# knurlling question



## kd0afk (Dec 26, 2012)

Will knurlling increase the diameter slightly, like 2 or 3 thousands? I have to make something with pyrex and steel and the have to be flush. The pyrex tube is 1.000" dia (25.4mm) and my steel is .999" dia.
Will knurlling the metal "raise the grain so to speak"?


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## dave-in-england (Dec 26, 2012)

It really depends upon the hardness of the steel, the grade of the knurling inserts ( coarse, medium or fine ) and how much pressure and how many repeat passes you do to to get a good sharp knurl.

But you can guarantee that the diameter on an inch bar will expand up to 0.020" or more.

Try turning the bar down by 0.015" ( diameter ) before knurling.

dave


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## kd0afk (Dec 26, 2012)

Increase in diameter is just what i want. I'll probably knurl it and the turn it down to size.
Thanks


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## Tin Falcon (Dec 26, 2012)

> Increase in diameter is just what i want. I'll probably knurl it and the turn it down to size.
> Thanks



IIRC from school knurling increases the size by 0.010 " but your way should work fine. 
and it will depend on the knurl fine coarse or medium. 
Tin


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## bob shutt (Dec 26, 2012)

Make sure you use a straigth knurl. Diamond knurl will not press well.


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## kd0afk (Dec 26, 2012)

Not sure what size. It came with my qctp. I will play around a little.


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## kd0afk (Dec 26, 2012)

bob shutt said:


> Make sure you use a straigth knurl. Diamond knurl will not press well.



It's not for a press fit. Mainly aesthetic.


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## MachineTom (Dec 27, 2012)

Have you measured the glass tube, more than one place? Unless the tube was ground its not likely to be 1.000" I would not be surprised it is .005 over or undersized.


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## kd0afk (Jan 5, 2013)

I placed an order yesterday so we'll see how precise they are.


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## skyline1 (Jan 6, 2013)

Knurling will increase the effective dia slightly in fact it's an old maintenance fitters trick for replacing ball races on worn shafts , simply knurl the shaft very lightly or if it's not too worn a liberal dose of light centre pop marks will do the same thing. It's something of a bodge but there are cases when you simply need to get a machine running quickly and best practice tends to go out of the window.

Regards Mark


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