Overheated edge BESS scores

[EOU]

Uh-oh. Stones versus belts again. This is clearly an issue of edge rolling. The equipment and instrumentation exists to test both theories and, at the least, confirm or dispute the Kiwi's (hope this is received as a friendly term) findings.

[KnifeGrinders]

Even though I don't own a belt sharpener, negation would have been my first response to that report, hadn't we already got the felt wheel data from the plant. Plus a few months ago I was lucky to meet a boning butcher able to explain his needs clearly even to an arrogant egghead like myself.
All that made me take the edge apex overheating seriously and replace our paper wheel grinders with low speed ones, and revise our deburring technique to reduce risk of overheating.

But what is vital for meat processing, can be ignored for your kitchen knives. In many knife applications that little overheating is of academic interest.

[Bud]

In many knife applications that little overheating is of academic interest.

Very good point KnifeGrinders. At work we may get very excited over 10% one way or the other. At home who cares if one knife edge lasts 10% longer than another? Especially if that 10%  costs you double the price of the knife or three times longer to sharpen.
Posted by EOU - 06-21-2018, 09:17 AM

[grepper]

I completely agree Mr. Bud. IMHO, for all intents and practical real-world purposes unless the edge is grossly overhead by incredibly poor sharpening practices it really doesn't matter what method is used to get the edge sharp. As far as we have seen, any difference between blades sharpened with different methods/equipment is negligible at best. Other than the choice between polished/toothy, a ground 150 edge is a 150 edge regardless of the method used to create it.

For knives, we are really only concerned about a usable sharpness sharpness range of, say, 600 maximum or preferably less. We have seen from Mr. Mike's SET testing that within that range, a RHC 56 blade performs similarly to a RHC 60 edge. Both roll about the same with the same amount of use, and both end up about equally dull.

It seems to me the great equalizer is the relatively narrow apex width range of a useful edge. It really doesn't matter if the sharpener approaches the edge armed with ancient Chinese wisdom, specially imported, super expensive custom hemp wheels, or recites secret incantations whilst sprinkling magic Zen dust, once an edge is that thin it's gunna roll and get dull.

That is a good thing I guess. Imagine how dull life would be without a chance to do some sharpening every so often!

[Mark Reich]

I completely agree Mr. Bud.  IMHO, for all intents and practical real-world purposes unless the edge is grossly overhead by incredibly poor sharpening practices it really doesn't matter what method is used to get the edge sharp. 

Everyone should understand this, but there's a Chicken Little in every crowd. 

The most fundamental lessons regarding grinding vs heat materialize immediately. You have a chunk of steel, you put it against a belt, and you hold it there. Soon it becomes warm... then it becomes uncomfortably warm. 

OMG. What now?!! 

Many will spot the omnipresent bucket of water right beside the grinder, and toss the blade at it. Lesson 1... check.

You may think that heat generated by grinding would require a PhD in quantum thermodynamics to solve. Nope. Start grinding the bevels on one blade and you will automatically be dunking the knife before it gets too warm. It's either that or you let go of the blade and wait until it cools enough to pick it up off the floor.

All the cool kids will be dunking their blades and laughing at you. 

It can't take long to fully appreciate that uncomfortable comes shortly after warm. Hot comes later. Seeing color is a different realm of hot, and falls under Grepper's applicable term- "grossly overheated by incredibly poor sharpening practices". 

[Mark Reich]

In order to gain understanding of the meat processing plant's sharpening system, and see what I could determine about deburring and honing on high speed buffers, I tried to replicate their procedure to see what it might take to heat the edge enough to soften it.

I started with a vintage Gerber Balance Plus boning knife, which is a little harder than regular German kitchen knives, and probably very close to the best knife steel used in the meat processing industry. I re-profiled the bevel to about 10 dps with a 120 grit belt, then refined the edge with a used 400 grit belt. I viewed the entire edge at 60x, and everything looked great, including the rather large burr sitting straight up off the edge.

I don't have hard felt wheels because I haven't heard of any other use besides sharpening, and I don't use buffers in my sharpening process for two reasons. First, it's too much refinement. Second is lack of clear angle control on a wheel, which has previously resulted in spotty results.

Don't get me wrong though, I have four 3/4 hp industrial buffers, and I use all 8 wheels on every knife, so I have plenty of experience on the machines. I have never needed to use water (dip bucket) to cool anything while buffing. The amount of pressure I use is only enough to get the job done without causing much heat. This has always worked plenty well enough for me, no matter what I'm buffing.

I use a hard sisal wheel with black compound regularly, so I gave that a whirl. I did not change anything about the way I normally use this wheel. In other words, I didn't apply any more or any less pressure than normal, and I didn't use more or less compound than normal. Everything was just standard routine.

It took me way more than 30 seconds to remove the burr. I'd make several passes then examine at 60x. Each time I looked, I was satisfied with the steady progress, but I was surprised with the tenacity of the burr. On the other hand, I wasn't developing much heat at all, so I did raise the pressure a bit, and that made a difference.

After two more series of passes the edge was remarkably clean, and the blade was notably warm to the touch, which I would estimate to be around 85°-90°F. The entire process had taken 4-5 minutes, more than half of which was spent inspecting the edge.

Please remember, this is something I totally dismissed many years ago. I did not expect the edge to be very sharp, so I was pretty surprised that it measured an amazingly consistent BESS 65-70! Maybe I've been overlooking something...

I wasn't through of course. I needed to finish the edge with white compound. My white compound wheel is a well manicured sewn cotton buff, so I figured I'd give it a shot rather than loading white compound on my sisal.

Trying to keep it real, I applied more pressure as I made 10 passes per side, thinking this would be closer to what the meat plant's sharpener might do. I didn't fool around at all, and this probably did take about 30 seconds. The blade got warmer from this single series of passes than from the sisal wheel, but was not close to uncomfortably warm. I was a little surprised, but a sewn cotton wheel probably can't equal the friction of a felt wheel.

I was pretty sure I had rounded the edge by now, but it sure was nice and shiny! Actually, the edge was popping arm hair very aggressively. I took it in for a measurement, and I'll be darned if it didn't now measure BESS 55! Holy cow. This was unexpected, but the 3 finger test revealed something else. The edge was fairly slick.

I couldn't just stop there. I took it back to the white wheel for another shot. I had a pretty good idea of heat generation, so I just wanted to see if I could get a little sharper.

That's why you should always quit while you're ahead.  

[KnifeGrinders]

I've sharpened two more identical SWIBO knives for live boning trial - these knives are of the same catalog ID our butcher uses for life.
Both knives are sharpened at 12 dps the same way using our wire-edge free technique, with only one difference:

The Knife-1 is deburred on a rock-hard slotted felt wheel run on the half-speed grinder at 1425 RPM


While the Knife-2 is deburred on the same slotted felt wheel run on Tormek at 90 RPM


For this test, I deburred the knives using a knife jig for angle accuracy, to rule out any discrepancies; the honing angle is controlled with our computer software.
Both knives score the same 55 BESS - by what have been discussed in this thread, for mainstream knives this is a strong indicator of a clean apex free of any wire edge.

I've asked our master butcher to compare the knife performance between #1 and #2, and to the similar SWIBO knives he sharpens himself on benchstones - he does not know which knife is what, and can tell them apart only by number of dots on the handle.
The outcome is to tell us whether deburring on the felt at high RPM degrades the edge retention.

BONING TRIAL


In this trial we had to talk to the butcher on the need to adjust his steeling to the edge angle he may be not accustomed to. In previous trials he noted that the steel was riding on the edge shoulders not hitting the edge – and in this trial he specially tilted the steel a little to make sure it reaches the edge.

Feedback:
The knife #1 did 3 steer carcasses and 2 hind quarters, and the knife #2 did 2 steer carcasses and 2 hind quarters. They could cut more, but that was the entire load for that day.
The knives began razor sharp, and kept the edge very well (with steeling), overall they performed every whit as good as knives sharpened by himself.
These two knives did differ in performance, but very slightly and he cannot tell any of them winning over the other: the knife #1 better recovered sharpness in response to steeling; while the knife #2 initial razor sharpness lasted longer, for the good first 20 minutes of cutting.

The knife #1 end sharpness score is 240 BESS, and the knife #2 is 215 BESS.

SET TESTING
We SET-tested the knives we gave to the boning trial.


For the purpose of this SET, we sharpened more knives in the similar manner, deburring them on the same slotted paper wheel run at 2850 RPM, 1425 RPM and on Tormek 90 RPM (using a reducer bushing to fit the Tormek shaft).
The SET testing shows that deburring on a slotted felt wheel at 1425 RPM worsens edge resilience to rolling by 5.5% and its effect is comparable to the slotted paper wheel at 2850 RPM; the slotted paper wheel at 1425 RPM causes no detectable adverse effect.

SET testing summary follows, and complete data can be viewed here Link to SET data >>



We've put together our findings about deburring on felt and paper wheels in this article on our website:
Effect of Felt and Paper Wheel on Edge Retention

CONCLUSIONS

FELT
Deburring on solid felt wheel at high RPM is not recommended.
Deburring on slotted felt wheel at 2850 RPM is not recommended.
Deburring on slotted felt wheel at 1425 RPM is conditionally acceptable, provided that the contact of the edge with the wheel is less than 1 second per pass, sides are alternated with each pass, and number of passes is limited to 2 in one go.

PAPER WHEEL
Deburring on solid paper wheel at high RPM is not recommended.
Deburring on slotted paper wheel at 2850 RPM is conditionally acceptable, provided that that the contact of the edge with the wheel is less than 1 second per pass, sides are alternated with each pass, and number of passes is limited to 2 in one go.
Deburring on slotted paper wheel at 1425 RPM is recommended.

These findings made me take the edge apex overheating very seriously and replace felt/paper wheel grinders in our workshop with half-speed ones, switch to slotted wheels, and revise our deburring technique to minimise overheating.

Following these recommendations ensures the edge temper is not compromised in the process of deburring.
Though, by the feedback I am getting I can tell that the first response is typically that of negation.
The New Zealand scientists publish their articles, we spend weeks on studies and experiments and arrange for trials with the meat plant and butchers - nevertheless, having read all that people keep using belts and solid felt and paper wheels at high RPM in their sharpening; they are good for profiling and bevelling, but not for honing.

[SHARPCO]

Excellent work.

The paper wheel(slotted) running 3450 RPM is dangerous for especially thin blade. It's why I changed my buffer to 1750 RPM. However, care is needed as the 10-inch paper wheel moving at 4581 SFM.

[Ken S]

One of my still in process experiments is using an eight inch hard felt wheel with my T4. If I was starting over again, I would use a rock hard ten inch felt wheel on my T7. (In both cases, the felt wheel is used in place of the grinding wheel, not over the leather honing wheel. This gives a SFM of 235, not turbo charged, however, with little danger of overheating.

Ken

[KnifeGrinders]

A few quotes by Cliff Stamp talking on the overheating on the Spyderco forum.

"This is a common misconception, that if the edge itself (the full bevel) does not discolour then you are fine. But again we are talking about the actual cutting edge which is less than half a thousandth of a mm wide. This will over heat immediately on power abrasives."

"It is a common misconception that as long as you hold the blade with your hands, and cool it frequently you can avoid over heating the edge - this is false. The very edge is extremely thin, less than half a micron, it overheats instantly on a belt sander or any other powered abrasive which runs at a high RPM...
The over heating is just on the edge itself, not the actual bevel as the bevel will heat sink into the main body of the blade."

"What is even worse is that the common "solution" is to water dip the edges and thus you are seeing steels which should never be water cooled being done so and thus you are going to get quench cracking...
As soon as it exceeds the tempering temperature it will start to soften the steel, this can be as low as 325 F. The second problem is that the constant subjection to over heating and quenching in water is very violent on the edge even if the steel is suited to those temperatures (high speed steel for example will not suffer temper drawn but will suffer quench cracking)..."

" This isn't an opinion or conjecture, this is materials data, which has been verified and published in the literature. However it also has to be noted that we are simply talking about optimal performance, it isn't like if you sharpen the knife on a belt sander it explodes when you cut a piece of cardboard, it simply doesn't have the same level of edge holding/stability/durability as when you sharpen by hand, ideally with a coolant (water stones)...
Of course you can just use water cooling systems (Tormek)."