Polishing 347 Stainless Steel Samples

My experience of machining and hand-polishing a block of stainless about 250mmx150mm is that it's an absolute bitch. My theory was that the darned stuff responded to abrading or burnishing by getting harder, and harder , and harder. Then I'd try 'cutting' the top surface off by going back many grades, and lo! for a short while you seemed to be able to work it again. Don't know anything about electro-polishing but it can't be as hard and unrewarding as manual!

I think a little more info might help, re-reading it sounds like you're preparing for tensile testing?. What surface finish are you hoping to achieve? How many of these are there to do? Are they flat?

These coupons need to be polished to near mirror finish (9 microns or less ) for analysis of different coating compounds.Due to the small size of the samples, it is a fairly difficult task to do mechanically.We have tried tumbling with different media types with limited success.

Electropolishing is somewhat like electroplating in reverse. It removes the pointed tops of the irregularities on the surface. The acid bath in which this is accomplished also removes the iron molecules that are on the surface. When done right, you wind up with a more corrosion resistant surface that is brighter than before electropolishing. In order to try to achieve your "near-mirror" surface, you may have to pre-polish using mechanical means with progressively finer abrasives. Of course, this depends on what you're starting out with and the RMS finish you need to end up with. Hope this helps out.

And finally with Optical Grinding Paste -by hand-using Chamois Leather!

WOW! Talk about a "spit shine"

How bout a slow motion rock polisher. Basically a slow moving cake pan with a felt bottom to hold compound. It moves in a horizontal concentric circle (say 10 to 100 rpm on a rheostat). Kinda old school hobbies stuff but pretty hands off. remember to use a pretty viscus compound or water it down takes longer but the compound will push out to the side otherwise. RPM's will be a delicate balance between centrifuging the compound(bad) and being able to move the samples(gotta do that).

Sounds good to me! Build it big enough and we could go into the car polishing business. We'll just load it up, turn it on, and relax with a few brews while it does its thing! Maybe we could make it self-service? Open the doors, customers drive them in, the doors close, customers swipe their credit cards, and away she goes..........

Sounds like a sub-contract job to someone who has some sort of optical polishing spindle to me. You would set up a number of them on a backing, using for instance pitch (bitumen) to hold them in place, 'grind' then polish throught the grades. Unfortunately youd need to start with something fairly coarse using this method, in order to get their faces all sufficiently in-plane. I'd think maybe a couple of grades of alumina would be the thing to finish with.

Sorry, just re-reading this I'm reminded you are already doing this mechanically. Myself, I would get a piece of material (steel offcut or something reasonably rigid - obviously 'rigid' relative to the kind of flatness you're after) and use pitch or wax to secure these samples into an array of a manageable size (100mmx100mm?). Then lap them on a surface plate with some course carborundum, wouldnn't take long to knock them into plane if your backing is flat. Then maybe go on to either a proprietary lapping sheet or make up a pitch lap on another piece of flat offcut. If they're that small you could do 20 or 30 at a time.