[ATM] Nearly polished...but...

["Francis J. O'Reilly" <foreilly@verizon.net>]

Norman,

Glad to see that you are making spectacular progress.

What type of glass are you using for the mirror substrate?

I hope with your environmental factors you are using a hard lap, Gugholz 73 or the equivalent or harder!

Grooves and microfacets are essential to the polishing process. Without them you will get a really unsatisfactory surface.

My suggestion is to first rechannel the lap by setting it on it's edge and firmly affixing it to something very stable on the edge of a table. Make sure that you have something soft on the floor in case it falls. 

Hold a straight piece of 1/4 inch aluminum with a pair of vice grips and heat it with a handheld torch, the kind that you can buy from Sears in the automotive department with a small can of fuel. Don't forget to use workgloves and eye protection. We were tough in the 70's when I started pushing glass. We didn't use much safety equipment then. That was not very bright of us. 

Hold the aluminum with a pair of vice grips and heat it. Once it is relatively evenly heated, it should take about 20 to 30 seconds, press the 1/4 inch edge of the aluminum into the pitch where the grove should be. You will be able to do this two or three times before needing to re heat the aluminum strip. The aluminum will melt a groove into the pitch. (Pitch will run off the tool, which is why we set it up at the edge of the table.) In a few minutes you will have new groves in the lap. Make sure that you have something under the lap  on the floor to catch the melted pitch or your wife will shoot you making the need for a twelve inch mirror moot.

Put the lap in cool water and when it cools down, You will notice that pitch has formed ridges next to the grooves. Don't worry, just trim the ridges next to the groove and any other place where pitch has strayed, as pitch will do faster than a Yankee third baseman, with a single edge razor blade.

Now heat the lap in a pail with really hot water and hot press with the mirror, don't forget to microfacet. I prefer to use bridal veil material for microfaceting. Joann's fabrics is a good source, or Michaels. Your lap will be  rerady to use again.

Now, back to more pressing issues. Hyperboloid?

Lap on top, stop putting so much pressure on the back of the mirror when it is on top.

I would go lap on top for an hour to see what that does to your edge and figure. I think you will be pleasantly surprised.

Please keep us posted.

Francis J. O'Reilly

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