Here is the beginning of a new study, that promises to be fun and informative, prompted mostly by Josh’s urging. Thanks Josh! In this study, we want to evaluate the effects of stropping at, above and below the sharpening angle, specifically the rounding of the edge that can be caused by stropping with a pliable material. I’ve cut some blades in cross section so that we can visualize the effects under the microscope, the image below shows what that looks like:
I’ll also evaluate the blades in the sharpness tester to see what kind of quantitative difference stropping at various angles might make.
The blade is prepared at 20 DPS and finished at 1000#. At each iteration, I’ll restore the bevels to 20 DPS with the 1000# stones before starting with a new stropping angle.
That’s a nice pointy tip you have there! Most people don’t focus on the tip long enough to get it perfect like that. That comes from years of experience for sure!
Ahhhh I see now! This is the “birds eye” angle - i.e. looking directly at the edge from the end of it (that’s why you sectioned it). Sweet!
Also, try to get pics on your 1600x from the side if you can (only if you have time, would be neat to see both angles). Man, I can definitely see the rounding with the strops! It is interesting that even with the stones it appears somewhat (lightly) rounded… is that your impression too?
It is interesting. For that reason, I want to clean up the sample a little more and start over to see if that’s really happening with the stones or if the edge is just that funky.
Slightly rounded or… Geez, that second photo looks like a classic micro-bevel. The angles seem too uniform to be accidental. What is the angle difference between the “micro-bevel” and the main bevel? Did maybe the sharpening angles get reset between the first photo and the second?
The rounding seen in the third photo is exactly what we’d expect, except that there doesn’t seem to be an appreciable rounding of the edge. Actually looks like a beautifully done convex job, but on a micro scale.
Just to elaborate a little on what I meant when I wrote “Haha. here we go again”. I was referring to the question what stropping actually does to a metal surface. Is it abrasion only or is there also something called “burnishing” going on, i.e. smearing metal around?
It is not what I’d expect. We don’t see rounding of the edge of the edge, which is what would happen if you’d strop at too high an angle. But what we see is a nicely convexed edge.
As far as I am concerned, the effects in observed in some of the microphotographs of stropping by Clay in the past cannot be explained by abrasion only. I have a hard time in explaining how the abrasion of a strop could suddenly turn the edge shown in the first photograph into a convex one. (It would require that the stropping force increases proportionally as the strop gets nearer to the edge of the edge.)
Leather strops, particularly with the WE pastes, are quite sticky. This causes quite a bit of stiction between the leather and the metal. (Definition of stiction: the force required to cause one body in contact with another to begin to move.) The has led some people to suggest that what we observe is also caused by burnishing that takes places due to this stiction. However others (particularly PhilipPasteur) have argued that there is no way in which leather can have such an effect.
When bodies are in sliding motion across each other and they are of similar hardness, there will be adhesive based wear which will include things such as fracture, welding, burnishing, etc. . If they are of very similar materials then this can be very high due to localized bonding. This is why you don’t want to use D2 to try to stamp 420J1 for example as there is too much chromium to chromium bonding and it produces high adhesive based wear.
A leather strop loaded with paste which is used on a knife will develop almost immediately metal particles on the surface, this when used again generates metal on metal contact and you get all the large mish-mash of non-abrasive interactions as you just have two pieces of the same metal grating against each other. Now it isn’t the only effect. This is complicated by the fact that you have at the same time the abrasion from the paste still happening as well.
The primary grind is somewhere around 11 degrees though you can’t see it in the photos. Then there is a 15 dps bevel that drops to a 20 dps bevel. Once the stropping was completed, the final edge bevel is around 24.175 dps.
[quote quote=“CliffStamp” post=19170]When bodies are in sliding motion across each other and they are of similar hardness, there will be adhesive based wear which will include things such as fracture, welding, burnishing, etc. . If they are of very similar materials then this can be very high due to localized bonding. This is why you don’t want to use D2 to try to stamp 420J1 for example as there is too much chromium to chromium bonding and it produces high adhesive based wear.
A leather strop loaded with paste which is used on a knife will develop almost immediately metal particles on the surface, this when used again generates metal on metal contact and you get all the large mish-mash of non-abrasive interactions as you just have two pieces of the same metal grating against each other. Now it isn’t the only effect. This is complicated by the fact that you have at the same time the abrasion from the paste still happening as well.[/quote]
Wow… I think you hit the nail on the head. From what I remember reading this theory has not been proposed as of yet and it makes a LOT of sense (more than any of the others I’ve seen).
[quote quote=“wickededge” post=19174]A note on the angles in the photos:
The primary grind is somewhere around 11 degrees though you can’t see it in the photos. Then there is a 15 dps bevel that drops to a 20 dps bevel. Once the stropping was completed, the final edge bevel is around 24.175 dps.[/quote]
How did the 15 dps bevel drop to 20 dps… was this on purpose? That is amazing that stropping at the same angle will actually raise your edge bevel around 4 dps!!! In effect what you are saying is that we need to lower the angle around 4 dps to barely touch the edge with the strops… although I am sure the amount of pressure you use plays a large role in this as well.
[quote quote=“razoredgeknives” post=19176]
How did the 15 dps bevel drop to 20 dps… was this on purpose? That is amazing that stropping at the same angle will actually raise your edge bevel around 4 dps!!! In effect what you are saying is that we need to lower the angle around 4 dps to barely touch the edge with the strops… although I am sure the amount of pressure you use plays a large role in this as well.[/quote]
I added the 20 dps micro-bevel because it gave me more room for lowering the angle later with different stropping angles, plus it’s easier to see the whole bevel in the scope.
I was using a lot of pressure, more than I normally do when stropping, to the purpose of trying to visualize the effect. As this study progresses, I’ll play with pressure some, maybe even mount the sharpener on a scale to see if I can quantify how much pressure I’m using with each stroke.
I reestablished the 20 dps angle and cleaned up the cross section a little more:
This second image is from the side at 2000x. The line you see at the edge is the reflection caused by the immersion oil. Everything to the left of that line should be ignored as an artifact.
You’re correct - they’re of the 1000 grit diamond plates. I wanted to reestablish the 20 dps bevel with the 1000 grit diamonds after I’d cleaned up the cross section. Now I’m off to strop it again and will post new pics as soon as I’ve got that done.
anxiously awaiting the results!
