Multigrit wheel benefits: General Industry Coverage

Dear Doc: I grind tungsten carbide-tipped saw blades and the sales guy is pushing tri-grit wheels. What’s your take on these?

The Doc Replies: They’re great, and here’s why. Tri-grit wheels have three different grit sizes. The biggest grits on the outer edge of the cup wheel and the medium-sized grits in the middle do all the hard work. The finest grits on the inside impart a fine surface finish—but that’s not the real benefit. Rather, it’s how they easily wear. This produces a flat on the trailing edge of the cup wheel.

Figure 1 shows a measured profile of a worn cup wheel at a company I visited that grinds carbide-tipped endmills. You can see that the fine, 1,200-mesh grits wore away and created a flat. That flat, along with the grit size, will impart a fine surface finish. The larger 150-mesh and 400-mesh grits remove most of the material.

In contrast, with only a single grit size, the taper wears more evenly and eventually you are grinding with a point at the inner rim of the wheel—i.e., without a flat—and this produces a poor surface finish. That’s why a tri-grit wheel can work so well.

Dear Doc: I grind cermet-tipped saw blades with cup wheels and notice that the surface finish eventually deteriorates after truing. Somebody mentioned dressing a taper. How does this work?

The Doc Replies: Cup wheels are horrifically maddening. After truing a cup wheel flat, all the grinding occurs at the leading edge. A taper slowly develops and the grinding shifts from the front of the wheel to the bottom. That’s fine, but eventually this taper nearly turns into a point and surface finish deteriorates while grinding temperatures rise.