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If the diameter before knurling is 80. Is the knurled diameter also 80?

user154844
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    If the knurling does not remove too much material to reduce the original diameter then it will still be 80 – Solar Mike Nov 19 '18 at 21:06

1 Answers1

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Knurling affects the roughness of a surface, but does not affect its diameter much. No material is removed, so for every indentation, a ridge is formed. This has the effect of making the measured diameter using calipers, for example, slightly larger*. If the knurled diameter is an inspection dimension, then you may wish to place a note on the drawing, after experimental verification, to show the QA team what to look for.

Here is a manufacturer's table of expected increase in diameter for various knurls: http://accu-trak.com/technicalinfo/table1.html (thanks to @D Duck)

Remember the primary purpose of the drawing is to give information to ensure it will be manufactured correctly. Both the person machining the turned 'blank', and the person adding the knurl to that will be primarily concerned with the 'smooth' diameter.

*The average diameter actually goes down, since volume is related to radius cubed, meaning the indentations are deeper than the ridges are tall, relative to the original diameter. In reality this is hard to measure, and I've never seen an engineering drawing where the knurled dimension was different to the turned dimension.

Jonathan R Swift
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