The tube thickness is quite acceptable for the concrete form tubes to be used. You do need to reinforce the top of the tube so that the spider doesn't deform the tube tho. I'd not recommend using PVC for a tube because you need to use a fairly thick tube and even then, the tube easily deforms as the plastic is not very strong in the bending of the sheet as the plastic is rather flexible. I've got a scope (8" F8) and the tube is about 50lb and thus rather very heavy and even with that thickness, I still see problems with keeping alignment while viewing.
I've seen a Mirror-O-Matic machine and have worked a little with it and it is a very nice compact machine that will do excellent work to get a mirror done fast. Build it the way that the article shows how to do and after you get it done and see how it works, you can try modifying it to possibly suit your needs better. The max. diameter kind of depends upon how big you build it and I think that the article tells how big a mirror you can swing and I'd suspect from the example that I've worked with that a mirror on the order of at least 16" can be turned without problems. I'll also note that you can scale the machine up without needing to increase the motor size a fair bit without problems as the larger the mirror, the slower it needs to turn to keep from going too fast.

• Thanks Bob - andypod - April 24, 2003 - 09:52 UTC