New Year New Stage, Polishing

IMG_0061With the winter Vortex dominating the continental United States and an estimated 200,000,000 million people affected, I, like many were preoccupied with these events, and distracted from my important task of making the mirror. So with that behind us, I had to figure a way to start polishing the mirror. The stages of using 25, 9 and 5 micron went well, and my spherometer readings were very consistent. After about 4 hours of fine grinding between all of the fine grinding polish sizes, I decided to move on the polishing. I had not a lap to use, except one that was about ten inches in diameter, and sitting idle for probably six years or more. The lap was made using Acculap that came out few years ago, synthetically manufactured. I did not know what the hardness was but thought I would at least get started with polishing using this lap. It also did not have a center pivot point using an iron pipe nipple to allow me to use on my machine. I dealt with this by drilling a 1.25 inch hole in the center with a spade bit on my drill press, inserted the fitting in the hole and glue it in place with “Gorilla Glue”. It worked quite well. Unfortunately, however, this lap was not as circular as it should be, and determining where the center was to drill the hole was at best an estimate, and no matter where it was, there would still be uneven rotation when used with the machine. So with what I hoped was a good lap to complete the polishing stage, I first heated it the oven for about fifteen minutes, hot pressed it on the mirror for 6 hours with zirconium oxide slurry. Then I placed the lap on the mirror at a point where the center of the lap was at half the radius of the mirror or about four inches from the mirror edge (for a 16 inch mirror). This left me with about a 1.5 inch overlap on the mirror. I also moved the machine indoors. fortunately I built it small enough to fit through the garage access door, which I believe was about 28″ wide. Once polishing, I noticed an erratic turing of the lap on the mirror. I was hoping this would smooth out eventually, but after about an hour of polishing, no dice. Interestingly enough, with the lap in the position, it even had a tendency to rotate in the opposite direction slightly for awhile. Based on this observation, it appeared the out of roundness and in-precise location of the center of the pivot point on the lap, created an uneven motion of the lap. But after this short time, I still have partial but uneven polish as shown in this image. Looks like I will be making another lap, round with a fairly accurate center pivot point….

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