3M Lapping Film

3M lapping film is a kind of ultra-fine sandpaper, although the backing is actually a polyester film rather than paper.  I had some sheets in 15 micron, 5 micron, and 0.3 micron grades (a kit for "scary sharpening," available from http://www.toolsforworkingwood.com).  (Actually, I discovered the "scary sharp" system by way of Brent's Sharpening Pages, which also introduced me to the QX3 microscope.) 

I cut some small (1/4" wide) strips of lapping film and applied them to the axles using some honing oil.  After each application I wiped the axle with a cotton cloth, just as I did with the wet sandpaper.  For these pictures I started with the axle that had previously been prepared by nail file and then polished with 2000 grit sandpaper.  The first picture shows that axle again, just before application of the lapping film.

To my eye, it looks to me like the 15µ film makes a worse finish than that left by the 2000 grit wet-or-dry.  Getting down the the 0.3µ film improves the surface compared to 15µ (as you'd expect), but overall it's hard for me to say the surface ends up any better than what the 2000 grit sandpaper left. 

The best reference for grit sizes I have is wikipedia's entry on Sandpaper, but it doesn't seem to describe 2000 grit sandpaper.  That article refers to a sizes.com page that suggests 2000 grit sandpaper has a roughly 1µ particle size already.  So maybe this result is unsurprising. 

Next to try – lapping film with water rather than oil.