Burrs - SEM imaging - thoughts & theories

[chiral.grolim]

What variables could be changed to create additional helpful observation?

edge leading vs edge trailing on waterstones would be what I love to see, both from side angles and directly down at the edge measuring apex width. Then repeat the same experiment on diamonds and see which ones are optimal for each type of stone.

:thumbup:

Also perhaps scrubbing/cleaning the diamond hone between each pass to ensure maximum penetration ("grab") of the abrasive particles.

 

[HeavyHanded]

edge leading vs edge trailing on waterstones would be what I love to see, both from side angles and directly down at the edge measuring apex width. Then repeat the same experiment on diamonds and see which ones are optimal for each type of stone.

Edge trailing on diamonds won't turn out so well I imagine. Whether it works well on the waterstones depends a lot on how hard the binder is in my experience. Tends to make a toothier edge with narrow cross section compared to a leading pass. I know varying the amount of mud makes a big difference, and I'd also imagine different suspension might have an effect. Cannot recall if Todd said he used oil on his DMTs, but a few drops of mineral oil might be interesting. Also might be a difference between the moncrystaline DMTs and a polycrystaline used by Smith for example, at the same grit value.

The easiest would be to put the rig on a postal scale or other accurate digita scale and see if a few ozs up and down makes a huge difference with the current methods.

 

[eKretz]

Try drawing a diagram to help visualize what I am suggesting. Even better, simulate the effect with a lump of clay; please take pictures and report back.



The spine is in contact with the hone and I don't think it can unintentionally lift enough to explain this bevel profile.

I can already visualize it. Deflection would cause less material to be removed at the apex and more to be removed a ways behind the apex - making the apex more acute, not more obtuse. This is why I said it would make more sense to me if instead the apex were being pulled down into the stone harder by the force of the edge-leading cut; when it springs back to center -there would have been more material removed at the apex than if it had remained in its relaxed state position - and you have your more obtuse apex. If I somehow have it wrong, I'm not sure how, please enlighten me.

 

[ToddS]

I can already visualize it. Deflection would cause less material to be removed at the apex and more to be removed a ways behind the apex - making the apex more acute, not more obtuse. This is why I said it would make more sense to me if instead the apex were being pulled down into the stone harder by the force of the edge-leading cut; when it springs back to center -there would have been more material removed at the apex than if it had remained in its relaxed state position - and you have your more obtuse apex. If I somehow have it wrong, I'm not sure how, please enlighten me.

I see the source of confusion - when I say the apex is flexible, i mean plastic, not elastic - the apex does not spring back into position. When the apex is bent away from the stone, metal will project above the plane of the bevel on the other side. That displaced metal is then removed when that side is honed.

The net effect is a nearly perfect edge - it not "toothy" in any sense of the word. (It does have some micro-convexity, which may be consider imperfect). Essentially the apex has been "moved back" from the projected bevel surfaces to the depth of the scratches. In other words, the scratches do not reach the apex.

I do appreciate you pointing out where I have not been sufficiently clear; this is discussion is very helpful to me. Let me share something with you that will either crystallize what I am saying or simply blow your mind: Try shaving from a razor FINISHED on a DMT coarse (325) - completely remove any existing structure with 100 light laps. Strop normally on clean leather before shaving. If you are hesitant, look carefully at the images I have shared.

 

[eKretz]

No, I understand what you're saying now. You're saying that the deflection exceeds the yield strength of the steel for the thin section at some point behind the apex and results in the steel being permanently bent up and away when the hone side is being stroked on the stone - and then some of the excess sticking out past the plane of the bevel gets removed at the very apex when the blade is flipped, before again being displaced and taking a set on the reverse side. Now I understand your theory very clearly. I was under the impression that the edge would spring back to center being hardened steel and having a fairly high yield strength - but at times I forget about the very small scale we're working with here - it wouldn't take much at all to yield the steel at that thin a section width.

This also "crystallizes" another conundrum I have been discussing on another forum about diamond plates and the seeming scratchiness on the bevels vs. the fairly uniform and considerably less scratchy resulting edges. It would seem that you are saying this is the result of the apex movement letting only the very tips of the diamonds do their work on a very shallow level, something like when a strop is used with a diamond grit on a flexible substrate. Is this correct?

Thanks for the clarification, much appreciated and after reading the first paragraph I had lit upon the misunderstanding. Keep up the good work!

 

[ToddS]

...
This also "crystallizes" another conundrum I have been discussing on another forum about diamond plates and the seeming scratchiness on the bevels vs. the fairly uniform and considerably less scratchy resulting edges. It would seem that you are saying this is the result of the apex movement letting only the very tips of the diamonds do their work on a very shallow level.....

The "grit" of consequence here is not that of the individual diamonds, but rather the "effective grit" of the contacting surface of those diamonds. The diamonds on my D10C are polished to a level where they produce a keener edge than a Gokumyo 20k. At the same time, abrasion is fairly slow, some might say my plate is "glazed" and no longer effective as a coarse grit hone.

 

[eKretz]

Right, that is the same thing I tell people all the time. So in effect, the combination of those two things, the "effective" grit being finer due to diamond wear and the apex flexing away combine to allow a much finer edge to be produced. My next question: does all this flexing back and forth due to the duller diamonds cause weakness in the edge due to fatigue?

 

[ToddS]

... My next question: does all this flexing back and forth due to the duller diamonds cause weakness in the edge due to fatigue?

You can answer this question yourself after a few shaves with the DMT325-finished razor...

 

[eKretz]

Sounds like a yes to me, lol. I will give that worn DMT shave a try tomorrow.

And BTW I just reread page 2 and saw your explanation for the convexity that I must have missed previously. Feel a bit dumb now, sorry! Don't know how I missed that.

 

[slamosam]

Todd, thanks very much for putting together your blog back by amazing SEM images :thumbup:

I try to figure & think about what being said about subtle apex convexity. What is your straight razor steel type+hrc & h1 hrc? I am asking because many steels at high hardness (58+rc) low or high toughness, once bent (exceeded tensile or plainly exceeded their elasticity) steel would be weaken and would easily deflect/bend away from honing side. I agree, with a broken-in diamond plate, you can get very refine edge but as for reasons - yours sound good but I am wondering...

For burr formation, I think (Young modulus) bend w/i elasticity radius outter surface (stretch part) got cut-off by edge-lead abrasives. Hence instead of spring back, the bend is permanent (envision a bend stick and the outter part get cut == snap). The compressed inner surface stay compressed until hone switch side, now it's complete/true/100% burr/wire.

 

[ToddS]

These particular images are from a vintage Genco razor. I don't have hardness numbers for it, but it is above average for a straight razor.

 

[eKretz]

Todd, finished my shave off of a worn Atoma 400 this afternoon. One pass WTG and one pass ATG. Not bad! Got a few painless weepers, and maybe not quite as close ATG as a real finisher, but not bad at all! Alum rub afterward resulted in maybe a 1 out of 10 on the owwie scale. Quite surprised me, even though the edge shots in your images and my own looked passably good (my scope is only good for ~150x though).

 

[ToddS]

I can't get much of an edge from my Atoma 400, but then I only use it for lapping waterstones. Certainly the DMT 325 "feels" much smoother when honing on it.
Your next challenge is to convince at least two people on "the other forum" to try this.

 

[eKretz]

Yeah my Atoma 400 is seriously whipped. It has been used mostly for lapping also but I really smoked it on quite a few very hard stones. I do a bit of "rockhounding" and flattening and raising slurry on super-hard "found" stones really takes a toll. I'd bet the DMT would give a better finish actually since it doesn't have the interrupted surface. I have one but my Atoma is the more worn of the two so I figured I'd try it. I'll see what I can do about getting a few others to give it a go over there.

 

[ToddS]

Unfortunately, the result may not be repeatable. After the SEM of the test razor, I honed another razor for shaving and it performed spectacularly. But when I tried re-honing the same razor on the same DMT 325 I had difficult time getting any keenness at all.

 

[eKretz]

Perhaps that had to do with the fatigued steel near the edge. Maybe that's something people who use diamond plates should be watching out for? Not to use too badly worn ones if they want the strongest possible edge.

 

[ToddS]

Maybe this image gives some idea of what can happen with the coarse diamond plates. There are really two grits at work; that of the individual diamonds and that of the surface of those diamonds. The surface of the diamonds refines the edge to shaving-keen; however, the individual diamonds lead to coarse chips. In the image below, two such chips are shown with a 25 micron circle (expected size for this DMT 600 plate). Again, this is just for illustrative purposes. I am not drawing any general conclusions from these few images.

 

[eKretz]

Todd, here are a couple edge shots from my DMT 325 edge I honed up tonight. On the first attempt I got a similar failure to the one you described - only capable of HHT1. On my second, after 100 more very light laps, voila - HHT3/HHT4.

Attempt 1:

Attempt 2:

 

[ToddS]

You can see that the scratches do not reach the edge - the usual indication of a micro-convex apex.

 

[REK Knives]

.

I do appreciate you pointing out where I have not been sufficiently clear; this is discussion is very helpful to me. Let me share something with you that will either crystallize what I am saying or simply blow your mind: Try shaving from a razor FINISHED on a DMT coarse (325) - completely remove any existing structure with 100 light laps. Strop normally on clean leather before shaving. If you are hesitant, look carefully at the images I have shared.

I'm not as daring as others... I would have to see a lot of microscopic evidence before I attempted this! That would seem to produce a very rough shave lol

I have seen evidence elsewhere where the lower you go in angle (on an edge) the more effect the grit has on leaving a ragged edge. So an edge finished at 11 dps on a 325 grit diamond plate would be a ragged edge indeed. There is a reason people have been shaving off of high grit stones for years....