The 3M corporation manufactures
a wide variety of abrasive sheets with different types of backing, bonding,
and abrasive for all kinds of specialist uses. Woodworkers have embraced the
use of these sheets for the "scary sharp" sharpening system, in which you attach
sheets of sandpaper to a flat substrate (usually 1/4" or thicker glass) and
sharpen away. The main advantage of the "scary sharp" system is its flexibility.
It's also a great way for novice woodworkers to be able to sharpen anything
without making a large initial investment in sharpening stones.
We've carefully chosen particular films for maximum efficiency of use. For more information about our selection of films, please click here. Based on the recommendations of engineers at 3M and some of our own testing, we put together a selection of abrasive sheets that, while not the most inexpensive available, are easy to use, cut the fastest, and last the longest. We offer 3M Imperial Microfinishing Film and 3M Imperial Lapping film. Both of these products were designed for industrial applications and are not readily available. These films use a high strength polyester film as a backing material. The abrasives are carefully graded and electrostatically oriented for greater cutting efficiently. Even grading is very important for even cutting. You get fewer scratches, and more particles of abrasive at the same grit mean that more of the sheet cuts at the same time - faster and more evenly. Unlike more common Wet-or-Dry papers, these papers are designed for cutting metal and have the grit anchored in a layer of resin. The resin holds the grit to the paper in a very strong bond. You'll notice how much longer they last than regular grade papers. Where possible, we stock the film Type P, which has the hardest resin bond for the longest lasting paper. The abrasive is actually embedded in the resin, so while the film feels sort of smooth to the touch, as the resin wears away more, sharp, abrasive is exposed to the steel. All our films are 3mils thick (.003") to make the film less prone to tearing.
One of the most important things to bear in mind with "scary sharp" is that the paper must be fastened flat to a surface. Taping the edges down doesn't work - the paper bunches up in front of the cutting edge, making the paper prone to grabbing and ripping, and also potentially rounding the cutting edge - so most users either use pressure sensitive adhesive (PSA) backed abrasive paper or spray a can of pressurized rubber cement on the substrate and then you pop a plain sheet of abrasive. We sell both PSA and non-PSA film; the descriptions of each product below can help you decide which one is right for you. For either type of film we use alcohol and a razor to clean up any glue residue.
The silicon carbide films we offer cut faster than their aluminum oxide equivalents, although on the very finest grits both the 1 micron and the very fine .3 micron aluminum oxide sheets will leave a better edge. In general, a good sequence of sharpening is 15 micron (similar to a 1200 grit waterstone), followed by 5 (similar to a 5000 grit waterstone), followed by either the 1 and/or the .3 Micron Aluminum Oxide (similar to an 6000 or 12000 grit waterstone respectively). We use the 40 micron size (similar to a 400 grit waterstone) for really rough blade shaping and doing the backs of old blades when we first get them. Typically, shaping and forming the wire edge of the blade is done on the courser grits, so by the time you switch to a finer grit, the blade really just needs a few strokes. Therefore, the coarser grit sheets get used up faster than the fine grit sheets.