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Made a Nimrod this vinter. Ejvind Jensen. Nyborg Denmark.

I had a chance to talk with an abrasives manufacturing engineer about 3M cubitron. It is a ceramic grit. It goes onto the paper as tiny cubes. Each exposed edge is a cutting edge. As it is used the cube breaks along micro fracture lines and a particle breaks off. The newly exposed edges of the break form new sharp cutting edges. Cubitron is sometimes referred to as self-sharpening. The sandpaper will remain sharp as long as there is grit on the paper. In contrast, aluminum oxide, the most common grit, will wear smooth and lose its bite even while there is grit remaining. Cubitron requires pressure to fracture the ceramic grit and renew the edge. It is for power sanding only, not hand sanding. A random orbital sander works fine. I asked about non-clogging paper. Most sandpaper advertised as non-clogging is "open coat" sandpaper where as much as 50% of the paper is not covered with grit. The spaces between the particles shed the residue. Some non-clogging papers have two layers of grit. The base layer is closed coat, completely covered, and the second is open coat and designed to wear off as it becomes clogged. I asked about epoxy. The clogging problem, as we know, is from not letting it cure. If the paper clogs with epoxy it is actually buffing the surface, not abrading it. "If there is no dust you are not sanding." Finally I asked about which sandpaper to use. The answer was that for the home project just experiment and see what works best. Industrial users know how many board feet they are sanding per minute and how many total board feet they get per belt. The differences between grit, adhesive, backing and cost become apparent. The home woodworker isn't fine tuned like that.