16" Grinding Progress

Here I am pushing glass the hard way, by hand. Actually, I have never used a machine of any type, primarily because I don't have room to store one. I am working this one in the sink in my darkroom. I usually walk the barrel but it's been so darn hot here in FL that I decided to take advantage of the a/c!! This is the first truly thin mirror I've worked so it's all new to me so far, and I am learning already. I started much too soon with the 10" tool. Should have hogged the center out with my 4" iron tool to a greater depth first. I'm at the right RC now, 192", but still need another 1.7" to the edge. I'm almost out of 60 grit. Would I be ok to continue on with 80 to finish up the curve to the edge and then proceed on to 120? Also, would I be better off with a 12" or 14" tool once I get the full curve and diameter finished or is the 10" sufficient? I'm still using the carpet to support, but as soon as I can get some of the bubble wrap I may switch to that. The little bit I had to see how it looked wasn't quite enough to give full diameter support.

Walt

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Walt you hang in there! If I had a clue I would give it to you. I don't so all I can do is offer some attaboys and encouragement. I am sure human sweat has to be a not so secret part of the pride you will have in it when done.

Walter,

I am by no means an expert. I made a 10" under the tutelage of John Dobson last year and am trying to finish a 16" thin plain glass mirror this year. Mark Harry has been offering me some advice on this forum. I didn't get the chance to learn much about figuring from John because he all about star testing exclusively and no disrespect to him, but he doesnt explain things too well. Any way, that mirror works great and it was ground from scratch, etc...

The 16" however, I had pre-generated because the thought of hogging out something that big didn't appeal to me. Besides, I think the pre-generation only cost ~$20. With the coarse grinding out of the way, fine grinding was a breaze. I built a 2" thick, 12" plaster tool and its weight did most of the work. I built another 2" thick, 12" tool for a pitch lap and that was a whole different story. Man, that thing liked to grip the mirror. Sometimes I didn't think I had enough strengh to pull it across the thing. Especially in the early going. So if you are breaking a sweat now, get ready to sweat a little more.

Anyway, if I can make one suggestion, it would be to replace the carpet before polishing. I used a plywood top on a barrel and it worked very well thru fine grinding and polishing. I took a couple month break and when I returned, the barrel lid had warped a little and carpet had certainly flattened some. I ended up getting astigmatism after some figuring. I cut another piece of carpet and added it to the first and was able to remove the astigmatism.

Best of luck with the project. Your photos are inspiring. If I have learned one thing about mirror making it is that it is best done with support from others. I don't know what I would do without this forum to read every day.

Clear skies.

Bill