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How do I avoid pitting when optically polishing 17-4PH stainless steel electroforming masters?

(-----) 2007

I am polishing optical electroforming masters. The masters are made of 17-4PH stainless steel. The master shape was machined and I need to bring it to an optical finish. I started sanding the parobolic shape with 600 grit sandpaper. Then I went to 1200 and then 1500 grit. After that I switch to 3.0 micron alumina powder. Next I go to 1.0 and then .3 micron. At 3.0, I don't see the pits, but when get into the 1.0, I start seeing what I call orange peel. When I look at it with magnification, I see an even amount of small pits covering the whole surface of the master. These pits create what looks like haze on my electroformed parts.

I think it may have something to do with the speed I rotate the master. Or could it be the amount of powder vs wetness? Or could it be bad metal? I have polished masters before and this problem is hit and miss.

Can anybody help me?

Kelly Pichel
Own electroforming shop - Aguanga, California, USA


If this is not a constant problem, maybe its the material. Your polishing sequence looks fine. Try adding an additional intermediate step with 9 or 6 microns. Do not apply too much pressure and add enough lubricant.

Guillermo Marrufo
Monterrey, NL, Mexico

January 2, 2008

Your PAD is not longer the right want.
Change for a hardner (and new one at this stage) and add a coolant (ex water).

Jose Castellanos
- Minneapolis, MN, USA

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