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Polishing Query

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Posted by Ian McKernan on July 18, 2002 08:07:59 UTC

Hi all!
Ive now got my 10 inch pretty much polished, (at least the surface looks good!), but it has a funny shape. I put it on the Ronchi tester at our group session last night and after everyone had a look the main reaction was, "How the hell did you get something that looks like that!!!" The shape of the bands was likened to an "impact structure". I will either have to fix this or endure the good natured ribbing of friends forever!

Anyhow, ive done some more polishing on pitch, MOT and been playing around with "RonchiZ".

Ive managed to draw a profile in this program that gives me a good simulation of what i'm seeing through the tester at the moment.

That profile has a turned up edge, with a raised ridge about 40% out from centre surrounding a central depression.

From the shape of the profile i think that if i get rid of the ridge the hole in the centre won't look so daunting, and the turned up edge i'll get rid of in parabolising. I just want to get a sphere for now. this is complicated by the fact that my glass is pretty thin. I started with 19mm, but after grinding, its now 16mm at the edge.

I'm planning on continuing MOT, with very short W strokes to take it to a sphere. Any advice or opinion about how i might have gotten this shape in the first place would be appreciated.

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