My dead horse again...
Over at CN in their ATM forum I recently posted about deforming from one figure to another (in my case from paraboloid to hyperboloid, but no matter this is just the intro here).
For a long time I've been wondering whether security mirrors (at least relatively flat ones, not domes) could have their mountings removed and be figured/polished to be at least a low power objective. Some of these mirrors are very large, and much cheaper than thicker telescope mirrors- the latter of course being something of a problematic issue. There are 64 inch security mirrors out there for just a few hundred dollars.
Some of these are glass, others are plastic. I'd imagine that although glass might be easier to get a nice polish out of it is just asking for disaster. Plastics have too much play at both the micro and macro level but at least you won't be picking shards out of your toes.
Now we've discussed here in the forums using water jets as a polishing method- could something like this also be used for 'grinding'/figuring of a plastic element? Would a liquid with enough speed/force be able to prevent major gouging of the surface?
There are both thermoplastics (less good) and thermoset plastics (better for stability).
OK, getting past the initial problems (and assuming that proper mounts can be made) what about flexing to paraboloid here? Can it be done with a plastic mirror? Any downsides relative to glass (which of course is stiffer (but Bakelite and similar thermosets (not marmosets)?).
Just feeling about in the dark here....
Jess Tauber
Over at CN in their ATM forum I recently posted about deforming from one figure to another (in my case from paraboloid to hyperboloid, but no matter this is just the intro here).
For a long time I've been wondering whether security mirrors (at least relatively flat ones, not domes) could have their mountings removed and be figured/polished to be at least a low power objective. Some of these mirrors are very large, and much cheaper than thicker telescope mirrors- the latter of course being something of a problematic issue. There are 64 inch security mirrors out there for just a few hundred dollars.
Some of these are glass, others are plastic. I'd imagine that although glass might be easier to get a nice polish out of it is just asking for disaster. Plastics have too much play at both the micro and macro level but at least you won't be picking shards out of your toes.
Now we've discussed here in the forums using water jets as a polishing method- could something like this also be used for 'grinding'/figuring of a plastic element? Would a liquid with enough speed/force be able to prevent major gouging of the surface?
There are both thermoplastics (less good) and thermoset plastics (better for stability).
OK, getting past the initial problems (and assuming that proper mounts can be made) what about flexing to paraboloid here? Can it be done with a plastic mirror? Any downsides relative to glass (which of course is stiffer (but Bakelite and similar thermosets (not marmosets)?).
Just feeling about in the dark here....
Jess Tauber
