"Huge" wrote in message
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On 2017-01-13, Iain Churches wrote:

"Huge" wrote in message
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And they're right. The surface noise levels go up considerably, I assume
because gunge that was previously in the bottom of the groove has now
been distributed over the groove walls.

A peep through a microscope before and after might be
revealing.

"First buy your microscope".

)

I have one from a Neumann disc cutting lathe