Thread: Standard Reference Material for Hanging Hair Test

I have two razors (both Fermaruds) that are clearly not shave ready yet, despite my first attempts at bevel setting and polishing. They both tug severely in shaving.

I have two more razors that shave acceptably well (a Fromm 72R and a Damisons).

I also have a new Supermax DE blade held in a hemostat to simulate a razor.

In my version of the HHT using my wife's hair, the DE blade cut hair easily 4 of 5 times, with one time failing. The two acceptable razors cut hairs in most spots along the blade. The two duller razors cut hair only occasionally only at a particular point on the blades. Thus the HHT correlates well with my idea of shaveability. (I strongly advise people who use the HHT to test their procedure on a new DE blade to calibrate what "sharp" means.)

I made my first crude test jig yesterday. All it was was a piece of 1x4" wood with a 2" equilateral "V" cut into the top and two 7/64" holes drilled 3" apart across the "V" on the top edge. One inch down on each edge I drilled a 7/64" hole on either side. The 4x4" chunk stands on its unmodified edge.

I put two small iron nails into the top holes as capstans, and used the side holes to pin in the thread with matchstick shafts.

The thread used was Danville's fly tying monofilament (0.006"), which acts close to what a coarse human hair does with razors. I chose this thread for several reasons: 1) monofilament, with simple surface structure; 2) diameter within the range of human hair, so relevant; 3) cutting force roughly similar to human hair; 4) commonly available and cheap. The only problem with it is that it's clear, so it's hard to see and therefore work with.

I pegged down one end of a piece of filament in one side, looped one full turn on the first capstan about 3/16" up from the wood, crossed the gap taut and did a corresponding loop on the same side of the other capstan, and then down to the other hole and pegged. The filament does not touch the wood even during the test.

I kept the filament taut rather than slack, mostly because it was easier to do.

I placed the block on my 400 x 0.01 g Ohaus digital scale. The Ohaus appears to update about once a second. I tared with the block and then pressed each blade down perpendicular against the filament as slow as I could.

The DE blade averaged about 12 g force. The Fromm about 14 g and the Damisons about 17. The first Fermarud as 25 g and the second 28. The results seemed more consistent at the higher end than the lower, perhaps because of the suddenness of the breakage.

From this simple pilot project I learned several things:

1. The usual HHT is qualitatively useful, particular with the comparison to the DE blade.

2. The FCT quantitatively supports the shaveability and HHT results.

3. My honing skills are not as bad as I thought: The Fromm is close to the DE sharpness.

4. The quantitative measurement of sharpness does not appear to be difficult to carry out.

5. I've got the right filament to use in testing.

The next step is to automate the test so that constant deformation rate occurs, as opposed to trying to maintain this by hand. And to use a force gauge that returns peak force, rather than trying to catch it on the scale.