This blog is mainly about Telescope making, and some things about my politics. At last we finally have a President that can say "Fool me once; shame on you. Fool me twice; shame on me." instead of mixing up with an old Who song.

Tuesday, April 29, 2008

First Blood

Some how, I managed to nick my pinky, and it blead all over the grit as I was grinding the back of my mirror. I was cool out there in the shed, and I was doing this in a sweater, but I don't think you can actually say there was sweat... or tears ... yet.

Still grinding the back of the mirror. Went for two more 45 minute whets. That's about all I can do in an evening before its time to come in for din-din. That includes clean up for the next day.

One thing I notice as I do a whet is that the first one on a clean tool lasts about twice around the barrel, but later ones sometimes only go half way around before I have to re-charge the grit. In a 45 minute stint, I recharged the grit 8 or 9 times. After that point I rinsed the mirror and tool and swapped them so that the tool was on top for another 45 minutes. When I had the tool on top, I did a wv pattern, that is, 5 times across from left to right, then turn the tool ccw a little, and then the same pattern back, then step cw and turn the tool ccw again. The amount that I turn the tool is about the same as I step, about 20 to 25 degrees. I have 4 cleats around the perifery, and it takes 4 to 5 steps per quarter.

At the end, at least the marker lines on the mirror were gone, and all the concentric molding marks except for one rough area. I'll give it another couple of hours tomorrow.

One thing I noticed, that even with as little as I did yesterday and today, (3 hours total) the back of the mirror is already concave, and the tool convex. I don't know how that happened, since I gave them equal time on the barrel. The sagitta is about the same as half the thickness of a box cutter blade. I need to find out from someone how to get that flat.

More next time

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