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Metal finishing Q&As since 1989

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Machining requirements for part to be electropolished

I have a part which is manufactured from 304L SST. The part requires electropolishing to a 8 micro-inch finish or better. All surfaces will be milled. My question is what should the finish be off of the mill to obtain a 8 or better finish?

Jim Hoffman
- Saxonburg, Pennsylvania, USA
2003

I don't think that it is possible to have a finish fine enough "off the mill" to get electropolishing that fine.

Electropolishing alone doesn't even get that fine unless there is satisfactory surface preparation either through sanding, tumbling, or etching beforehand.

Electropolishing affords between a 4.0 to 16.0 Ra finish in microinches, according to A.S.T.M. specs. Whereas a #8 finish equals 0.74 to 4.0 Ra, and a Super #8 equals 0.4 to 0.8 Ra. To answer your question, possibly a mill finish #3(10.0 to 43.0 Ra) will be fine enough to see electropolishing give you the finish you are after.

Good luck!

Jeff Swayze
- Kelowna, B.C., Canada
2003

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