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• # Coefficient of friction knurled steel

Discussion in 'Calculations' started by rob_kal, Jun 1, 2014.

1. ### rob_kalNew Member

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Jun 2014
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I am looking for information about coefficient of friction knurled steel. Two steel surfaces but one surface is knurled. I can't find any information. Maybe someone know where i can find it.

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3. ### ErichWell-Known Member

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Feb 2012
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You won't find any information. friction is a property of the materials in contact, not the roughness of said surfaces.

Knurls cause deformations of the material. To cause the parts to move relative to each other the knurls must cause the steel to compress further.

The points of the knurl must slide up the ramp of the mating depression as the outer part expands due to the pressure exerted as the knurls move up the ramp.
It is very complicated, Material hardness of both pieces, tensile strengths, coefficients of friction and lubrication are all at play simultaneously.

This is a great example where empirical engineering will get reliable, believable results faster than theory.

Make prototypes with varying amounts of interference and measure the performance aspects that are most important to you.

4. ### KevinCWell-Known Member

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Jun 2011
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As Erich said, it's a property between materials, not roughness.

But if you still want a very rough starting point. Here is something that you can look at. You said one is Knurled, one is not. So I'd assume the not knurled surface is rather smooth. If that's the case, the equivilant coefficient of friction should be rather similar to smooth steel on smooth steel, may be only a slight fraction higher.

According to engineering toolbox, coefficient of friction of steel on steel without lube is about 0.5-0.8. Since steel on steel is already pretty high. I can probably guess that the equivilant coefficient of friction would fall in between 0.5-0.9 ish range.

Now you'll probably have some rough starting point to start. Hope that it helps.