Here are some of the lessons I've learned in doing my mirror:
- Pay very close attention to stroke length. I think
that my Turned Down Edge came from grinding with incorrect stroke
length. I've definitely learned that an ounce of prevention is worth
more than a pound of cure on this one!
- Not all grit is created equal. My 120 grit had some bigger
particles in it, that kept creating small pits in my mirror. A good
way to determine if this is the issue, is to grind a little on some polished
glass, and see if it happens there, too.
- Soft pitch can cause a Turned Down Edge (TDE). If the
pitch is too soft, then the pitch squishes out of the way in the center,
causing less polishing, and the edges that ride over into the air, are
cooled more, so they stay firmer, and polish the edges more.
- Overcorrecting a mirror can happen very, very quickly.
It only took me about 2 extra minutes, of trying to make my mirror a little
bit better, to cause a situation where I have to back way up, and restart my
figuring all over again.
- Don't let your pitch lap get too dry while figuring. A
few seconds of polishing with too much drag on my mirror caused some deeper
grooves in my mirror that had to be fixed.
- Don't laminate your Couder mask to make it stiffer. I
found that the bending of the laminating plastic where cut by the razor
blade caused bright rings to shine outlining each zone. This made it
very difficult to see the shadows behind it.