I recently inherited a nice Orion 10" Dobsonian telescope, but the base had been irreparably damaged. Coincidentally, I'm also going camping this weekend, and someone suggested I bring the telescope along. Thus I needed a base, fast.
The design is simple and based off of the mount that originally came with the base.
Components
1×
4'x4' sheet of something 1/2" thick.
I used expanded PVC foam, but this could easily be made with MDF or something else.
Conveniently, my father fabricates products from sheet plastic for a living, and since I'm lazy, needed this quickly, and don't currently have the means to cut these shapes out, I asked him to laser cut them from whatever he had available. Turns out, this was 1/4" red expanded pvc. Because I needed the pieces to be thicker, he cut every shape out twice and also sent me the solvent required to weld them together.
Here are the profiles for each piece. For scale, the ring is exactly 2' across.
The sides:
The base:
I had the extra first step of solvent welding each of my duplicate pieces together to double the thickness.
I also solvent welded the ring to the base, but this easily could have been screwed instead.
The rest of the base went together by screwing through parts into the edges of other parts. Since I had the through holes laser cut, this was a really fast and straightforward process.
The alt-motion section screwed together:
The alt-section screwed to the az-section:
A view of the bottom. Made sure these screws were nice and flush with the bottom, if not a little countersunk. You can see some holes where I was planning on adding screws, but it turned out to not be necessary at all for stability.
The section above sits and rotates freely in the ringed base created earlier. I was originally going to add a pivot point, but it turned out to be not at all necessary.
Cool idea of putting a base circle inside a ring to limit lateral travel! I've never seen that before, only ever the central pivot bolt. How much space did you leave between the circle and the ring, and does that introduce peculiar slop when slowly tracking through an eyepiece?
I was originally going to put a pivot in there, but changed my mind after I built the two parts because this will be easier to transport.
I left just enough slop that I'd have some wiggle room if things weren't aligned correctly. I think it's 1/4" around the edge. This can definitely be cut down significantly, and if I though ahead, I wouldn't have left any slop (because the tolerance of the laser cutter would be enough at 8 mil all around).
Disclaimer: I've never used a telescope before, so I've no idea what sort of desirable features I should want or need in a base. I can report back early next week with how my adventures go this weekend. Apparently I've inherited an eyepiece rack, which is great, because I have a ton of eyepieces for this thing.
The other thing I noticed about commercial alt-az bases is that they use teflon between the telescope and the supporting v-grove, but then pull the springs down over hooks, using the spring tension to support the weight of the telescope. I can't say that part of the design made any sense to me, so I haven't done anything with the springs yet. The friction of the PVC on the pivot points is enough to keep the telescope from moving when left alone, but not so much as to make it hard do move. I played with it a little, and there was no drooping when set to any angle. I screwed up my dimensions a little bit, so it doesn't go fully vertical, but it'll be an easy thing to fix in a future version. The current dimensions would probably fit an 8" telescope properly.
Ok, I lent it to a friend who's good with telescopes, and here's what he had to say.
"This is clearly a barebones functionality base, but it gets the job done. The gap didn't introduce any noticeable slop, since the lateral movement is negligible over the distances we're viewing. The one issue was that we were using it in a dusty area, and some gravel got in the azimuth part, causing it to bind and not move very smoothly."