tube. I based my mirror cell on a design I found on the Internet, with slight changes. Three 6mm bolts pass through and are countersunk in the 6-inch circle, through nuts installed there, and with compression springs installed pass through the 8-inch circle with wing nuts on the other side. These three bolts are used to collimate the main mirror and tilt it to align with the tube and the secondary mirror at the front of the tube. This mirror cell has worked out very well. It's easy to collimate, and once set it holds collimation very well.

The azimuth bearing surfaces consist of magic sliders attached to the bottom round base, and a 33 RPM record that is epoxied to the bottom of the upper round piece. This combination gives nice smooth movement, and once you stop moving, it stays where you put it! Smaller magic sliders went into the U shaped slots that the altitude bearings rest in, to give smooth movement against the PVC end cap altitude bearings. The side boards and cross braces were all glued & pegged together. The whole thing was sanded, painted with a coat of white primer, sanded again, another coat of primer, sanded yet again, then two coats of gloss red paint for the final finish. Finally, I used three door stops as feet on the bottom of the ground board. These are placed at 120-degree angles to make a solid tripod-style mount. The door stops were epoxied and screwed to the bottom board. Being rubber, they absorb vibrations well when the mount is on a hard surface, and they protect the ground board from gettting wet when set up on grass or dirt!

Conclusions

Building your own telescope is truly a labour of love. When all was said and done, I spent almost exactly the same amount as if I had purchased a commercial 6-inch Dob from Orion or Meade, so cost was not the real factor here. I also put in somewhere around 30 hours of labour, spread over a three-month period, so it certainly is NOT easier than buying a commercial scope! What did I get for my money, time, and effort?
First, my telescope is much better than any of the commercial scopes. My tube rings make it easy to balance, something that is very painful or not even possible on the commercial scopes. My mirror cell is better ventilated and cools faster than most of the others. My mount is smoother, steadier, and will last longer than the commercial scopes since it's made of much higher quality materials, not chipboard like theirs. My finder is better than what comes standard with the commercial scopes.

The real difference though, is in the doing. I learned a lot about telescope design. I learned new woodworking and mechanical skills. I learned how to get a good finish on different materials. I learned what kind of smooth motion I wanted on my telescope, and how to achieve it. And I have a great deal of pride, when someone else looks through my telescope and says Wow! and I proudly point to it and tell them...I built that.

After putting everything together, I did a very quick and rough first collimation, then headed outside. Saturn was low down in the west, so I swung over and lined up. Wow!, even with just a 26mm eyepiece (46X) the view was bright, clear and crisp. I threw in the 10mm eyepiece (120X), and Saturn was a glorius sight. Clouds rolled in, so that was all the testing it got for First Light.


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