Thread: What Does it Mean, Taking an Edge too Far?

Originally Posted by unit

I'll pull this image if I have it wrong, but are the bottom two illustrations what you mean? As in the green material in the bottom is ground away and no longer supports the apex?

Where's the fin?

Originally Posted by gssixgun

Yes but that is over simplified

Yeah, well, all models tend to be over simplified for demonstration purposes...if you want to get really technical about it, my apex angle is well outside the acceptable range for straight razors in those images.

and c'mon, look at my handwriting...you are lucky there is not coffee stains and lunch on this drawing!

Originally Posted by gssixgun

(if you wanted to go really advanced we could discuss my thoughts about why some stones work better for some steels)

Actually, this is something I might enjoy discussing at some point. I have developed similar hunches with regard to steels and hones for knives...it seems reasonable to think there could be good and bad marriages between steels and hones...but you have to be a few standard deviations away from the average hone job

There might be a better venue for such a discussion, but if you ever start one, send me a link

Great pic which brings to mind, Not to hijack this thread, I would think that if this edge was not polished that it would make the shave harsh or would this shave angle be to shallow. Lowest exp if the hone in the pic what the surface of your skin.

Glen I read your blog a little while ago. I'm new to hones but would like to hear your thoughts on the diffs between the w&b and Friodur's and why?
Alex

Originally Posted by DaveW

(i still would like to see actual SEM pictures of the *edge* of the razor, and not the bevel - before and after stropping. Are there any of those?)

Verhoven http://www.google.com/url?sa=t&rct=j...dOblj9NWadTmUw
has SEM photos of .5 micron edges.

You will be disappointed. He didn't observe the effects of stropping. Glen did some stropping tests a while back indicating that overworking the edge at higher grits (as in pasted strops) wasn't a practical consideration.

I have intentionally worked edges with a barber hone til it was apparent at 45x the edge had broken down. It was "overworked". The edges went from straight and even and sturdy enough to cut without apparent damage to feathered and burred which would break while cutting and result in course torn steel.

IMHO those times we have a edge which seems harsh the culprit is very tiny "teeth" from the scratches which sub-microscopically run all the way to the edge and protrude. Our face can feel them but they are too small for even the SEM to view. Burnishing(or actually pressure flowing them) by stropping smoothes those tiny points back to the straight of the edge. At such a granularity which must be significantly sub .5 microns the steel actually is formed by pressure and heat from the leather. At this small scale steel isn't behaving like we observe it to at 45x. Your own skin burnishes the razor. Leather is tougher and doesn't complain.

Recently someone was testing a honing job I did. One comment was "harsh" so they stropped the blade. Further stropping beyond what I had done took the razor from sharp but harsh to simply smooth. Often users comment about Feather blades being too sharp or harsh until they are shaved a couple of times........burnished from use. Here is where YMMV or personal preference comes into play. Someone with finer sensory ability (denser nerve endings?) would feel the "teeth" more acutely.

Finally consider what has been published about DE blades. They are honed to 1K or less and then subjected to machine burnishing and coatings.

The situation of a razor losing sharpness part way through a shave might be nothing more than a underdeveloped honed edge which is cutting by virtue of some "teeth" which are extending past the edge which hasn't yet been properly developed by getting both planes to meet evenly. The shave-ability of such an edge quickly disappears as those teeth are burnished back to the edge which hasn't yet been properly formed .

All this indicates to me the knife sharp term of "wire edge" or burred edge(the often recommended treatment is drawing the blade through some material to tear off the burr) isn't a term which accurately describes what happens when we get above 4k-8k grit level.

I don't believe at .5 microns and below there is any steel which is going to survive much flexing back and forth against skin or leather. It would seem to me stropping works because at these sub-visual levels the steel is being formed into a smoother boundary which slides more easily across the nerve fibers on our face whereas the unstropped edge has the capacity to rake across these nerves and cause discomfort. Both of these conditions result in sharpness which for a knife would be superior but when applied to the sensitive skin on your throat are very different indeed.

Originally Posted by gssixgun

(if you wanted to go really advanced we could discuss my thoughts about why some stones work better for some steels)

Go for it. I've not seen a lot of information about the alloys used on the first razors that got away from plainer carbon steels. We know a lot about the diemaking steels now (A2, O1, D2, and W1..what's left of it) in terms of what their carbides are, and what cuts them the best.

I haven't seen a lot about alloys from pre WWII, though, and how precisely they were hardened and tempered to avoid carbides (what they look like microscopically, etc). Regardless, anything with modern al-ox, ceramics alumina, silcon carbide, diamonds, chromium oxide - cuts them all, hard carbides or not.

Lee valley has just released a powder metal that sharpens about like A2, has about twice the wear resistance in wood, but seems to hold acute angles better even than carbon steel. It's not a high speed steel, and they won't divulge secrets, but if it holds acute angles and has no large particles, it would be fantastic for razors. It seems to do well in both chisels and plane irons, which pretty much covers damage due to impact (which hairs do) and adhesive wear (which strops do, and hairs probably do, too). If it has that kind of wear and impact resistance, but still can be sharpened on natural stones, it would straight up be better than anything out there right now that razor makers are carrying over from bearing steel, knife making steel or diemaking steels.

Originally Posted by jaswarb

SNIP

All this indicates to me the knife sharp term of "wire edge" or burred edge(the often recommended treatment is drawing the blade through some material to tear off the burr) isn't a term which accurately describes what happens when we get above 4k-8k grit level.

SNIP

I enjoyed your post (even the parts I removed in the quote above).

I have surmised that (at least with some of the high carbide particle metallurgy steels in the knife world) that there is a point where the steel stops behaving as a homogeneous entity and starts to really show its heterogeneity (based on the scale of abrasives used). I lack the ability to test this, but I thought I would share the hypothesis.

Some steels seem to really be happy with coarse finished edges, while others seem to keep getting better as the grits get higher (to a point perhaps)...at least this is what I have observed in practice/trials.

Originally Posted by unit

I have surmised that (at least with some of the high carbide particle metallurgy steels in the knife world) that there is a point where the steel stops behaving as a homogeneous entity and starts to show its heterogeneity (based on the scale of abrasives used).

I concur. I believe one significant reason the powdered steels are advancing the art is they are more homogeneous and Hitachi's White steel can be taken to an incredibly fine hard edge which doesn't normally appear to have grain.

Originally Posted by kalanyon

Great pic which brings to mind, Not to hijack this thread, I would think that if this edge was not polished that it would make the shave harsh or would this shave angle be to shallow. Lowest exp if the hone in the pic what the surface of your skin.

I would surmise that "it depends" (and admittedly this drawing is pretty simplified)...but for the sake of simplicity, lets play...

If the honing continued until the bevels were polished all the way to the edge (or apex), the result would be a very sharp edge that is VERY delicate because the effective edge bevel angle would be much lower...giving the result of minimal support behind the apex.

If the honing stopped as shown in the bottom drawing and only the green material was removed, the resulting edge would not be polished (at least not by the honing efforts depicted in the drawing), it would not be made any sharper by the efforts depicted, and it would be weakened, but not to the extent of the example in the paragraph above.

The result in reality would probably be more like a convex shaped bevel (as a result of honing pressures being varied all over the place by inconsistent honing technique) with an effective apex angle on par with the geometry of the razor (therefore sharp) but ample shoulder material removed causing weakening.

This whole discussion sort of illustrates the importance of magnification in conjunction with a thorough shave test....at least to this novice

Originally Posted by hoglahoo

Where's the fin?

I dunno, all I see are two bicycle seats and a Phillips screwdriver head.

Originally Posted by jaswarb

I concur. I believe one significant reason the powdered steels are advancing the art is they are more homogeneous and Hitachi's White steel can be taken to an incredibly fine hard edge which doesn't normally appear to have grain.

White #1 and White #2 are excellent, even Blue #1 and #2 would be great.

Pre 1900 razors, what were they made of? On the list of carbon steels, they were one notch above file steel as the best grade of steel. But did they have vanadium carbides? Or were they an attempt at the best crucible process steel?