Revisiting a topic that came up in a different thread. I wanted to know how to tell a dull cutter from a sharp one. I tried a few ways to feel the difference, but I don’t have much confidence in any of them.
The fact that you can “see” the edge is the indication of dullness. When a cutter is brand new the cutting edge offers no reflection, and you won’t really see it at all. The more you can see a reflection or a bright line on the edge, the more dull your cutter is.
In this case, the easiest way to compare is to just look at the tip-end vs. further up the flutes. The cutting edge “disappears” about 50% up the flutes, indicating that it’s sharper for the upper half of the cutter than the lower-half.
Duller cutters have to work more to remove material, but they’re still fine for roughing, especially in softer materials that don’t tear out too badly, such as polyurethane foams/lighter-weight tooling board, and waxes.
You can also frequently get a tool re-sharpened for less than buying a new one, if you have them processed in batches. You’ll still have lost any special coatings, but a sharp uncoated carbide tool still works just fine in much of what we’re cutting around here