Verhoeven Experiments on Knife Sharpening--Wow!

Jeff Clark

Jeff Clark

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Apr 27, 1999
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This may be the last word on knife sharpening. There are pictures of things here that I have only visualized in my mind. Things that I have wished that I could see and illustrate. This pdf is nearly 8 meg long. I can probably stop talking about sharpening now. I am truly humbled:

http://mse.iastate.edu/files/verhoeven/KnifeShExps.pdf

Verhoeven is The Man! :eek:

Download this and save it. The way things go it may not last on the net.

PS you should also see his other works on blade metalurgy and craft. They are equivalent in size and depth.
 
Very nice! Truely the last word on sharpening. Thanks for posting Jeff. If I recall correctly, Verhoeven was the guy who collaborated initially with Leonard Lee?

I think I am going to try the Razor sharp honeing guides!
 
HoB,

I have a Razor Edge 'Cub' guide if you want to borrow it. It's for blades less than 4" long.

Jeff,

Thanks for the link! Will it answer the question I bugged you about recently?
 
For those who don't get to read my email Thom's recent question was:

"Many of your bragging edges seem to involve a belt-sander then some love with various waterstones before finessing the edge with the Sharpmaker. Does smoothing out the relief grind in such a manner provide better perfomance for the edge you set with the Sharpmaker?"

I don't know if the document I linked to would answer this question since I haven't read it all yet.

If I had a real nice pat answer I would have responded to his question via email yesterday. Since it involves thinking I delayed my responce.
(a) I don't know for sure.
(b) There are several types of "performance" and I hope that I am improving at least one of them.

What I typically do is sharpen my blades to as low an angle as I have time or nerve for using sanding belts down to 600 grit. I don't have anything finer or I'd probably keep going with the belts finer yet. After the 600 grit I usually switch to a 1000 grit waterstone. I use it to put a finer polish on the bevel I just made, remove burrs, and also to remove material that was possibly weakened by the power sander. I like sanders for speed, but I worry that the high forces and rapid ripping apart of metal bonds caused by the fast moving belt may leave weak spots in the edge. Some weak spots would be from material sort of hammered out of its original place by grit on the moving belt impacting it. Other weak spots might be wisps of edge material that were touching material that got ripped apart rapidly by the belt and hence the wisps got overheated and had their heat treatment compromised. By using a waterstone (or sometimes an ultrafine diamond hone) I remove enough material that I hope to get down to a solid edge substrate. These types of hones leave a smooth finish yet cut pretty fast.

I hope that the smooth finish will also help to provide a solid foundation for the edge. I figure that rough spots can lead to stress concentration or uneven edge support that would promote localized edge rollling. I would like the finish to be as close as possible to the final finish that I'm going to apply using my Sharpmaker, but I don't want to waste a lot of time on material that is a step back from the edge. I hope that the smooth finish will provide lower drag than a rough edge. I am pretty sure that is true. For a bragging edge I hone at around 10 degrees per side on Sharpmaker rods, working down to the ultra-fine rods that don't come standard with the kit.

My current bragging edge has another step after honing the ultra-fine rods, I strop on photographic paper or view-graph sheets coated with sub-micron diamond paste. I use .5 and .25 micron grit or 1.0, .5, and .25 micron. This lets me get an edge for toilet paper cutting tests.
 
That was an interesting read, the pictures were amazing. I read it on the plane ride to NYC right after New Years, and no nobody gave me a weird look. ;)
 
Jeff Clark said:
I like sanders for speed, but I worry that the high forces and rapid ripping apart of metal bonds caused by the fast moving belt may leave weak spots in the edge.
Click to expand...

So was I, I checked running cutting ability and edge retention trials with a D2 blade at 62 HRC with a 100 grit AO belt and it was identical if ran with full speed on a belt sander or by hand with the same abrasive.

It may depend on the heat resistance of the steel and other characteristics. I was also examining really coarse finishes, it may be different for fine polishes.

The PDF file on steels has a lot of interesting information, the section on heat treatment of stainless alloys is in particular infomative and has a lot of information I have not seen elsewhere.

-Cliff
 
If this is the guy that wrote the pdf on forging and heat treating from rec.knives, he's the man. That one book gave me the inspiration to try a whole bunch of new stuff after making my first usable blade from O1. Some unusable blades came before. Anyway, good stuff, even if its from a different guy.
 
I'm only about half-way through this, but it is very interesting. Just starting to use a leather strop as part of my sharpening routine, I found his conclusion that using a clean leather strop produced little to no results compared to one loaded with chromium oxide.
 
I first read this some time back and one of the things that really struck me was the water stone comparisons. Both by hand and on the Tormek. The Tormek dealers will tell you that a 4000 grit water stone is not worth the extra cost. This confirmed my own suspicions on the quality of this edge and I do use the water stone alot.

His writing on the need for a compound on the strop again re-enforced my own opinions on this. (Always glad to see my thoughts in agreement) I was surprised by the amount of stropping he found was needed, 12 plus passes per side on the Tormek. This would equate to ???? lets say a LOT of passes down a 8" strop. (30 seconds on a Tormek honing wheel which gives about 3 passes covers about 847 running inches if I did the math right) Since I read this I now strop by hand a great deal longer than I used to.

The one area I can't duplicate is his stropping/buffing with the Tormek. For reasons unknown to me I run into problems doing this. I'm either hitting the side of the Tormek unit or I run out of room on the guide bar. I still haven't gotten around to trying my stand off brace for this.

Freehand stropping on the Tormek just doesn't do it for me. Again blade length and running into the side of the unit. My results are way too inconsistent. Often I ruin a good edge while trying to make it better. I can't consistently strop/hone/polish acceptably with the Tormek. I'm doing something wrong. But I'll be damned if I know what. If anyone has any suggestions for stropping/polishing with the Tormek I'd be glad to hear them.

Now that I have the boron carbide I'd be greatly interested in seeing how the Tormek honing wheel handles this with HARD blades, if I can get good enough consistent results to measure the difference.
 
Thank you Thom, but I think I can afford to simply get the kit of both guides and see how I like it. They are not that expensive. Since I am a student on a limited budget I very much appreciate you offer though!
 
After reading Verhoevens article twice, I must say I can not agree with his reasoning of his conclusion (just a minor point of course).

He states that trailing strokes on waterstone produces larger burr formation presumably because debris is carried to the edge. On the other hand, CrO loaded leather clearly removes significant amounts of material, yet does NOT produce a significant burr formation, even though the stoke (or wheel direction) is always trailing. So it is clearly not the debris that is being carried. Also, at least in my eyes, even the trailing strokes on the 6000 waterstone leave a much better finish than any of the other abrasive media (excluding the leather loaded CrO).

I also start to wonder which edge is perceived to cut better. If you compare the finish of the 6000 grit and the 1200 diamond grit, you almost wonder how such a crappy finish as left by the diamond hone could possibly be cutting, yet many people seem to be very satified with it. That makes me wonder wether the slightly uneven finish left by the trailing stroke just produces an edge that feels just sufficiently more agressive.

Also, looking at the edge on images, I am not sure that I wouldn't give the trailing strokes the nod. Also even though there is a large section with a burr visible in the trailing-strokes image the rest of the edge seems to have less of a burr that the images for the leading-edge shows, which seem to have many little sections with a deformed edge. However, I wonder if the edge formation is really due to burr (on the leading-edge) or to impact on the abrasive particles, because they are mostly visible on down side as opposed to the trailing edge burr which appears on the up side.

Well one way or another. I am not sure if I am willing to give up my trailing edge stroke yet, but I will start playing with the leading edge stroke again.
 
I do a combo of forward and backward on the finishing stages. Back initially then finish with a forward 3-5 strokes, the back strokes seem to clean up the edge, the forward ones make it really cut well. I don't have cool pics to back that up, but it works for me and I am sticking with it.
 
I'm in sympathy with some of HoB's reservations about Verhoeven's conclusions. Just because you can observe that something looks better, or you can measure something that seems like it should improve performance, doesn't mean that you know what really works best or what causes the effects you observe.

I don't buy his explanation for what causes burs to form. I think that most burs are just material that did not get cleanly cut off the edge by the abrasion process. We visualize abrasive grit scooping out blade material as cleanly as a lathe turns down a piece of brass, but it doesn't. At corners or edges of objects even sharp cutting tools bend some of the material that they are cutting (unless it is hard like glass where it tends to chip). Think of a hacksaw blade cutting through metal--you always get a bur on the bottom side of your cut. Some metal just doesn't get stressed enough for it to break free from its original connection. It just gets bent over. If it happens with sharp hacksaw teeth think how much more it happens when you are cutting with random cubes of aluminum oxide grit.

As you hone some of the material just flops back and forth from side to side. It has no support so most of the bur does not push back against the hone. Right at the apex of the edge there is pressure against the side of the base of the bur, but not as much as you would expect. The blade itself is thin right there and the blade bends to let more of the edge rest flat against the hone surface than you would expect. You remove material back a bit further than at the apex because the blade is stiffer there. The pressure maxima is a little bit back behind the bur. Rather than the bur getting automatically cut off, it instead tends to get longer. This problem gets worse with low honing angles.

What I have seen experienced barbers do is using very short stropping and honing. Instead of running say 8 linear inches of honing/stropping per stroke they only make 2 inch strokes as they alternate side to side. They remove a minimum amount of material from one side before they switch to the other side.They are sort of whittling that bur down a little bit of a time from both sides.

As to what works best, I have a recent test case that surprised me. I buy Reynold's food service plastic wrap in 1000 foot rolls from Sam's Club. Rather than keep it in a box with a built in cutter I mount the wrap in a paper towl holder. To cut it I use a very sharp knife. Usually I use a knife that has been finished at a low angle using the fine rods of a Sharpmaker. I have recently been experimenting with stropping blades with submicron diamond abrasive. That improves shaving and several other measurements of sharpness. When I diamond stropped my plastic film knife its free hanging plastic film cutting ability went down. I repeated the experiment a couple of times. I refinished with the ceramic rod and plastic wrap cutting improved, I stropped it and the cutting deteriorated. I am sure that I have a finer edge after stropping on plastic film coated with 100,000 grit diamonds, but that edge doesn't work as well as the ceramic hone finish that is probably more like 4000 grit.
 
Its a great find Jeff. I too have read it twice now. I have some comments about the 600 grit edges. First off I have a 600 grit Edge Pro water stone that gives a very good slicing as well as push cutting edge. For my kitchen knives I prefer the 320 grit water stone. I'm sure under a microscope the edges finished with both these stones would look much as the photos in this great link but the truth is, "so what?" The edge is a 'micro serrated one" which explains readily why it cuts and cuts well for general utility. A highly polished edge with everything looking just pristine and perfect is not always needed except when you are needing to do some serious push cutting maybe. In actual performance I think some of the ones done with the 600 grit stone and a ceramic once or twice lightly would probably outperform the higher polished edges in real world tests. I can't prove that but its my gut feeling.

I generally have found the leather wheel to perform well myself. Now I know why I love it so much for my wood carving knives. Even still, I use my strop too and have also found that and the compound loaded on it to be the best way to remove a burr but I've said for years that I don't think there is any way possible to actually remove all of a burr formed on an edge. Its there even when we can no longer see it. How or why it is formed? I can't answer that. For all I know it has something to do with the motion. FWIW I have noticed that trailing strokes form a bigger burr but to me that was never a big deal because the final strokes on a ceramic rod and then stropping seemed to always remove it to my satisfaction no matter how it was initially formed.

Not trying to diminish all the technical info in anyway but in reality the only thing that really matters to most people is "does it cut or doesn't it?"

STR
 
When I read that file I said "So what?"
I hardly polish my knives smooth, in fact, I only keep one of my knives hair poppin' sharp. I sharpen my Spyderco Para on a DMT coarse diamond hone, then do 5-6 deburring strokes on the Sharpmaker medium rods. The knife never touches the fine rods or a strop (even though I own Sharpmaker fine and UF rods and a strop). The great toothy edge on my Para really cuts great, and is more durable of an edge than when I used to polish the hell out of it. I used to do the whole sharpen till it is a mirror, chase hairs off your arm sharp, but that is only useful for a knife you carry around and show off. I was extremely dissapointed when I tried to cut anything harder than paper. Now that I keep a practical coarse edge on it, it actually does aggressive cutting. I am going to try a DMT fine hone, but will probally no longer use my Ultra fine rods or strop anymore on my user knives.
 
Great find, Jeff, thanks for sharing the link!

I'm somewhat in a quandary about some of it also. I notice a great improvement with an unloaded leather strop on some of my edges, but he seems to think that isn't the case. Interesting.

If nothing else, this will get people thinking and discussing. That in itself is a good thing!
 
Dr. Verhoeven's study is excellent. It doesn't answer every question, but it certainly answers many and gives us fodder for other questions. Some of his findings mesh with some of ours; some don't; and some are truly new for at least some of us (well, maybe just me). There are so many ways to sharpen, strop, or load or position abrasives, let alone cut, that his study would never be able to cover everything. For Rusty Edge's cutting, a toothier edge will last longer. For woodcutting, various polished, convex edges work great. For wood carving, flat or barely convexed, polished edges do the trick. Verhoeven's study is kind of like the Rosetta Stone. It ain't the heiroglyphics; it just lets you understand them better.
 
The more I look at these wonderful images the more I am surprised how little the leather wheel with CrO burrs. It clearly removes some decent amount of material, yet is shows very little burr production, and that despite the fact that it runs away from the edge.
This essentially suggest, that you don't really have to be too worried about a burr in general, as long as you give the final edge a few passes on a leather strop or wheel to take of the burr.

Personally, I have adopted the methode of removing the burr by doing one or two very light passes at a greatly (5-10 deg) increased angle, on the stone that I am about to leave. I picked that up, either from you, Jeff (?), or was it Joe Talmadge, sorry I don't remember :o. Either of you were saying, that you were doing this, I tried it and it worked very well for me. I tried pulling the burr of, like Murray Carter does, but that didn't work as well for me.
 
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