A applaud your attention to detail Mr. Sharpco, and I think Mr. Tman states it well in his reply.
It’s important to understand that the sharpness testers are not specifically designed to measure sharpness in exactly, precisely the same spot on the blade every time you take a measurement. It’s not the goal, purpose or mission of the device. Even with the knife in a vice and jig for lowering the blade there could be a variance in repeatability simply from reloading the test media between measurements.
In most cases, super accuracy in same spot measurement repeatability doesn’t really matter for measuring knife edge sharpness. Remember that that test media is only .009 inch in diameter, so unless for some reason you are trying cut something that small and need it to be in exactly the same area of the blade with each cut, being able to measure that exact same spot again is unnecessary and would not improve the usefulness of the data.
I usually take two or there measurements along the blade. If they are all pretty close I just call it good. Sometimes I’ll get lucky and they all will be within 5 – 10 grams of each other. Other times more, maybe 20. That’s OK for my kitchen knives. Depending on how lazy I feel at the moment, I might even put up with a 30 gf variation and just call it good enough. I'm not all that concerned about the sharpness in one tiny spot on the blade, but rather an indication of how sharp and evenly sharpened the blade is overall. It's also useful to indicate that there is still remaining burr, especially if there is large variation in one area.
Zero out your sharpness tester and using your finger run it up to 30. That’s the amount of pressure difference we are talking about when cutting something. That’s very little pressure. I know I would not notice it or even be able to detect that variation of sharpness when slicing a zucchini, a potato or even tomato.
But that’s just me. I guess it depends on what data you are looking for and how you are going to utilize that data when taking sharpness readings on a blade.
It’s important to understand that the sharpness testers are not specifically designed to measure sharpness in exactly, precisely the same spot on the blade every time you take a measurement. It’s not the goal, purpose or mission of the device. Even with the knife in a vice and jig for lowering the blade there could be a variance in repeatability simply from reloading the test media between measurements.
In most cases, super accuracy in same spot measurement repeatability doesn’t really matter for measuring knife edge sharpness. Remember that that test media is only .009 inch in diameter, so unless for some reason you are trying cut something that small and need it to be in exactly the same area of the blade with each cut, being able to measure that exact same spot again is unnecessary and would not improve the usefulness of the data.
I usually take two or there measurements along the blade. If they are all pretty close I just call it good. Sometimes I’ll get lucky and they all will be within 5 – 10 grams of each other. Other times more, maybe 20. That’s OK for my kitchen knives. Depending on how lazy I feel at the moment, I might even put up with a 30 gf variation and just call it good enough. I'm not all that concerned about the sharpness in one tiny spot on the blade, but rather an indication of how sharp and evenly sharpened the blade is overall. It's also useful to indicate that there is still remaining burr, especially if there is large variation in one area.
Zero out your sharpness tester and using your finger run it up to 30. That’s the amount of pressure difference we are talking about when cutting something. That’s very little pressure. I know I would not notice it or even be able to detect that variation of sharpness when slicing a zucchini, a potato or even tomato.
But that’s just me. I guess it depends on what data you are looking for and how you are going to utilize that data when taking sharpness readings on a blade.