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The Water Cooler
General Discussion
Checking and lapping a machine shop granite stone for flatness in millionths of an inch
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<blockquote data-quote="Profreedomokie" data-source="post: 3506268" data-attributes="member: 524"><p>The shop in the refinery I retired from had a pink granite stone like that. At one time we used to rebuild mechanical seals that are used in pumps. The seal faces had to be so flat they could only be measured by light bands. You had to lay the seal face up side down and lay an optical glass on the seal face. It was lit up with a monochromatic light above it. You would move the glass around to get the air out. The face would have lines across it that were the light bands. If you put a straight edge like a 6" scale on the glass and more than two lines (bands) were crossed it wasn't flat enough. Then it was back to the lapping steel that was impregnated diamond lapping compound and work on it some more. I have no idea in millions of an inch how flat this had to be but, it couldn't be measured by mechanical means like the guy in the clip was checking the stone.</p></blockquote><p></p>
[QUOTE="Profreedomokie, post: 3506268, member: 524"] The shop in the refinery I retired from had a pink granite stone like that. At one time we used to rebuild mechanical seals that are used in pumps. The seal faces had to be so flat they could only be measured by light bands. You had to lay the seal face up side down and lay an optical glass on the seal face. It was lit up with a monochromatic light above it. You would move the glass around to get the air out. The face would have lines across it that were the light bands. If you put a straight edge like a 6" scale on the glass and more than two lines (bands) were crossed it wasn't flat enough. Then it was back to the lapping steel that was impregnated diamond lapping compound and work on it some more. I have no idea in millions of an inch how flat this had to be but, it couldn't be measured by mechanical means like the guy in the clip was checking the stone. [/QUOTE]
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The Water Cooler
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Checking and lapping a machine shop granite stone for flatness in millionths of an inch
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