Surface Finish Requirements 12-16uinch

[tha89sx]

I need to have a 3/8" round bar finsihed with a surface finsh of 12-16 microinches. Is this something that is going to be achievable using 8620 or 4340 without being heat treated and being ground. The part would be machined on a lathe.

Is there a rule of thumb on what surface finish is possible according to the hardness. Or are the two related?

 

[mrainey]

If it's one piece, you might turn it slightly oversize and polish to get the finish. For a production run, I think you'd be better off adding a grinding operation.

Software For Metalworking

http://closetolerancesoftware.com

 

[CoryPad]

Hardness and surface finish are not related. Those two alloys can achieve the stated roughness.

 

[tha89sx]

CoryPad, the surface finish is more related to the material composition rather than hardness, correct?

 

[unclesyd]

To get that type finish you should start with a clean steel. A common name in the trade is Aircraft Quality especially with the 4000 series materials.

Could you start with a TGP bar like Mirraloy from Associated Steel. We used this material in place of a 4140,4130,3140, along with 4340 on some parts.

http://www.associatedsteel.com/pdf/09-10.pdf

 

[CoryPad]

No, the surface finish is a function of the manufacturing processes.

 

[mrainey]

This chart should help you with surface finish calculations for turning.

http://www.kennametal.com/images/pd...working/noseRadiusSelection_SurfaceFinish.pdf

Software For Metalworking

http://closetolerancesoftware.com