Checking and lapping a machine shop granite stone for flatness in millionths of an inch

Snattlerake · Jan 22, 2021

I have been subscribed to Abom79 for years and have thoroughly enjoyed his repair videos.
He is a good man and works his family's shop and also has a shop at home for side jobs.

He has a Starrett granite block like every good machine shop has for setting up and maintaining flatness to within millionths of an inch.

Just leaning on the stone block caused a measuring tool to register!

He took his granite stone to a shop where they can check it and lap it back into the flatness grade it used to be or even better.

This video shows the process they used to achieve this. The payoff is the very end of the video. It is really amazing and it won't disappoint.

O4L · Jan 22, 2021

I was a machinist back in my younger days so I found this very interesting.

I could enjoy doing what he does in this video for a living.

dennishoddy · Jan 22, 2021

I’ve watched that process many times. There aren’t a lot of folks in that business so they draw premium pay.
Life living on the road is the downside. Your not home much.

BrandonM · Jan 22, 2021

A tenth is one ten-thousandths of an inch.

Calamity Jake · Jan 22, 2021

And 50 millionths is half of one tenth
I'm a retired machinist, one shop I worked in a 5 4ft X 8ft surface plates, they were
calibrated once a year and kept flat within 50 mil. overall

Snattlerake · Jan 22, 2021

TWSS said:
A tenth is one ten-thousandths of an inch.

I stand very corrected. Thanks

Snattlerake · Jan 22, 2021

I cannot remember what video it was but there was a man at a grinder shop who was showing the measurement of a vertical cylinder as compared to another vertical measuring device. He showed the light in between the two was turned into blue light because of the very small gap between them. He said the other light frequencies wouldn't pass through that small of a gap.
He also showed that two gauge blocks that are super clean can be "wrung" together and due to the surface area alone will stick to each other and are very hard to get apart. He said they still don't know why the blocks stick together. They think it's the attraction between electrons or a weak magnetic force.

Profreedomokie · Jan 22, 2021

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.

Checking and lapping a machine shop granite stone for flatness in millionths of an inch

Snattlerake

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O4L

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dennishoddy

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Calamity Jake

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Snattlerake

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Profreedomokie

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Checking and lapping a machine shop granite stone for flatness in millionths of an inch

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