Letter 20052

Machined surface roughness of aluminum for brushing

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I want to have machined aluminum parts(5052 or 6061)given a brushed-satin finish. Is there a surface roughness specification that the machined parts should have prior to brushing?

Robert L. Denningham
- Crofton, MD, USA

Hmmmm. You know, a brushed finish is just that. It does not have any specifications. You can have a rough brushed finish or a smooth brush finish. Without surface finish requirements, you can control either by your brush or by the machining operation.

AF Kenton Nova Finishing Systems Inc. Huntingdon Valley, PA

Thanks to A F Kenton for his reply. I was looking for a numeric specification for a machine shop drawing to avoid the ambiguity of specifying a "smooth" surface. It appears that a roughness average (Ra) of between 20 uin and 30 uin will do it. Several machinists have also told me that if they know the machined parts are to be brushed or "silk-ened" they could machine a suitably smooth finish.

Thanks again.

Robert Denningham
- Crofton, MD, USA

Interesting comment. Different strokes for different folks. This is like going to a different country. Terminology usage changes slightly between differnt groups. The Ra you mentioned is basically that of raw material from the mill, so if that is what you are starting with, then the brushed finish is only for aesthetic reasons and not for surface modification.

AF Kenton Nova Finishing Systems Inc. Huntingdon Valley, PA

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