Best Of

Given the feedback I'm settling in to an idea/device that I am capable of putting together and is cheap. A basic drug dealer scale, synthetic hair, and a pully. I'll basically pull the hair down towards the scale where the razor sits facing up and have a camera recording video as I pull. I can then stop recording when the hair cuts, and review the exact moment on my computer to get the force reading from the scale. It should cost like $20. Scientists could rip this apart, but for my purposes I think it will do. I'll do about 3 runs per blade to get a simple mean of the force required. This along with the microscopic pictures and measurements should cover my mental cost of entry in to the consumer's mind as a legit source of data.

I think you could make a pull test that uses a threaded rod. Requires a bit of doing.

Here's my 2 minute sketch of such a device.

I would actually recommend looking into hardness testing (like a Rockwell test) but utilizing the blade you want to test instead of a hardness testing tool. Basically, you're going to want something that can lower a blade onto a fixed material at a consistent force, or something that can lower a material onto a fixed blade at a consistent force. The issue you're going to run into is equipment cost. If I know whether you're looking into serious equipment or just doing stuff for shiggles, I can make much better recommendations.

There are some materials science problems here which I think I should mention:

1. Spring based force measurement device that somehow is attached to weights or the razor blade and pushes the blade into rayon thread. Jot down the number of Newtons, or whatever, it takes to finally slice through that thread. The lower the force required, the sharper the blade.

Thread strength is dependent on a lot of factors including humidity, age, and thread fiber size which are not easy to control for. Your results will be inconsistent.

2. Use a printer to push paper in to a clamped blade and under a microscope see how clean the cut was on the paper. Sadly this does not result with a number, which would be more ideal.

Paper material properties are similarly dependent on factors you can't really control and will exhibit variation from page to page and also spatially on the same page.

Neither of these ideas are great. #1 is bad because it would be hard to use for comparing different blades. I would need to apply the exact same amount of force, in the exact same increments, and keep blade/thread at the same angle. It's not a realistic experiment without precision machining. Meanwhile, the printer idea although easy to setup for consistency, does not provide a numeric outcome.

What's the objective? From a purely materials point of view, the ability to cut with "sharpness" alone is dependent on the area of the blade in contact with the medium to be cut through the mechanism of contact pressure causing local stresses in the material in excess of its yield strength. This is not the same as a serrated blade where any motion along the blade creates damage sites in the material being cut which greatly reduce the energy required to cut them. Nearly all real blades are serrated from this perspective (scissors and pretty much anything that cuts with any slicing motion) due to inconsistencies in blade edge at both the macroscopic and microscopic level.