My Theory on Razor Overhoning...

jendeindustries · Aug 1, 2011

Over on the Knife Forums, we had a friendly knife sharpening competition which included some serious sharpeners. Part of the competition called for documenting before and after pictures under magnification, and I saw some amazing things that drove home what I had been contemplating about the theory of Razor Overhoning - which I don't subscribe to.

Here is a link to the article, and I encourage discussion here.

Thanks!

life2short1971 · Aug 1, 2011

I read the article directly related to this link and those pics clearly show the need to get those deeper scratches out on razors that are subject to chipping. Thank you for posting this!

global_dev · Aug 1, 2011

very interesting, underhoning... hmm... time to back to the hones.

jendeindustries · Aug 1, 2011

Thanks, Gents!

I had noticed that no matter how long or how lightly my strokes were or how perfect the scratches were under the scope on the 2K and 3K stones, the 5K+ always revealed some deeper ones. I was thinking that each successive stone needed to first remove the peaks left by the previous - when those peaks get removed, the weakness of the valleys becomes apparent, and then chip out. That's why one must actually hone more so as to establish the new stone's peaks and valleys, or scratches. Each step must go through the same process.

Kentos · Aug 1, 2011

Great article! Even greater theories and pictures!

dakotaev · Aug 1, 2011

Great article. I have experienced these micro chips such as the pictures describe and your theory makes very good sense of it. Thanks Tom!

Balcmeg · Aug 1, 2011

Great article - even i could follow it!

Your thoughts make good sense to me and its a "simple" explanation - simple is always better than complex.

Gustav · Aug 2, 2011

Thank you for posting this article it made for a most interesting read and it makes a lot of sense too, at least to a newbie.

jimmyh · Aug 2, 2011

Huh... I assume you've seen that trend in a lot more pictures than just the ones shown?

The scratch marks seem polished out below the valleys already. It looks like it must be weakening the steel significantly deeper than the strach itself? Do you have any estimates of how thick that bevel is or how deep that scratch is?

Balcmeg · Aug 2, 2011

I am not sure if I can get this right in english, but as I see it the actual "hack" in the edge would become quite deeper the the actual scratch as a result of the rather steep angle. I

jimmyh said:
Huh... I assume you've seen that trend in a lot more pictures than just the ones shown?

The scratch marks seem polished out below the valleys already. It looks like it must be weakening the steel significantly deeper than the strach itself? Do you have any estimates of how thick that bevel is or how deep that scratch is?

jendeindustries · Aug 2, 2011

Thanks, guys. I usually do tend to make it overly complicated, and it can easily become so... :001_tongu

I do realize that there are many finer points to ponder and discuss.

Jimmy, great question - and the answer is yes. I have been seeing these things since day 1 of my razor honing journey with my usual scope, which has no picture taking abilities. Getting a razor to behave under the Veho without dinging or digging into the lens area is difficult, so I never really documented them.

There were multiple occurrences between the different knives, which really drove this home - especially since it was not a straight razor that this was happening on. The examples in the post were what I felt to be the most related to straights. You can find compilations of all the before and after pictures for the competition here. You should also be able to find links to the individual pictures here (easier than listing them all again as links here).

If you look again at the picture below you'll see another scratch to the left of the arrow on the left side of the picture (which is touching the head of the arrow). If you continue to draw those two lines toward the edge, you will see an intersection which is where the chip is. If you're old enough to remember the game Missile Command, that's where both lines intersect and overlap, and possibly made the metal too thin and/or weak, causing the chip.

As for the thickness of the edge, it passed the HHT right out of the box, so it was thin enough to shave with:

I can't fathom how deep the scratches are, but I do know practically everyone used a belt sander to thin the knife first, so it is my guess that this was caused way back in the initial stages, and the deepest of the scratches left by the belts were the results of the chips. FWIW, none of these chips registered on the edge tester test (to which I am very sensitive).

Bart · Aug 2, 2011

This pretty much concurs with what I always assumed to be going on with small chips that can be seen under magnification immediately after honing. They are just the deepest remnants of a saw tooth pattern left by the coarser stages of bevel formation.
"overhoning" by the definition of an edge disintegrating once it is supposedly taken beyond the keenness limit of a particular hone, is a hoax.
If the blade in the picture is honed further on the stone it was finished with, there will be no new chips to form. Quite the contrary: more metal will be removed and the bounderay that forms the very edge will slowly shift towards the bottom of the chips. The finishing hone may be too slow to "hone the chips out" within a reasonable time frame, but that is what eventually would happen. There is no single physical reason why a hone could abrade "through" the bevel. In fact, the hone only "abraded through" the steel at the very apex of the bevel. It leaves a particular type of edge jaggedness akin to that particular type of hone. The only reason why there could ever fall fragments out of the bevel, that are larger than a hone's normal abrasion, is when there is structural damage in the steel, caused by corrosion or stresses induced by erroneous tempering.

Kind regards,
Bart.

MajorBurnz · Aug 2, 2011

Bart - I agree with your summing up of this 'issue'. I also don't think there's such a thing as overhoning.

This brings up somthing that I adhere to pretty closely: start with the finest grit you can for any given razor.

If the razor needs a bevel set, I'll drop down to a minimum of 1500 grit. I've tried lower grits and always wound up with micro-chipping, which can take a while to get rid of. However, most razors come to me with a decent bevel. I'll check that the bevel is fine and then hone on my coticule or japanese natural with no coarser hone thrown in.

rajagra · Aug 2, 2011

Excellent observations. (I could be awkward and suggest the chipped-off metal caused the scratches, not the other way round, but I don't believe that's likely.)
The moral seems especially important for double bevels, but even with single-bevel razor honing the importance of doing each stage properly seems evident.

mkornecki · Aug 2, 2011

I'm not sure I really understand here... You claim that the coarser hones are causing damage below the metal surface which is then exposed by the finer hones? That seems to be a bit implausible. I also note that in addition to the scratches you circled, there are scratches all over the place. It would be hard to point to a piece of real estate on that edge that did not have a scratch that could be traced to it, in a line.

life2short1971 · Aug 2, 2011

They are not causing damage below the surface but they are leaving scores that become chips as the edge is stressed from shaving. If you notice every chip has a scratch from a courser stone leading to it and no chips where there is not a scratch leading directly to it.

Brownbear · Aug 2, 2011

Very interesting thread. I've seen the same thing on some of my edges and wondered... This certainly argues for patience in honing and using finer grits than maximum speed would suggest. I have noticed that after rehabilitating an Ebay wreck I sometimes can't get it sharp the first time I set the bevel and hone. So I take it back with a heavy slurry and redo it. I have assumed it is because of corrosion into the metal on the edge and the need to hone away rotten steel. I have had to repeat this three or more times on some edges before I can get the HHT to my minimums. But oddly, on these edges, once they hit the desired sharpness, the edge is often smoother than other blades that sharpened right up after coming off the coarser diamond plate. I had assumed this was all due to some inherent property of the steel and provenance of the blade, but now I am wondering if having to repeatedly go back to a thick slurry and correct the bevel wore away enough of the deep scratches from the initial bevel formation to reduce the frequency of these microchips. (I guess we have to stop calling them microchips, microgouges is more descripitive). I'll have to pay more attention next time, I guess it is time to get the scope back out and have a look see.

The low frequency of the deep scratches suggests that the coarser grit abrasives (sanding belts, diamond plates or whatever) have a small percentage of abrasive particles that are significantly above the mean size for the grade of the abrasive. Otherwise you would expect more of those deep scratches. I've been following the CBN threads with interest and Ken has shown some interesting size frequency diagrams that suggest that the CBN at least is pretty tightly controlled in its size distribution. I wonder if the standard deviation in sizes is correlated to the mean diameter. And I wonder if much of the difference guys see between synthetics and naturals is a function of the variance in particle size distributions. It wouldn't take a very high percentage of larger than average particles to put a few scratches along the length of a blade considering how many times the edge is rubbed on the abrasive. In fact if one particle was large enough to put a deep scratch in the surface and you did 100 strokes on that abrasive.............

This also argues for very good hygiene when honing, it wouldn't take much crossover from a previous larger grit to scratch the edge you are working up on a finer grit and defeat the purpose of the progression.

life2short1971 · Aug 2, 2011

Brownbear said:
Very interesting thread. I've seen the same thing on some of my edges and wondered... This certainly argues for patience in honing and using finer grits than maximum speed would suggest. I have noticed that after rehabilitating an Ebay wreck I sometimes can't get it sharp the first time I set the bevel and hone. So I take it back with a heavy slurry and redo it. I have assumed it is because of corrosion into the metal on the edge and the need to hone away rotten steel. I have had to repeat this three or more times on some edges before I can get the HHT to my minimums. But oddly, on these edges, once they hit the desired sharpness, the edge is often smoother than other blades that sharpened right up after coming off the coarser diamond plate. I had assumed this was all due to some inherent property of the steel and provenance of the blade, but now I am wondering if having to repeatedly go back to a thick slurry and correct the bevel wore away enough of the deep scratches from the initial bevel formation to reduce the frequency of these microchips. (I guess we have to stop calling them microchips, microgouges is more descripitive). I'll have to pay more attention next time, I guess it is time to get the scope back out and have a look see.

The low frequency of the deep scratches suggests that the coarser grit abrasives (sanding belts, diamond plates or whatever) have a small percentage of abrasive particles that are significantly above the mean size for the grade of the abrasive. Otherwise you would expect more of those deep scratches. I've been following the CBN threads with interest and Ken has shown some interesting size frequency diagrams that suggest that the CBN at least is pretty tightly controlled in its size distribution. I wonder if the standard deviation in sizes is correlated to the mean diameter. And I wonder if much of the difference guys see between synthetics and naturals is a function of the variance in particle size distributions. It wouldn't take a very high percentage of larger than average particles to put a few scratches along the length of a blade considering how many times the edge is rubbed on the abrasive. In fact if one particle was large enough to put a deep scratch in the surface and you did 100 strokes on that abrasive.............

This also argues for very good hygiene when honing, it wouldn't take much crossover from a previous larger grit to scratch the edge you are working up on a finer grit and defeat the purpose of the progression.

Very good points indeed.

honed · Aug 2, 2011

This awesome post pretty much sums up what I have had in my head re: the issue of over-honing
but I have never quite being able to express it.
It all makes perfect sense now.

Over-honing is dead. Long live under-honing!

jendeindustries · Aug 2, 2011

life2short1971 said:
They are not causing damage below the surface but they are leaving scores that become chips as the edge is stressed from shaving. If you notice every chip has a scratch from a courser stone leading to it and no chips where there is not a scratch leading directly to it.

Here is a transition picture from 2K to 5K - the 2K scratches are going to the top right, while the 5K are going to the top left. You can see just how much deeper those 2K scratches are at the edge.

You need to keep going until you get those deeper ones out, and end up with a fully established finer grit scratch pattern, like this finished 5K edge:

You'll see there are still variations in depth along the bevel -but there are no obvious 2K scratches left, and the edge of the edge is quite intact.

Here is the full progression I used for the pictures (it isn't a razor):
http://s765.photobucket.com/albums/xx298/jendeindustries/Microscope%20Pictures/?action=view&current=836165ce.pbw

Bart-

The finishing hone may be too slow to "hone the chips out" within a reasonable time frame, but that is what eventually would happen.

That is absolutely correct, sir! :001_smile

The only time I don't try to cancel the scratches out is on my 30K stones. It's just too darned slow at that point to deal with it.

Bear - Belts are notoriously fast, but also notoriously "dirty", as they are candidates for contamination from other belts, other materials lodged in the belts, etc., and on the high grits such as leather with .5 or smaller sprays an compounds, you even risk contamination from dust particles! Pressure from the belts (and from honing) also plays a huge role in the depth of scratches. As different stones abrade and polish differently, YMWV as to the overall consistency of the scratches.

Great stuff, Gents! Keep it coming! :001_tt1:

Search

My Theory on Razor Overhoning...

jendeindustries

life2short1971

global_dev

jendeindustries

Kentos

B&B's Dr. Doolittle.

dakotaev

Balcmeg

Gustav

jimmyh

Balcmeg

jendeindustries

Bart

MajorBurnz

rajagra

mkornecki

life2short1971

Brownbear

life2short1971

honed

jendeindustries

Similar threads