How to sand/polish to a fine finish?

I have two items that I'm working on. One is a .5000 diameter piece of 17-4PH Stainless that is at Rc42. The other is a small flat piece which is 303. I would like to achieve a near mirror finish on these pieces.

I have a sample pack of lapping sheets purchased from J&L. These sheets are plastic backed and the grit sizes are .3, 1, 3, 5, 9, 12, 15 micron and up. I'm using the aluminum oxide sheet, as I have found that the silicon carbide sheets result in stray scratches, so AO is more friendly to the materials that I'm working on.

I've had good results with the round piece on the lathe at slow speed and moving the paper back and forth lengthwise, as a hone would move.

I'm having more trouble with the softer 303 flat surface.

Is there a resource on the web (here?) that covers this operation well?

I've had great results with wiper inserts but aside from that I've had "like mirror or damn close to it" results just by using progressively finer grades of sand paper (up to 1500) and then various grits of rubbing/polishing compounds and buffing it. Some compounds are courser than some sandpaper. Your local autobody shop supply store will have all of this.

i don't know about these micron sheets ...
but this is how i do it ...
start off with the grit you need to remove the deepest scratches ......if this is 180 grit ...then so be it ...

if you've just had to use 180 ...
then move up to 240...........
go over with this until 180 grit scratches disapeer..........

then do the same with 360 ,600,800,1000.and then 1500

then move onto whatever micron sheet is finer than 1000 or the 1500

then metal polish

all the best.mark

I had some stainless that we polished to a mirror finish. Using the different grit paper works best if you use it on a DA sander. After you use the finest grit paper, Use a buffing wheel with polishing compound, it will come out like a mirror.

You might also try alternating directions between grits. Polish one way to start with, and when you change to a finer grit go 90 degrees from your last. It will make it easier to see if there are remaining scratches.

Make sure you clean up your workpiece before changing grit also. You don't want to be dragging coarser grit around under your paper.

Kevin

joeby said:

You might also try alternating directions between grits. Polish one way to start with, and when you change to a finer grit go 90 degrees from your last. It will make it easier to see if there are remaining scratches.

Make sure you clean up your workpiece before changing grit also. You don't want to be dragging coarser grit around under your paper.

Kevin

Click to expand...

Great information, the changing of 90* or as close as you can get will show you the imperfections that have not been removed from the previous work. I will add if you decide to buff it also use the 90* change between each grade of compound. Clean the part well between each compound, rake wheels out between each compound, and for the last 2 compound grades change the wheel and rake the new wheels to fluff them up, keep these two wheels just for those compounds (write on side of wheel with perm marker the compounds used on wheel), or at least for this work piece.

I like cotton or denim wheels, medium density for most work, a nice soft wheel for last compound. Make sure you keep the wheels raked and loaded with compound, if not the wheels will load up with material being buffed and cause many problems.

Hand sanded using progressively finer silicon carbide wet.dry sandpaper up to 8 micron grit, then buffed:



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