Thread: Verhoeven Paper Question

He didn't post the edge dimension. But if the strop couldn't even straighten out the burrs it's unlikely to have drawn out the thicker bevel.

I couldn't help but giggle when I read that a plain leather strop couldn't remove a burr.

This will come as a big (and humorous) surprise to hundreds of woodcarvers and knife sharpeners who do it every day. I have personally done it dozens, or hundreds, of times with woodworking tools and knives. It is faster on a pasted strop, but still works on a plain one. If Verhoeven couldn't do it then he needs a better technique, a much smaller burr, or maybe some different leather. This is a neat example of an instance where a scientific study is directly at odds with the practical experience of many craftsmen.

The stropping-on-plain-leather experiment was done in two different parts of the test (honing and tormek) in two different conditions (lab and a workshop) by two different people (Verhoeven and Pendry), and had the same results. Verhoeven also tested both hard and soft leather and saw no real difference.

These two leather tests were repeated with chrome oxide pasting and they observed the sorts of improvements that we ourselves see. So I'm at a loss as to what they could have been doing wrong on the plain-leather test that they did right on the pasted leather test, and am inclined to believe that leather just isn't abrasive, and all it really does is shove the edge back into alignment.

Now he did use a hard backing for his leather strops, so the lack of sag may have made a difference since there would have been less pressure on the edge. But thats how the woodworkers strop their chisels, and they claim their bench strops do make a difference. It may be that they use more pressure than Verhoeven did.

I've never really seen the leather act like an abrasive - it can improve an edge a bit after it comes off the hone or linen, but you hit its limit really fast, within 30 laps or so. I've tried doing hundreds of laps on the leather to see if it will improve further and haven't seen it. But the linen side does seem to behave more like you'd expect a hone to act - you can keep stropping a dullish razor and it will keep getting sharper, and as you go on and use less pressure you get more sharpness. My one serious test of this involved trying to sharpen a dull razor using only the linen. It took around a 1500 laps* but the blade improved over the course of this stropping session until it finally came back to shave-readiness.

*I don't think it really should have taken that many laps, but I made a mistake. I started on a new Illinois strop with that plasticky linen, and it seemed to get the razor decently sharp within about 400 laps, but the edge was still rough, so I kept going and at the 800 lap point it was still rough so I kept going and when it was unchanged at the 1200 lap mark I switched to my Craftsman strop, and that got it smooth and sharp in a few hundred more laps. I suspect that 3-400 laps on the Craftsman would have done the trick. I know that sounds like a lot, but it's maybe 10 minutes worth of work. Also, after the 800 lap mark I did 500 laps on plain leather to see if that would smooth out the edge and didn't see any real improvement. So the razor really had about 2000 laps on it in the course of the evening: 800 Illinois linen (sharp but rough), then 500 Illinois leather (did nothing), then 400 Illinois linen (did nothing), 200 Craftsman linen (sharp and smooth), 100 Craftsman leather (sharper and smoother). And yes my arm was really really tired by the end of it.

I can and do regularly remove small burrs (on German and Swiss chipcarving tools, mostly) all the time. This is sometimes done using plain leather on a flat surface. Here's a reference by just one expert on woodcarving: How to Carve Wood: A Book of ... - Google Book Search. Oddly, I have one of the very first editions on my own bookshelf. It originally came out in 1984. I just did a quick google search on "can stropping remove a burr" and found it near the top of the list.

I have come to believe that plain leather demonstrates abrasive qualities every time I use it.

A few weeks ago, I re-read the Verhoven paper carefully. I noticed something on re-reading that might explain the non-existent stropping results he got with plain leather.

On page 4 of the paper, in the lower right hand corner, he has a table showing the 2-Beta (business edge) of various implements. He lists the 2-Beta edge angle for razors is 15-19 degrees, kitchen knives 20 - 30 degrees, utility and chopping knives 30 - 60 degrees. The straight razor shown in Figure 8 on page 7 measures 17 degrees, smack dab in the middle between 15 and 19 degrees.

But yet - on the machine sharpening with the Tru Hone machine described on page 8, hand sharpening on page 18, and Tormek machine sharpening described on page 25, the 2-Beta blade angle in all tests was between 40 and 49 degrees.

It seems to me that leather stropping only has an effect on the very finest edges. It also seems to me that leather stropping would have a much more noticeable effect on a feathery 17-degree edge than it could ever have on a rugged 40 to 49 degree edge. Could it be this study under-represents razors as an anomaly, in order to concentrate on knife-class edge angles? I mean, the name of the paper is Experiments In Knife Sharpening, after all.

Originally Posted by Sticky

I can and do regularly remove small burrs (on German and Swiss chipcarving tools, mostly) all the time. This is sometimes done using plain leather on a flat surface. Here's a reference by just one expert on woodcarving: How to Carve Wood: A Book of ... - Google Book Search. Oddly, I have one of the very first editions on my own bookshelf. It originally came out in 1984. I just did a quick google search on "can stropping remove a burr" and found it near the top of the list.

I have come to believe that plain leather demonstrates abrasive qualities every time I use it.

All sources I ever read, including your link, always advice to dress the leather with an abrasive compound.
But strictly spoken, everything on this planet has some abrasive qualities even a cucumber sliced lengthwise in half. Entire mountains are reshaped by mere rainfall. The big question is, have we the patience and time to wait for it?

Originally Posted by FatboySlim

Could it be this study under-represents razors as an anomaly, in order to concentrate on knife-class edge angles?

Verhoeven conducted the leather experiments on flat hones and flat leather strops, using this jig, leaving the specimen blades attached in the jig during the entire honing and stropping progression:

(picture taken from page 18 with reference to the original article at http://mse.iastate.edu/fileadmin/www...nifeShExps.pdf)
He checked his results at 3000X magnification, using an Scanning Electron Microscope, and found no discernible diminishing of 6000 grit abrasive grooves.
That is as scientifically bulletproof as it gets. Verhoeven had to change his mind about leather: "(...), it was initially thought that a clean strop would contain enough natural abrasive material to produce a marked improvement in the quality of the edge. As a result, several initial experiments were done with clean leather strops,including an experiment with alternate 3 cycles of 4 leather stropping plus a single 6000grit sharpening. In all cases the clean leather stropping proved ineffective in comparison with the dramatic improvement found with the chrome oxide loaded strop." (page 22 of same document)

For what it's worth, in my opinion, that closes the case. If stropping has an affect on an edge (and I agree it does), it clearly is not the result of any significant abrasion. The most likely explanation that remains, is proper alignment of the extremely narrow strip of erratic steel at the very tip of the edge. I advocate the use of the word "fin" for that strip. Stropping on clean leather is friction and it aligns and straightens out the fin of an edge. Stropping on paste is an entirely different thing.

Bart.

Interesting that there is so much variance in opinion on the results of stropping on leather. Apropos, in the barber manual excerpt on honing and stropping located here in the help files it says,"When the razor is freshly honed,it should be finished on the leather only. Subsequently, it is advisable to use the canvas first, then the leather,each time the razor is stropped".

So what do you gentlemen think of this admonition ? I can't resist going to the canvas having read of mparker's and others results with one or the other. I have tried going to the leather only immediately following the honing but I am not sure what difference it made in omitting the canvas. Seems to me that I do get more effect with the canvas first.

Personally I find that that the strop "cleans" up the edge after the my finish on a 12k. It just smooths the edge and refines the cutting properties.

I am finding with Mr. Ugly that I really do not use my dusted canvas. The draw on Mr. Ugly is so great that is seems to so two jobs in one.

Originally Posted by Bart

All sources I ever read, including your link, always advice to dress the leather with an abrasive compound.

How about neatsfootoil that Tony provides with his strops: AFAIK it does not contain an added abrasive.

Originally Posted by Kees

How about neatsfootoil that Tony provides with his strops: AFAIK it does not contain an added abrasive.

Hi, Kees,
I was talking about benchstrops for honing chisels and such, in response to Stickiy's post about sharpening tools for woodcarving. Most sources advocate dressing the strop with some kind of abrasive compound, often CrO or diamond paste. Neatsfoot oil is used for nourishing leather. I don't really see the connection.

Best regards,
Bart.