[ATM] Stupid Fine Grinding Question

[bobmay at nethere.com (Bob May)]

<<
Do you mean short strokes with the mirror on the top or bottom?
I'm working with the mirror on the bottom. Even on the bottom the focal
length kept shortening up so I had to extend the strokes.
After reading your response I believe I have developed two zones with
different focal lengths. I'll go back a number of grits to get it as
spherical as possible before proceeding. I have not made a mirror for a few
years and I must have forgot how.
>>
It doesn't matter which is on top so long as you work that one direction
long enough to finish the shaping of the glass   Doing some grinding with
the mirror on top and then swapping to the other way means that you will
indeed have a deep hole in the center, depending upon the grit size.
You can always force the glass to not grind properly by pushing on the edges
of the item on the top as it is the force on the junction between the two
surfaces, not actually which is on top, that causes the shape to happen
which is why you are probably getting the shortening of the FL even though
the mirror is on the bottom.  Push down evenly over the tool and the
curvature should even out.
Bob May
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bobmay@nethere.com
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