Telescope Mirror Edging
The biscuit cutter method of cutting a mirror from a piece of glass often leaves the mirror's edge in an unsatisfactory state. The following problems might exist:
- The method tends to cut more at the top of the edge than at the bottom with the result that the edge is not square.
- If the mirror is not square with the cutting axis of the machine the cut will be skewed resulting in a slightly elliptical mirror. The skew cut causes the cut to break through unevenly with the result that a rim is left on the one side. It also causes the edge angle to vary around the mirror.
- A rim on one side of the edge where more glass is worn away. It may be a few millimeters deep along the edge and as much as a millimeter deep diameter wise.
These problems needs to be corrected.
One method to correct the edge is to put a thin plate band around it and feeds abrasives to it while the mirror is spinning.
Firstly the mirror needs to be above the turntable of the machine so that the band would be able to cut the whole edge. Make 4 pieces of wood about 8 mm thick
Cut a piece of thin plate, say about 1.6 mm thick, long enough to go around the mirror and