3M PSA (pressure sensitive adhesive) backed lapping film 0.3 micron pack of 5 sheets
Sheet size: 8-1/2" x 11" (216mm x 279mm)
Mineral: Aluminium Oxide
What are film abrasives?
3m film abrasives are made from heavy duty cellulose type film (like the stuff used on overhead projectors) coated with micron graded abrasive particles and then flooded with resin that keeps them in place. The reverse side is covered with pressure sensitive adhesive - a heavy duty version of the stuff on the back of a post it note.
3M film abrasives are available in either silicon carbide or aluminium oxide. Silicon carbide particles are sharp brittle shards (similar in appearance to splintered glass); they produce a very fast cut initially and the abrasive becomes progressively finer as the shards break down. Aluminium oxide particles are more like jagged rocks, you don't get that initial incredible performance but they just keep on cutting.
Lapping Film vs Microfinishing Film - what's the difference?
3M lapping film is a very close tolerance abrasive used to produce the finest possible surface. They use colour coding rather than writing on the back because the ink has sufficient thickness to be significant when using the finer grades. Available from 40 micron down to 0.3 micron (0.3 would be the equivalent of a 35,000 grit waterstone - except the particles on lapping film are more consistent so the finish is actually a bit finer).
3M microfinishing film is a heavier duty version, thicker film, heavier resin, coarser grits, longer lasting. This one does have the grades etc written on the backing because it is only available down to 9 micron and at that level the thickness of the ink isn't relevant. Available from 100 micron down to 9 micron.
How is it used?
Most of our customers use it for sharpening woodworking tools, but it's also great for straight razors, knives etc. You cut the A4(ish) sheets into strips, stick them down to a bit of float glass and away you go.
Coarse microfinishing film is great for grinding back primary bevels, reshaping blades, repairing damaged edges etc. In about a minute you can give a chisel a big beard of iron filings and get it warm enough that you can't hold it - it's that fast!
The finest grades of lapping film will give you the sweetest edge you can possibly imagine. Where you choose to switch from MF to lapping is up to you, but it is important to work through a series of grades, completely replacing the scratch pattern from the previous grade each time. It works best with a honing guide, using pull strokes only on anything finer than 60 micron so that you don't plane the film off the glass. By using secondary bevels you can target just the mm or so of steel adjacent to the edge.
How long does it last?
Ages, I cut the sheets into thirds and maybe change them once in a couple of months. You don't need to change the sheet just because it has a few little tears in it, any high spots created by going over a tear will get smoothed out as soon as you get back on the flat. You can keep going until it's really ragged looking, but it is worth cleaning the metal dust out of the surface periodically with a bit of Honerite No1 or similar.
How do you clean the glass when replacing the sheets?
If you're lucky most of the adhesive will stay on the film and any spots that remain will come up by blotting them with the sticky bit on the old sheet. If you end up with a lot of glue on the glass, scrape it off with a chisel and then wipe off any remaining marks with a few drops of orange oil.
What are the equivalent waterstone grits?
It's not a direct comparison because micron grading is so much more accurate that grit / mesh etc, but for a broad comparison there is a conversion chart over on the Workshop Heaven blog.
Can I mix and match the grades when I order?
Sure, please send us a message and let us know which grades you would like.
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On 13-Aug-14 at 18:49:44 BST, seller added the following information:
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