Thread: HHT off the Coticule

Originally Posted by dylandog

The HHT tells you that your razor is sharp. No dull razor passes it.

But it does not tell you that your sharp edge is a smooth edge, and you need a smooth edge for a nice shave.

What's more, failing it does not tell you that you've got a dull edge. Weirdly, a very sharp but smooth (non-toothy) edge can fail it. Enter the coticule edge. Someone with better science can say why this is so.

The HHT is just one ballpark indication among several. Between my wife and me we've got a lot of variation in the hanging hairs around this house, and I personally find the thumbpad test and a modified version of the armhair test (holding the razor very gently, very slowly, against one arm hair, a centimeter away from the skin, to see if it pops without pressure or leverage) more helpful. But you'll often hear from guys here that the only real test is the shave test, and they're right.

I believe it is because, just like we use knives with serated blades to cut through bread, the fine teeth act like a hacksaw through the hair.
The microscopic teeth are so close together that when we push downward on the HHT, we aren't pushing in an exact 90 degree angle and therefor are creating this hacksaw movement on the hairs.

Often burr left on an edge can make it fail the HHT. Best to run the blade through cork prior to honing to get the best results.

Just my scientifically minded opinion of course.

Graham.

The modified armhair test, as Dylandog put it, is far more reliable. In fact, if you wave your razor a centimeter away from your arm over your armhair and you hear a quiet raspy sound and the razor effortlessly pops (catches and cuts) all the hair in its path, it is almost certain to be shaving sharp. It may not be smooth enough, but is usually within 2-3 more strokes to being properly honed.

You have to pay attention to the quality of the cut though - a lot of razors will catch the hair - including grossly overhoned ones, and even ones honed on a 2K stone. It is the quality of how they cut the hair after the catch that is an indication of shaving sharpness. A properly honed razor will cut the hair effortlessly, without bending the hair, without splitting it lengthwise, without pulling the follicle and without much noise, just a quiet pop.