Something strange with the BESS sharpness tester

[WimSpi]

I notice something strange with the BESS sharpness tester

If I put a block of wood on a digital accurate scale, it weighs (for example) 46.5 grams. If I press tara and weigh that same block again, it again weighs 46.5 grams. That's the way it's supposed to be.

But with my BESS sharpness tester (Edge-On-Up PT50A), I measure a much higher value for the same block of wood: 57 grams.

If I repeat the same measurement as described above on the BESS scale, the results vary: 57 grams, 60 grams, 58 grams 74 grams, and so on.

That there is a difference between scales, I can understand, but the difference is substantial. But that the same cube on the BESS scale gives different measurement results, I find strange.

I do have an idea that difference occurs with putting the block of wood on it. If I put it on more forcefully, I get a higher value than if I put it on more subtly.

Maybe I shouldn't think of my BESS sharpness tester as a "scale.

Who can tell me a little more about this

[Ken S]

Wim,

Email mikeb@edgeonup.com. Mike Brubacher is the owner and a very knowledgeable, helpful, and nice guy. I have been a satisfied Edgeonup user for many years.

You might want to check out the edgeonup forum (bessex.com).

Ken

[3D Anvil]

My guess is that the variation you're seeing is a result of the scale's peak weight feature.  If you put a little pressure on the wood block when you set it down, that pressure will be added to the weight of the block.  With a non-peak scale, you might not even notice that rapid addition because the reading will adjust as soon as you release the block.

[tgbto]

To add to it, even if you don't add any pressure, you're always somehow dropping it ever so slightly. So the force needed to accelerate the wooden block backwards is added to its weight, and is kept as part of the peak measurement.

Still, 28 grams is substantial, so if you see this kind of variations even when you very carefully set the block down on the scale, a little explanation might be in order. I assume batteries are in good condition ?

[WimSpi]

Thanks for the inspiring comments. The device is new. I can check the batteries briefly, but I don't expect anything from them.

I myself also feel that the peak load of setting will be the influence. That is remembered and he weight of the wooden block is added to that. If so, then very careful placement of the blade on the wire is very, very important.

I will email Mike Brubacher as Ken suggests.

[tgbto]

If so, then very careful placement of the blade on the wire is very, very important.

Well it is, but mostly if you don't want your reading to be false because of the sampling frequency.
But as you are measuring the force that causes the wire to break, it doesn't matter if that force is caused by just the pressure of the blade or a slight deceleration as well.

[WimSpi]

This is an answer I got through BESS's forum (see Ken's post above):

"Attempting to place a weight on the tester by hand without influencing the tester is almost impossible.  If the object is released above the pressure plate, even by a tiny distance, so that it falls onto the pressure plate the displayed force will vary from the resting weight of the object.  If the object is pressed onto the pressure plate, the displayed weight will vary from the resting weight of the object due to the influence of your hand."


It matches with previous responses above.

Now I have repeated test and when I very, very carefully put a block of wood on the BESS tester it practically matches the weight measured on an accurate kitchen scale.

If I repeat that on the BESS tester, so very carefully placing that block of wood, the measured values are not much different.

In itself, this is a good exercise to see for yourself how carefully you have to handle the knife on the BESS tester for a good measurement. I did look up at that. Instructive for me.

Thanks for thinking with me!
Wim

[WimSpi]

Today I received some additional information from the BESS forum, about what happens, when you use the BESS tester. This I would like to share with you:

"So what does this mean when taking a sharpness reading? 

Let's consider a 150 sharpness edge.  Imagine that while taking a sharpness reading you get bumped causing the tester display to jump to 25g.  Do you need to tare the scale and start over?  No!  Because with a 150 sharpness edge, 150g of force is needed to sever the test media.  Simply continue the test until the media severs.  In this instance as force is applied to the blade the tester will display 25g until the applied force exceeds 25g at which time the tester will display the new greater force.

In other words you could start a test, get half way through, go to lunch, come back and continue the test.  The only thing that matters is the amount of force applied to the test media by the knife edge when the media severs.  That force value is the sharpness reading and what will be displayed on the tester.  "

Greetings, Wim