Quote:
Originally Posted by Orion
Wouldn't the pitch move with the summer heat making the grinding uneven?  |
You can (and will need to) change the hardness of the pitch to suit the temperature. (boil it to make it harder, add turps to make it softer!) The pitch is pretty firm stuff at normal room temp.
Secondly, it's a good idea to do your figuring at least in an environment which matches the temperature that plan to use the mirror. Not such a big deal with low expansion glass, but worth considering.
Finally, a little movement isn't actually a bad thing. It's the randomness of the hand movements that make such fine surfaces, and something machines find difficult to emulate. There should be no great forces involved either - just time and grit.