Polishing some More with New Lap

Hello again…Polishing continues. In my previous post, I started polishing with an older lap that had approximately 3/16″ of “Acculap” pitch on a circular 10.5″ plaster tool. Being at least 10 years old, I was suspicious of it’s irregular rotation behavior. This seemed to happen regardless of the position of the center of the lap in relation to the radius of the mirror. Not wanting to waste my effort of fine grinding to this point, I decided to make a new lap, 12″ in diameter, or 3/4 of the mirror diameter (seen in this image here). IMG_0001Plaster was my preferred choice for the base material, and “Gugolz” No. 64 pitch was for pitch in lieu of using the “Acculap”. Once the plaster hardened, I used a circular template to locate the center of the lap. I then took a spade bit, as I’ve done with the older lap, to drill a hole large enough to glue in an iron pipe nipple. This will be where the guide shaft will ride and allow the lap to spin while the mirror turntable is rotating. The total polishing time as of this post is only about two hours and already I am seeing a polished surface. Checking this with a laser, there are still areas in the center and about 1 inch of the outer diameter that does not allow the laser to pass through. I am concerned about some unevenness about three inches long on the edge that has not polished out similar to the remaining edge of the mirror. I’ll have to watch this area closely. The laser test I am using to check polishing quality is a simple test using one you can buy for your key chain available almost anywhere these days. The laser works well because it is a very intense light (in my case a common red laser) of a single narrow frequency. Directing the laser on the mirror surface in a darkened room, it becomes very clear where additional polishing is needed or where polishing is not being done on the mirror surface. The ideal situation is when the laser passes thought the polished surface to the bottom surface of the mirror to top of turntable, in effect, showing no reflection. This is a good indication of the mirror having a very highly polished surface and we can now plan to check the mirror for it’s spherical curvature on a test stand. This is an exciting time in the process, when a reflection is apparent, and all the hard work of getting to this point pays off. I will post a discussion on that stage of the manufacturing process when I get there, but for now, it is still more polishing, polishing, polishing…Stay tuned.

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