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Rough Grinding Leaves Smooth Edge

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Posted by Brian Matthiesen/">Brian Matthiesen on September 6, 1999 02:29:14 UTC

Help. I found that when I rough ground the primary mirror for an 8" newtonian that I had a ring of about 3/8 of an inch at the very outside of the mirror that took a long time to grind. (#80 grit)

Now, I am beginning the initial polishing with #120 I see the same thing happening. After 10 wets, all but the outside 1/2 inch were smooth. Now after 40 wets I am down to 3/8 of an inch ring on the outside edge.

Am I doing something wrong. Bad stroke? I'm using the 1/3 width W stroke. It could take me another 20 wets to get all the way to the edge.

Anyone have suggestions? I am worried that I will have a turned down edge when I test mirror shape.

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