With the addition of a new, computer assisted aiming, night sky catalog, modern telescope, I thought I'd share how my first telescope came about. You may remember the black tube, wood tripod deal I used to have. Here is the story.
It was in 8th Grade at Jane Adams Jr. High, where in science class, the teacher had the idea to do a section on telescope making. Several of us, I think maybe 8 purchased a mirror grinding kit and went to work. We did the grinding after school. Back and forth with first coarse, then finer grips of abrasive. What you do is have the target glass and a tool glass of the same size. YOu do back and forth motions grinding the grit in between the glass blanks, while slowly walking around the work to even out the shape. The tool becomes convex, and the target becomes concave.
We worked with our little containers of grit, once in a while measuring the focal length of the mirror. You do that by getting it wet, and focusing a light with a sharp edge and seeing how far away you needed to get to bring the light into full focus. It's been a long time, but I recall the effect is pretty dramatic when you get into focus. If the length is too long, then it's back to work grinding to remove more glass from the target blank.
Eventually, the estimated focal length is about right, and then polishing begins. Polishing uses a tool of pitch, yeah like from a tree, but refined, that you melt and glob onto your work bench. You set your mirror on top for a rough shape. You use a jewelers rouge that is not at all a grit, but more a polish. The back and forth action does some magic and actually micro melts the glass surface, creating a very smooth surface.
After we judged the mirror to be about right, we sent it out to a company that does vacuum depositing of aluminum alloy on the surface. That metal surface is only a few atoms thick. You get a 'grade' from that coating company. Mine, alas, was not great. It reported that about 30% was not completely polished. None the less, that became the heart of my scope.
I built the tripod in wood shop from mahogany (Legs) and Ash (Top Core). I got chewed out from my shop teacher as I was trying for too sharp a corner on the band saw, and he warned me that I could pull the band off the saw. Didn't happen, but I was warned. Put that tripod together with carriage bolts and a chain. For the scope mount, I used some plumbing fixtures from the local hardware store. A couple flanges and a double threaded pipe nipple.
I built a mirror mount from two pieces of wood, cut into a rough approximation of round. I used bolts though the mirror mount that extended to the second piece that would attach to the tube. In between I used some old car valve springs, to create tension between the two pieces, allowing me to turn thumb screws on the back that were on the bolts to adjust the aim of the mirror. I used some hardware angle irons to hold the mirror to the front mount, screwed into the side of the wood. Real high tech!
The tube for the scope was a 6" aluminum irrigation pipe. I had estimated the length that I needed, but I over estimated and it was too long. Regardless, that's the length of my scope that you may remember. I mounted my mirror and just could not get it into focus. After a long time I dismounted the mirror mount from the tube and had a friend move it up and down the tube, while I looked through the eyepiece to see when something, anything, became visible. Finally, we found the right position for the mirror, a good 18 inches up the tube from my original estimate. So, three more holes drilled and remount, the mount.
I added a finder scope to the top. This is a little telescope to help the bigger scope aim. I used a cheap rifle scope and a mail order set of ring mounts. Again, drilled holes into the tube and bolted those mounts with regular bolts.
I had a working telescope! Easy Peasey!
Dad
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