Recall that I’m in the process of testing various internet suggestions for ways to extend the life of a razor blade or disposable shaver.
As part of that, I’d like to have some objective measure of blade sharpness.
One way to test the sharpness of a blade is by measuring the force required to cut a wire or thread. The sharper the blade, the less force required.
Commercial sharpness testers using this approach cost maybe $200 and up. That’s a bit pricey, considering that the only use I have for that is to test 10-cent razor blades.
For my initial post in this series, I made my own crude sharpness testers out of washers, super glue, a stout thread, and a kitchen scale. Like so:
Set the washer on the scale, tare the scale, and see how much downward force is required to cut the thread.
For this round, I decided that a) that was too much work, b) it doesn’t yield enough tests per batch, and c) there are easier and better ways to do this.
Here’s the new, improved sharpness tester. The principle is the same as the old one: Make something to hold a thread in place, then cut through that thread while it’s sitting on a kitchen scale. Use the scale to measure the force required.
But:
First, instead of gluing thread across washers, glue thread to a slotted piece of wood. In this case, I’m using a little bit of “fluted” commercial trim, about one inch wide, and about a foot long. Wrap the thread around the trim, spiral-fashion, and glue each piece of thread to the trim. This way, I get about 20 tests per foot of trim.
Second, instead of holding the blade by hand, rig up something so that you get a steadier cut. Here, I’m using a scrap piece of steel, some magnets, a bit of duct tape, and some blocks and clamps to make a long, moveable arm to hold the razor blade above the sharpness tester.
To test sharpness, install a blade, tare the scale, position blade above one of the hollows in the trim, and push down slowly until the thread parts. Try to catch the maximum weight reading on the scale. (If I were totally serious about this, I’d film the weighing so I could rewind to catch the maximum weight. As it stands, I just go slowly and do my best to catch the maximum.)
The exact choice of materials doesn’t much matter. If I hadn’t found that trim, I would have just ripped some slots in a board using a table saw. If I hadn’t had the steel on hand, I’d likely have used PVC pipe and rigged up something for attaching the saw blade. All you’re after is something rigid to hold the thread, and something steady to hold the blade.
This surely isn’t perfect. And the readings in grams are not comparable to what you’d get from a commercial sharpness tester. But this should be plenty good enough to show that (e.g.) the two edges of a razor blade, treated differently, either do or don’t have the same sharpness.
For sure, if my only other alternative for testing blades is to shave with them, or maybe scrape a fingertip over them, then this is a significant improvement.
