Edge Sharpness Tester

Did another knife today, this one S110V at 65 RC and .005" behind the edge, used in the kitchen for the past 3 years or so.

Sharpened once then just touched up for the past 3 years on ceramic.

Test 1 - Out of the drawer:

167, 180, 173 = Ave 173

Test 2 - 1,200 grit Ceramic rod quick touch up

99, 113, 110 = Ave 107

Test 3 - SIC on EP 400 grit fast raise a bur and bur removal.

54, 59, 59 = Ave 57

Test 4 - Edge reset using SIC 320 then finish with 400 grit SIC on EP.

44, 48, 47 = Ave 46.3

So what I found in the process over a few knives and steels is that with the 400 Grit Congress stone that I use to finish with will give me Sub 50 BESS numbers without much of an issue, not bad for a 40 Micron stone.

I am happy with that. :thumbup:
 
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Well I got mine in the mail before leaving this morning and only got a chance to test my Leek so far, what I need is a scale that goes up higher than 100 grams. Getting about 150 with that.

I think the whole static load thing is more of an issue than when its within 10 grams as well. Due to the limit of my scale, I am putting a 100 gram calibration weight into a cup and then pouring water until the test media severs, and measuring the the weight of the water plus that of the cup and calibration weight (about 111 grams). I walked to the kitchen to get a cup of water when the 100 gram weight was in the cup and the test media on the knife, and when I got back I poured only a gram or two of water into the cup before it severed. I'd already ran the test a a few times so knew it was the time that it'd taken me to go refill the water. Since I've been getting closer to 150-160 grams needed, it seems that the static load issue is effecting it pretty far outside of 10 grams from the sever weight.

I'm still working out consistency issues with loading the media. If I let the spool "dangle" when loading the media, I get about 150 BESS on the Leek. However if I instead pull the canister down and let it tension enough to draw the spool, I get closer to 100.
 
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KennyB said:
I'm still working out consistency issues with loading the media. If I let the spool "dangle" when loading the media, I get about 150 BESS on the Leek. However if I instead pull the canister down and let it tension enough to draw the spool, I get closer to 100.
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Now that's interesting...!
 
Lagrangian said:
Maybe a dumb question?

I'm curious how the tension of the test thread is set, and how stable that is. So if you set the thread many times, what is the distribution of thread tensions? Or just the standard deviation of the tension. I'm also curious about how sensitive the test is to different thread tensions. So if we ran tests at a slightly higher (or lower) tension, how much does that affect the result?

Originally, I was guessing that the tension would be set by hanging a standard weight on the thread while the thread goes over a bend or pulley, and then is clamped by pincers (that way there is no pulling or pushing of the thread while tightening down a screw or nut). I think this would be a reasonable way to consistently set the tension and take another variable out of the test.

As a physics major, I would guess (without having worked out all of the details), that if the test media were very inelastic and brittle, then tension could matter a lot. This is simply due to the geometry of how a thread stretches when being clamped at both ends and then loaded so that it changes from a straight line to an angle (or v shape). If you are an engineer, or physics major, you can see this is a very interesting problem. (You can analyze it several ways, such as the method of virtual work.) What you would study is how the stiffness of the thread affects the tension of the thread for a given weight. It would be interesting to get some formulas and plots for:

Input:
Thread Tension when unloaded (no load weight)
Thread Stiffness
Load weight

Output:
Thread Tension when the load weight is applied.

Pretty busy, but might be fun to work this out? If you're a technical person, feel free to do so and we can check each other's results, etc.

A couple of caveats: In the above analysis I'm assuming the thread acts like a very stiff spring (linearly elastic). If the thread is specifically designed to be non-linear, then all bets are off (much harder to analyze). But this could be on purpose, as it might improve the tests repeatability (precision).
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Hi Lagrangian!

That seemed to be kind of a sticking point for a lot of guys, so I came up with the cheap and easy solution that KennyB beat me to by minutes.

They have small, accurate spring scales and small clips on Amazon. I like the scale that goes to 250 grams, because I've been looking in the 75-100 gram tension area.

I know Komi's and Ankerson's address, so they will have a chance to test what I'm using in a few days.

I've tested what I have, and it works well.
 
One thing I'd like to see now is a good way to meter shot. It should be able to go from a flow to a trickle.

It's known that this is a time sensitive test. So is a Rockwell test. So are tons of other tests. I don't think it'd be out of line to know how long the test took, and controlled metering of shot would have an effect. I don't mean everyone should pour their shot in the same way, I'm saying right now I'd like some way of making that faster, easier and more accurate. There are lots of times I run over what it actually took.

I'm surprised with the accuracy of the BESS numbers now. You guys have done an amazing amount of fine tuning, and pretty much set the standard by which others will be working toward.
 
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I'm still waiting on the unit, but I'm in no rush.

What additional equipment should I order? A digital scale (that goes up to?), and what else?
 
In some hardness tests, like Vickers Hardness, there is a time limit.

http://en.wikipedia.org/wiki/Vickers_hardness_test
"Vickers hardness numbers are reported as xxxHVyy, e.g. 440HV30, or xxxHVyy/zz if duration of force differs from 10 s to 15 s, e.g. 440Hv30/20, where:

"440 is the hardness number,
"HV gives the hardness scale (Vickers),
"30 indicates the load used in kgf.
"20 indicates the loading time if it differs from 10 s to 15 s"

I forget if Rockwell has a time limit too. Maybe not? Probably a discussion of this is in the NIST handbook on Rockwell Hardness testing.
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=853006

In anycase, it wouldn't be hard to have a timer for the knife sharpness test. I just have no idea how to choose how long the time limit should be.
 
I think pouring water into a cup seems to be the best way to fluidly add weight. There might be a little bit of extra runoff after the cut has been made, but you have to figure with water's density being about 1.5 gram per cubic centimeter, that whatever little bit of extra run-off will only constitute about a gram extra. A full CC of water is fairly large...

I definitely need to get a scale that measures over 100 grams. The problem I'm having is that I'm so close to 100 grams that the media will sever in about a second or so of static load at that weight. Pretty much the amount of time it takes me to put the 100 gram weight on the platen, and then retrieve one of the cups (they're about 10.5 grams) and place it on top. So I can assume that my BESS score is probably 110, but then is that extra 10 grams from the cup really all the extra weight needed or in the time it took to place it there was it far enough into the static load to just make it sever clean?
 
Well I'm surprised, out of a little preliminary tries last night it appears my Izula is what I'm able to get sharpest. I wouldn't have expected that one over the Leek given the difference in blade stock.

440C Izula, 20 degree back bevel with 30 degree microbevel ( not sure where to measure thickness behind the edge on this one, but if at the back bevel, it's .035"):
First run without touch up: Avg 200+ ( don't have a proper scale to measure higher )
After touch up on DMT F: Avg 46.3

The Leek I can only manage to get down to 100, even though it started at about 130 the touch-up didn't really help anything. I think it's the edge geometry, since the Leek has about a 36-40 degree edge angle on it. .025" thick behind the edge shoulders.

Gonna try with my Kershaw "Wild Turkey" and my SAK later, as I have very acute angles on these, I'm predicting lower numbers than for the Leek.

I'm still able to produce numbers +/- 10 BESS points simply by altering the way I am loading the test media. I believe the current way is best...

1. Loop media behind screws on yoke, and pull each end down until it is running through the slot cut out of each respective shoe clamp
2. Pull on the media until the spool is suspended upward by it, and fasten the clamp furthest from the media to lock it in place.
3. While pushing the spool down with enough tension to spool more media out, tighten the clamp closest to the media.

I think the key is finding something that's quickly and easily repeatable to not allow deviation to creep in. The good thing is that the numbers are usually so close, that if you do screw up with the screen tension you can probably spot the anamoly very quickly. I ran 5 averages for the Izula, and only one of them was actually under 46, the rest were all 46.x.

Edit:

Oh and can someone with a large-bellied knife confirm this for me? If you place the test media on the portion of the blade that is sloping downwards, does this replicate a slicing cut? On portions of my Izula near the front of the blade ( sloping on the belly ) I was getting wildly different numbers, some as low as 20 or 15, and so I believe it was slicing the media rather than cutting through it with direct pressure.
 
KennyB said:
Edit:

Oh and can someone with a large-bellied knife confirm this for me? If you place the test media on the portion of the blade that is sloping downwards, does this replicate a slicing cut? On portions of my Izula near the front of the blade ( sloping on the belly ) I was getting wildly different numbers, some as low as 20 or 15, and so I believe it was slicing the media rather than cutting through it with direct pressure.
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I haven't had one slip on the belly as I've been doing most of my testing nearer the heel, and making sure the edge is not sloping to either side at the test site when the edge does have a curve. ANY lengthwise movement will sever the test media at very low amounts of force.

Some of my edges would sever it with no additional weight and several slid with some damage to the cord - I arbitrarily put 20g on the platen and every knife I tested would sever the BESS cord within (a guess, it looked immediate) several mm at most. If the cord slides at all during testing I'd imagine a large drop in required force.
 
I just tested out a Gayle Bradley up through a mirror progression. This time, I also compared 12lb fishing line along w/ the BESS media to see what if any difference. This was done on the Wicked Edge at 15 dps and at each grit and with each media I did three tests: one about 1/4"-1/2" up from the heel, one in the middle of the flat part, and one at the beginning of the belly (I did not do any in the belly for fear of altering the results). I also broke it down for you to compare the individual numbers with each other, so in a sequence of x, x, x the each 1st, 2nd, and 3rd spot were checked in the same place immediately after each other. This was done always from heel->middle->belly

200 grit stones, stropped on pant leg - would somewhat shave hair on arm
BESS: 65 average (0 gr spread: 65, 65, 65)
Fishing line: 155 gr average (50 gr spread: 180, 155, 130)
note: so above, for example, it took 180 gr on the fishing line and 65 gr on the BESS cord in the same spot, near the heel of the blade. these parallel each other throughout the progression.

1000 grit NEW stone, stropped on pant leg - would shave a little better than the 200's but not much
BESS: 76 average (30 gr spread: 95, 70, 65)
Fishing line: 175 gr average (60 gr spread: 115, 100, 80)
20150522_152005046.png



1000 grit WELL WORN stone, stropped on pant leg - would pop hairs off of my arm
BESS: 38 average (15 gr spread: 45, 40, 30)
Fishing line: 98 average (35 gr spread: 115, 100, 80)
20150522_150108883.png


Progressed to 3um lapping films, not stropped on pant leg - at this point the edge was whittling hair and severing it some very close to point of hold
BESS: 68 average (15 gr spread: 70, 75, 60)
Fishing line: 193 average (15 gr spread: 185, 200, 195)
20150522_154823895.png


Less than 100 passes on a balsa strop w/ .25 diamond paste - at this point passing HHT-4 all points of edge holding hair 3/4-1" from point of hold
BESS: 63 average (35 gr spread: 45, 85, 60)
Fishing line: 178 average (5 gr apread: 180, 175, 180)
20150522_162631795.png


So, needless to say, I'm still confused :)
 
razor-edge-knives said:
I just tested out a Gayle Bradley up through a mirror progression. This time, I also compared 12lb fishing line along w/ the BESS media to see what if any difference. This was done on the Wicked Edge at 15 dps and at each grit and with each media I did three tests: one about 1/4"-1/2" up from the heel, one in the middle of the flat part, and one at the beginning of the belly (I did not do any in the belly for fear of altering the results). I also broke it down for you to compare the individual numbers with each other, so in a sequence of x, x, x the each 1st, 2nd, and 3rd spot were checked in the same place immediately after each other. This was done always from heel->middle->belly

200 grit stones, stropped on pant leg - would somewhat shave hair on arm
BESS: 65 average (0 gr spread: 65, 65, 65)
Fishing line: 155 gr average (50 gr spread: 180, 155, 130)
note: so above, for example, it took 180 gr on the fishing line and 65 gr on the BESS cord in the same spot, near the heel of the blade. these parallel each other throughout the progression.

1000 grit NEW stone, stropped on pant leg - would shave a little better than the 200's but not much
BESS: 76 average (30 gr spread: 95, 70, 65)
Fishing line: 175 gr average (60 gr spread: 115, 100, 80)
20150522_152005046.png



1000 grit WELL WORN stone, stropped on pant leg - would pop hairs off of my arm
BESS: 38 average (15 gr spread: 45, 40, 30)
Fishing line: 98 average (35 gr spread: 115, 100, 80)
20150522_150108883.png


Progressed to 3um lapping films, not stropped on pant leg - at this point the edge was whittling hair and severing it some very close to point of hold
BESS: 68 average (15 gr spread: 70, 75, 60)
Fishing line: 193 average (15 gr spread: 185, 200, 195)
20150522_154823895.png


Less than 100 passes on a balsa strop w/ .25 diamond paste - at this point passing HHT-4 all points of edge holding hair 3/4-1" from point of hold
BESS: 63 average (35 gr spread: 45, 85, 60)
Fishing line: 178 average (5 gr apread: 180, 175, 180)
20150522_162631795.png


So, needless to say, I'm still confused :)
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What is it you're confused about? The fact that your hair-hanging test edge was higher BESS numbers than others?
 
Josh, I would speculate that your balsa-stropped edge being damaged by the measurement.
Rather than comparing with fishing line, I suggested sewing thread since it should not blunt the highly refined edge.
 
KennyB said:
What is it you're confused about? The fact that your hair-hanging test edge was higher BESS numbers than others?
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Yes

ToddS said:
Josh, I would speculate that your balsa-stropped edge being damaged by the measurement.
Rather than comparing with fishing line, I suggested sewing thread since it should not blunt the highly refined edge.
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That may be true Todd... But I randomly did the bess media and fishing line first, switching up which one I tested first. I did not consistently test one first in each spot. And I did try the thread first actually, but the problem is that it took such low force to sever it I would not have been able to gauge it accurately. In other words, the yoke that holds the media weighs about 50 grams... It would have required less than this to sever sewing thread.
 
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