In a recent post, Sharpening with the King 1k/6k combination stone, I showed one example of burr removal, folding the burr and removing it (at the sharpening angle). In this post, I demonstrate two other techniques for burr removal; stropping and high-angle-passes.
As discussed in What is a burr? part 1 and What is a burr? part 2, There is no unique definition of a knife burr. In general, the term refers to excess, unwanted metal beyond the “ideal” apex; however, the “wanted” metal will depend on how the blade is used and what material is being cut. To aid in demonstrating the length scales and geometries involved, several examples were chosen.
In the first two examples, the starting point was a blade honed to the Shapton 16k, ending with 20 edge-trailing passes. This produces a near-perfect triangle with a small foil-burr at the apex.
Edge-on view of a carbon steel straight razor (16.5 degree included angle) honed to the level of a Shapton 16k with edge leading strokes, then finished with 20 edge-trailing strokes to produce a triangular bevel with a small foil-burr beyond the triangular apex.High magnification, edge-on view of a carbon steel straight razor (16.5 degree included angle) honed to the level of a Shapton 16k with edge leading strokes, then finished with 20 edge-trailing strokes to produce a triangular bevel with a small foil-burr beyond the triangular apex.
In the first example, the apex is micro-convexed by stropping, removing the foil burr plus approximately 7 microns of blade height. The increase in near-apex angle from approximately 16 to 26 degrees (inclusive) significantly improves the durability of the blade. This blade easily shaves, but has minimal draw-cutting aggression, due to the uniformity of the apex.
Edge-on view of the blade following stropping on a hanging denim strop loaded with Mother’s mag polish (aluminum oxide).Edge-on view of the blade following stropping on a hanging denim strop loaded with Mother’s mag polish (aluminum oxide).Cross-section view of the blade following stropping on a hanging denim strop loaded with Mother’s mag polish (aluminum oxide). The near apex angle has increased by 10 degrees to 26 degrees inclusive.Cross-section view of the blade following stropping on a hanging denim strop loaded with Mother’s mag polish (aluminum oxide). The white triangle shows the cross-section of the blade prior to stropping. Approximately 7 microns of blade height has been removed.
In the second example, the blade was given three passes (per side, alternating) on a DMT EF (1200 grit) diamond hone at an angle of 20 degrees. Although minimal force was applied, only sufficient to hold contact, the pressure was extremely high due to the small contact area. Pressure is force/area, and the contact area is only that of the micro-bevel. As a result of this high pressure, there is obvious plastic deformation of the apex.
Edge-on view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate.Edge-on view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate.Cross-section view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate. The near-apex angle has been increased to 40 degrees (20 degrees per side).Cross-section view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate. Approximately 23 microns of blade height has been removed.Side view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate. A micro-bevel, approximately 15 microns wide has been produced.Side view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate.
The above example was performed with a simple carbon steel straight razor. The following are examples from a ZDP-189 pocket knife (Spyderco Manbug).
Edge-on view of a ZDP-189 knife finished with a DMT EF (1200 grit) diamond hone using edge-leading strokes. A subtle burr, too small to see with an optical microscope, is produced.Edge-on view of a ZDP-189 knife finished with a DMT EF (1200 grit) diamond hone using edge-leading strokes, then stropped on a hanging kangaroo leather strop loaded with 0.25 micron poly-diamond. The black film is oily residue from the strop.Edge-on view of a ZDP-189 knife finished with a DMT EF (1200 grit) diamond hone using edge-leading strokes, then stropped on a hanging kangaroo leather strop loaded with 0.25 micron poly-diamond. The initial burr is removed.Edge-on view of a ZDP-189 knife finished with a DMT EF (1200 grit) diamond hone using edge-trailing strokes. A burr, large enough to be visible with an optical microscope is produced.Edge-on view of a ZDP-189 knife finished with a DMT EF (1200 grit) diamond hone using edge-trailing strokes. The burr, shown in the previous image was then (mostly) “broken off” by cutting cross-grain into a piece of redwood.
In comparing the two knife edges, above, the results are as expected. The stropped edge easily shaves and push-cuts paper, but has no draw-cutting aggression and does not pass the 3-finger slide test. The broken-burr edge draw-cuts aggressively and easily passes the 3-finger test, but does not shave or push-cut paper.
I have seen the burr being drawn off/cleaned up by drawing an edge on the end grain of a block of wood, instead of the side grain. Seems like less wear and tear on the edge to draw it across end grain, as the edge gets wedged between fibers instead of trying to slice them crosswise – any thoughts?
I have not tried end-grain specifically. My expectation is that it would still roll the edge, certainly not rip the burr off.
I will add this to the list of things to try…
My straight razor exfoliates skin also after stropping. I think there are strong burr. Is correct using a 12-k making slow and very light strokes first forth and after back to remove burr? Exfoliation is due to burrs or to a incomplete bevel? After the honing on 1000 k the razor must cut easily arm’s hair? Because it cut arm’s just after honing on a 3000k stone!
Thanks for sharing! Why is there no burr on the pocket knife apex after stropping on hanging kangaroo even though you did not produce a micro convex on coarser compound first? Did you reduce the angle a bit for stropping?
There is a nano-scale burr, almost too small to see at these magnifications.
However, compared to the foil edges from a hanging Latigo and diamond strop, this minuscule.
I did strop the knife at a lower angle, on a hanging strop it is not difficult to find an angle that just makes contact with the apex.
Anecdotally, measurements on vintage carbon steel straight razors I have seen are in the range 58-62. Some of the current production blades are reported to be a few points higher.
Ah, I see. They’re just about as hard as Japanese chisel and plane blades.
I had thought that trailing strokes tended to cause the burr to tear off and leave a jagged edge, however your microphotograph studies have demonstrated that the trailing strokes tend to produce a foil edge and the leading strokes produce no burr and chip the edge, especially with coarse stones. Learning a lot here!
The funny bit is that I have some very old (1903) saw sharpening manuals that say exactly what is in these modern pictures. That is trailing edge produces a smoother edge and leaves a bit of burr. Though those were speaking of mill files and edge-leading roughness being caused by chatter/vibration.
Considering that in the convexing with canvas + polish the edge was lowered by 7 microns, wouldn’t it be possible using this procedure to remove very large burrs created for example by honing a straight razor just with edge trailing strokes on a 4k stone? (intuitively if the edge gets micro convexed by such a extent that any foil burr should be removed no matter how large)
What straigh razor honing progression would you recommend for the ham handed, edge leading/trailing, stone grit, considering the edge will be convexed on hanging canvas with paste + hanging leather 0,25 cbn?
Why are you using Mother’s mag polish instead of Thiers Issard white paste, did you find the latter not being suitable any more? How tight are you holding the strop and are you using any pressure, if that affects the degree the edge is convexed?
What influence would have harder steel (some Iwasaki straigth were hardened to 66,5 HRC – Hardness was stamped on the box)?
You are correct, the hanging denim with metal polish seems to remove any foil burr, and provides an easy route to honing a straight razor.
I would suggest the following for anyone having difficulty honing their own straight razor:
This approach should be foolproof if you are honing a straight razor that has been shave-ready (not a restoration or factory edge, for example) and not been damaged (no chips that you can feel with your thumbnail) and is not warped.
If you are unsure, I would suggest raising a burr that you can feel using a 1k stone – I would only do this once, as it is a waste of steel.
Start with the 1k stone, long enough to make black swarf, then ending with about 20 edge trailing strokes. Second to 4k-8k level stone ending with about 20 edge-trailing strokes. There is no need for feather light touch, but the edge trailing strokes should not flex the blade either. This should produce a foil edge – more steel than we want at the apex.
Third, use the hanging denim strop with metal polish. I use a strip about 4cm wide and 20cm long, but you can make it larger if you prefer. As a rule, I do 30 laps. Again, no need for feather light strokes – on a weigh scale I would see about 200g. I normally tape the denim strip to the edge of the bench, and do not pull nearly hard enough to pull it loose. This will micro-convex the blade, removing any foil. I replace the denim strop when it becomes dark and glazed, after maybe ten uses.
The various metal polishes I have analyzed and tested perform similarly. The main difference between them is the lubricants and solvents that act as the carrier for the aluminum oxide abrasive. On denim (or linen) the larger particles become embedded in the weave and do nothing – for this reason it doesn’t matter which one you use ON HANGING DENIM.
Fourth, to clean up the apex and maximize keenness after then denim, strop on 0.25 micron diamond on smooth leather. Again, I do 30 laps as rule.
Finally, prior to shaving, I strop on clean leather, 30-50 laps.
I tried this technique on my SR. It produced a very nice looking edge on my optical scope. The micro convexity was rather appearent on the scope so some questions:
-If you strop first on the pasted strop creating the convexity, THEN go to the balsa with .25 diamond, since the balsa does not compress, is the balsa hitting the apex?
– Does stropping on clean linen and/or leather create a foil edge? I know you said it burnishes or moves metal toward the apex but is it enough to create a foil?
– As long as I’m asking about a foil, if you do create one say doing 20-30 trailing passes on your stone, have you checked to see how many LEADING passes on that same stone it would take to remove it.
Balsa strops are highly variable, depending on the surface finish. When there are loose wood fibers, apex contact should occur on a micro-convex apex. You may notice that the micro-convex apex is approximately one micron above the stropping surface, while wood fibers are typically 20-30 microns in diameter. This is why a balsa strop is not effective if sanded too smooth, or plastered with too much oil-based abrasive.
Stropping on clean leather can create a foil-burr, although it requires hundreds of laps. Stropping on linen may remove the burr with sufficient pressure.
Leading edge passes will micro-chip and remove an edge-trailing foil-burr with just one or two laps at finer grits (>1000). On coarser grits (<1000) metal is removed from the bevel face faster than the apex chips and so a foil-burr can be created along some fraction of the apex.
I followed this method exactly. It was my closest shave yet. My girlfriend commented that my face was less irritated than she’s ever seen it after I shaved.
In my experience, irritation is usually the result of trying to shave with a razor that is not keen enough. I’m glad to hear that this method worked for you. I’ve honed hundreds of razors with this method and it seems foolproof. It’s good to have someone else confirm that it works for them.
let me please stand in line to confirm your method. It works like a charm.
I stopped at the Shapton 8k GS.
Bevel looked free from chips and stria was linear and flawless (digital loupe, cheap one with monitor display).
I applied “Autosol” (in Germany we use it for polishing shiny metals on cars and bikes) on a clean fabric strop and did about 35 laps.
Originally clean white (the fabric as well as the Autosol paste) the strop turned dark grey after about 5 laps.
After that, I used a homemade paddle strop (fine leather) loaded with Dovo / Herold BLACK paste (stick).
Since I have no diamond paste or spray (already ordered), I had to use the BLACK paste.
It is known for it´s much finer polishing abilities than CrOx e. g.
An additional 100 laps on my clean leather strop (Latigo / Juchten) accomplished an extremely comfortable and clean shave.
If I could, I would exchange some comfort for a bit more sharpness. Just for the crisp feeling of a blade hovering over the skin… dunno how to explain otherwise…
Anyway, I never had such a good shave with such easy and cheap materials (stopping at 8K, no 12/16k or more).
Congratulations !!!
It really IS foolproof if done as you described.
And I´m sure there is way more possible, given my first try and the use of the black paste.
One last question:
Could you recommend to exchange the diamond loaded leather for CrOx leather or finer grit paste on leather or would that be a disadvantage / downgrade? (just asking because I´d like to use my loved paste strops in the future as well as the incoming diamond spray)
The effect of the strop is mostly determined by the strop material itself – the abrasive just speeds it up (significantly). In principle chromium oxide works just fine (for carbon steel razors), but I had sometimes had issues with foil-burrs when I was experimenting with it. I don’t recall using it in place of the 0.25 or 0.5 micron diamond in my “simple” honing routine, but it should work.
Great job on all of this. I have many questions but I’ll try and limit it. Are you saying the micro-convex bevel is preferred on a straight razor?
Regarding the foil, I’ve seen and tried cork and like mediums to drag the blade through to remove the foil and finish with stropping. Have you seen, heard of this and have any pics of it?
I think you are aware that there is no consensus on the “preferred” approach to honing a straight razor. Personally, I achieve close and comfortable shaves with a micro-convex bevel.
I have only ever observed a foil to fold or roll when drawn through a non-abrasive medium, but I have not tried cork specifically. The reason that foil edges form is that they do not break easily – it reminds me of the Oak and the Read
I read above that you stated to strop with Mothers on denim to best remove the burr. On another post (I forget which one) you suggested a 10 micron TI paste. Were you talking different things or are they interchangeable?
What about natural stones, coticules, JNATS and the like? Increase likelyhood of foil or no difference. Do you think the coticules have a reputation of being more comfortable because maybe they don’t produce the foil?
Hello, fascinating studies! I’m mostly interested in sharpening knifes rather than razors and there are some examples of knife edges in your articles, but I’m still not sure how to handle it best. Also, my knife sharpening is a ‘field’ affair with minimum of supplies. Would you be kind enough to comment on this general ‘method’?
Grind edge-leading at ~20 degrees one side at the time on ~0.5k Dimond until burr evident – switch sides – some 5-10 strokes per side.
On the same 0.5k diamond, try to remove main burr by light alternating side edge leading strokes at the same 20 deg angle. Maybe 2-3 double passes
Hone edge-leading on ceramic (1-2k I imagine), side alternating, some 10+ passes, same 20 deg angle to form an apex with minimal burr remaining. Finish with 2-3 edge-leading strokes at higher 25 deg angle to remove the residual burr and initiate micro bevel.
Strop on leather on hard surface (a small leather pouch where the Dimond/ceramic combination mini stone is stored) primed with chromium oxide crayon at some 25 deg for some 20+ passes to clean the residual burr, clean the apex, and induce convex shape to the micro bevel.
You cannot remove a burr at the sharpening angle on a diamond plate – you will just stand it up so that you can’t feel it. The ceramic should be able to remove the burr if you increase the sharpening angle above what you used on the diamond plate.
I don’t see any reason your approach wouldn’t work. If you want to experiment, I would suggest lowering the angle on the diamond plate a few degrees, strop at that same angle to minimize the burr., then use your ceramic at 20 degrees, and strop at the same angle. I would always increase pressure on the strop rather than increasing the angle. Then use your ceramic at 20-25 degrees to maintain, just as you would a kitchen knife with a honing rod.
Cheers for that! I’m trying to visualize what a stropping step after mid diamond and before ceramic at slightly larger angle should accomplish. Is it the burr breaking by flipping it back and forth when stropping? What advantage would it have vs. going straight to ceramic? Also, I feel that when I hone by hand I can’t keep the angle to better than a degree, likely a few at least occasionally. Does it mean that for knifes I’m likely to ‘trim’ the burr just by virtue of my inconsistency?
I have not observed any difference between blades stropped on TI paste, Mother’s mag polish or Wenol metal polish (all on hanging denim). In fact, the TI paste was the coarsest of the three when analyzed in the SEM. On hanging denim or similar fabrics, where the large particles can fall into the weave, these seem to be interchangeable. The key is that they all contain a range of particles down to sub-micron.
Missed this when you first posted it. Outstanding blog, as usual. One of my favorite reads, and great images. I look forward to seeing some of the stuff you post regarding the natural stones and the resultant edges.
Todd, in the 5th picture from the bottom after DMT 1200 there is a subtle burr, likely only subtle due to balance of abrasion and microchipping ? If more pressure would have been applied, I guess we would see a bigger burr. Is that because the abrasion “power” increases disproportional to microchipping in your opinion?
I would attribute that burr to the fact that I free-hand sharpened the knife. You are correct that abrasion has occurred fast than micro-chipping, but this results from my inability to hold the (2 inch bladed) knife at at the same angle to better than a half-degree.
For sharpening (kitchen) knives, I use back-and-forth motions.
My left hand is on the blade, defining the main point of contact with the stone, while the right hand is on the knife grip, defining the sharpening angle.
Since I apply most pressure on the pass away from me, this means predominantly edge-leading strokes on one side of the blade, with edge-trailing strokes on the other side.
I am quite happy with this – I remove steel fast, can keep the slurry on the stone and have good control of the sharpening angle ( my main problem so far ). Still, sharpness only reaches acceptable levels with high-grit stones ( 8-12K or naturals ).
From the lecture of your articles and most forums, I suspect that good sharpness should already be achieved at lower grits. So I suspect that I have a burr-related problem.
My question is:
Do you perhaps have any insight about burr-formation using back-and-forth-motions on knifes or ideas how to avoid it ?
Basically, I am looking for a way to leave a stone burr-free and would be glad for any help.
Tried your method for sharpening razors today and achieved better results ( relating to HHT ) on the first try than ever before on my own. Thank you very much!
Back and forth motions are a comfortable and efficient way to remove steel, but once you reach the apex, a burr will form regardless of whether you apply more pressure on the forward stroke. The burr will bend away from the stone and continue to grow unless you increase your angle occasionally (which is hard to avoid with free hand sharpening) and essentially cut the burr by forming a micro-bevel. The reason for alternating sides with edge leading strokes is to minimize this type of burr. Personally, I have had good results with using back and forth strokes to remove steel quickly and then switching to alternating side, edge leading strokes to finish the apex.
Just to be clear – is a micro-bevel necessary for de-burring after back-and-forth strokes ? Or, assuming ( unrealistically, but possibly with sharpening systems ) I would be able to perfectly hold my sharpening angle and not create a micro-bevel, would I still remove the burr by a few alternating edge-leading strokes as suggested?
Since these strokes take a lot of time and are prone to mistakes ( I have to check my angle before every stroke ), I would like to minimise their number. Do you perhaps have any insight in how many are typically necessary ?
The outlook of leaving the coarse stones burr-free and just to create a small burr on a fine stone before stropping it away analogous to Todd´s razor honing is intriguing.
The burr from back-and-forth strokes can be quite large and thick. You would need to do enough edge-leading strokes to cut through the burr and form a new apex. This is obviously easier to accomplish freehand if you raise the angle slightly.
What I do is to alternate sides while doing progressively fewer back-and forth strokes, say 30 then 10 then a few single strokes alternating sides.
Hi,
Great info! I currently use soft balsa and chrox powder
On my straights to finishish with. Will chrox and soft balsawood remove a tiny micro-burr? Will this also introduce some micro convexing to my edge for strength also? Does rock hard felt compress more than balsa? I read about the felts, but I’m not familiar with them.
The balsa will produce micro-convexity just like a denim/linen strop. It is the loose fibres that are responsible for this, not the compression of the strop itself. For felt, it should also be the loose fibres that “do the work” and again compression isn’t that important as long as it isn’t obviously soft.
Okay if i micro convex my straight razor on a foam backed leather paddle strop or a hanging strop, and i decide to go back to another paddle strop hard felt with finer abrasives, would i need to add a layer of tape before going to the felt, so i can hit the summit/tip of the apex. The reason i ask is because i convexed and slightly increased the angle on the foam backed leather strop,(or sometime a hanging strop) so whenever i go to a glued down piece of felt to wood there is no Compression on the felt so i would not be hitting the prior increased angle at the tip i did on the hanging strop or the foam backed leather strop Would i? So would i need to add a layer of tape whenever or if return to more of a flat surface that doesn’t have and ‘give’/compression?
I’ve only ever observed this being necessary on a very smooth balsa strop – the displacement of the apex from the surface due to micro-convexity is much less than the scale of micro-texture on a strop.
I do the same way as Todd, and for kitchen knives you should have a very light touch on the final, only edge leading strokes phase, alternate sides. For longer blades you should manage also to blend all the edge sections, since a full stroke heel to point is often less than pratical (depending on your stone size). With the higher grits i have found the brief edge trailing finishing step, before the strop – as suggested by Todd – is a great improvement.
Compared to the microbevel produced by the DMT EF, the ceramic equivalent will be more uniform. The “toothy” appearance of the DMT EF microbevel is due to the small concentration over-sized diamonds causing deep scratches.
Okay, I made my denim strop today and now have a small chef’s knife that doubles as a razor. I may not use it every time…or even very often. But I wanted to know that I could.
Thank you again!
PS it’s just a strip bent over at each long end and sewn to allow a piece of hanger to hold it at a drawer handle or…
Your observations about burr formation and removal, in respect to the use of leading or trailing strokes with the blade – – do you think the same mechanism would be at work with blades having different (i.e., much more obtuse) edge geometry?
Well, chisels for very hard and brittle woods, if prone to chipping, might be taken to bevel angles as high as 35˚. Plane blades may typically have a bevel angle of anywhere from 38~45˚, however scraping planes can have steeper bevels yet. I guess, for most cases, my question about burr formation and removal applies to blades with a primary bevel between 25˚ and 35˚.
Also, with straight razors, due to the shape of the tool the direction of sharpening is generally going to be crosswise to the length of the blade, however with chisel and plane blades it is also possible to sharpen the blade parallel to the edge. I would be interested in seeing how the burr formation and removal is affected by the difference in direction.
The Japanese woodworker Kunimoto, in one of his sharpening essays, illustrates how the removal of the burr when working the bevel side on a stone, working the edge crosswise (like a straight razor) can result in the burr being torn off, and leaving a jagged edge, when employing trailing strokes. I’d be interested to see if this is an accurate idea or not.
I’m also interested in the idea of jointing the edge as a means of cleaning up damage from burr removal, and how this process can be applied – i.e.,, just once, or at every grit change, just at the beginning, or toward the end of the process, etc..
It’s really valuable to be able to see the edge very close up so as to have a clearer idea as to what is happening with various processes that are otherwise largely invisible to the naked eye. I feel you are doing a great service with this blog.
I meant to say that plane blade bevels can range from as low as 22˚ to as high as 45˚ (and higher fro some scraping tools). The 38˚~45˚ values are bedding angles.
Thanks for the great blog and amazing research. Another knife-user and knife-sharpener here, trying to translate some of the straight razor theory.
I’m interested in all your findings, and am thinking about how to translate them to knives. For my purposes a hanging strop (denim or otherwise) wouldn’t be a desirable solution, so I’m wondering about alternatives.
I typically do my more heavy-duty sharpening on a 1200 grit stone, refine the edge on a 5000, and finish on a 10K naniwa superstone. I do a final strop on paper that I’ve spray-mounted to one of those steel strop holders. The paper is treated with 0.5 micron mono diamond. I haven’t read much about using paper, but it seems to work well, and when it gets dirty I can just replace with another sheet. I’m using some cotton bond paper that doesn’t seem to make a scratch pattern on its own.
One reason I switched to paper was fear that a softer/thicker substrate (like leather) would lead to rounded edges. But your research seems to dismiss this idea. Do you have any thoughts pro or con regarding thin paper glued to metal?
For deburring I’ve been using a piece of “rock-hard felt” sold for the purpose. It magnets to the same strop base. Have you tested anything like this? I use it unloaded, but now I’m wondering if might be a stand-in for a hanging strop if it had compound on it.
I’ve recently been advised by someone who sharpens Japanese knives professionally to put a microbevel on the front side of my gyuto. I have a very thin knife, sharpened with a lot of asymmetry, with bevel angles of 6-7° on each side. It had terrible edge retention. He recommended a thin “hair width” microbevel on just the front side. I’ve interpreted this as about 0.1mm, which is of course gargantuan when judged by the scale of your pics.
This has been helping—with no noticeable loss of performance. But I still suspect I have some wire edge issues. I assumed the microbevel and the stropping and the felt would eliminate this issue, but your research suggests otherwise.
Sorry for the long and rambling post. I’m open to all your ideas.
I would suggest you are suffering from the usual irrational fear of convexity. When we strop correctly we are simply making the blade keener by introducing a tiny amount of convexity in the last few microns of the apex. There is no way around this fact, that stropping increases the bevel angle near the apex. You are not avoiding this angle increase by using thin paper on a hard flat surface. If you use a surface that is too hard, you must use more force or a higher angle to achieve the purpose of stropping. Without some “wrap around” there is no burr removal.
I have shown that the blade only needs to “sink in” to the compressible material a fraction of a micron deep, and you will do this on paper or rock hard felt just as easily as on a hanging denim strop. I believe that a hanging strop is much easier to control for the same reason that it’s more comfortable to lay in a hammock than on a wood floor, but that analogy seems very difficult for most people to accept.
In my experience, an apex with a 15 degree (inclusive) angle cannot cut paper without being damaged. So I would agree that you need to increase the angle near the apex. This can be easily be achieved by stropping on a loaded hanging strop (You would hold the blade flat to the strop as with a straight razor and use the force and strop slack to control the amount). It is more challenging to create a burr-free microbevel because your low angle apex will likely flex away from the stone instead of abrading (this is why micro-bevels don’t work on straight razors). Of course you can combine the two and use the strop to remove any burr left by the microbevel.
#1 may not remove a burr if you use a fine stone. You could first gently “cut into” the stone to be certain of removing the burr by forming a slightly blunted apex and then use the fine stone (or smooth honing steel) at high angle to form a new apex.
#2 essentially takes you to a “known” geometry where you can slowly approach a clean apex – obviously this relies on some skill if you are free-hand sharpening.
Todd, Thank you for all the information you have shared. I have translated what I learnt to knife sharpening using my own jig and the results are both quite amazingly keen but also quick to produce. I did a laminated light vegetable cleaver at 14deg per side and shaved my face albeit not perfectly smooth. My son visited the next day so I had him do a hht with it. It passed HHT-2. You should have seen the smile on his face! Thanks, Jack
I have found these examples and effective, to minimize and remove burrs, on the stones is to do a slight back hone motion before going forward/edge leading.. You are drawing out the burr with the slight back hone, then when you proceed forward you will in some sense abrade off any artifacts.
Also if the burr is on ‘one’ side do very very light edge leading strokes (not enough pressure to flip the burr over) to abrade off the burr/fin, before it flip flops over.
One can do mix it up and do 2 edge trailing passed and then do 8 edge leading, until the burr is gone…
I have seen some people to lateral pull stoke off the side of the stones, but IMO that just tares of the burr, and will leave a ragged edge, and leave a weird scratch patterns.
Dear sir,
I usually sharpen blades by rubbing the abrasive in the direction of the apex towards the body, as I believe that the “leaf” will not form, but I can’t verify, because I don’t have an SEM !!! I imagine that the deformation of the material would drive the thin edges in the opposite direction, not allowing burrs to form. Have you experienced this? I always get sharper blades this way.
Thank you for your attention !
Cláudio Coelho – São Paulo – Brazil
I presume that you are talking about knife blades.
What you describe is usually called “edge leading” sharpening, and as your experience confirms, it creates less of a burr than going the other way – This can be visually confirmed without an SEM, just with a strong loupe or a low power optical microscope.
However, a very small burr is nearly always created and if edge leading, it tends to fold over and become part of the apex. At times, even at 50x magnification it can be barely visible, but is enough to downgrade the edge to some extent. In my experience, to counter this, it is better to finish with edge trailing passes on the stone.
My limited experience kind of confirms with what you say about finishing with edge trailing on the stone for the keenest edge.
Some years ago when I started a free hand sharpening, I only did edge trailing when finishing following Murray Carter’s sharpening instruction. I found my edge extremely sharp but dull a second after cutting anything. After reading Todd’s experiments, I switched to edge leading only and I always use a very light pressure. The edge is more durable but not as keen as when it’s finished with edge trailing. So, my current best method is to do edge leading at a slightly higher angle to make sure that I abrade off the burr as much as possible and do a limited strokes of edge trailing to improve the keenness without creating a wire edge.
Now my challenge is when to stop to get the keenest edge without creating a wire edge or a burr.
What I have found is that some steels and abrasive combinations have a much greater propensity for burr formation than others. I think that this in part has to do with hardness, in part with the amount of retained austenite, and as well as the abrasive used. In my experience diamond stones generate the least burr, possibly because they require the lowest pressure to cut.
In many instances, if alternating edge leading (EL) strokes from side to side, a burr fold over can occur and go unnoticed unless the edge is inspected optically after every stone in the progression.
One way around this is to sharpen EL and do only one side, stop remove any burr formed by cutting into felt or something else, and then do the other side and repeat.
For finishing your suggestion of EL and increasing the angle slightly is one way to go or else a small number of passes with edge trailing when the stage of alternating side to side passes has been reached. As you so rightly say, the challenge is knowing when to stop.
Again in my experience, stones will always generate some burr and its complete removal requires stropping. Here the question becomes whether the additional time spent stropping can be justified in terms of the envisaged use.
I just bought a leather strop and some 1 micron aluminium oxide powder and tried it. I have to say that I haven’t got much success yet. Under my finger pads I felt that my knife was a little duller or maybe it was actually the true clean apex without a burr or a wire edge, I’m not sure. Guess I have to practice more, but as of now I may stick with stone-only sharpening method.
You last question made me rethink about my plan of buying an 8000-grit stone as I already have Naniwa Pro 3000. It’s really just to satisfy my curiousity about the differences of the edge finish and sharpness gain. Whether it’s worth the additional time and money spent or not, I would say that for me it might not.
Do you have access to a low power microscope, or at least a high power loupe? To my mind they are just about essential for determining whether a particular step in the sharpening process works or not.
In sharpening there are a lot of factors at play and sorting out what is going on can be quite a task.
Have you tried the jointing technique (grind the edge on the stone) and doing a few laps of edge leading or edge trailing? Wonder how the results under the microscope would be.
I have recently tried it pretty extensively and I found that most of the times I got a smoother and stronger edge. However, before jointing, I have to make sure that I have really reached the apex and probably created a little wire edge, so that when jointing, the edge isn’t too dull to bring back with a few laps of edge leading or edge trailing (I cheated the risk of using too much pressure when jointing by grinding the knife the side of the stone instead). The challenge is still knowing when to stop doing edge trailing before creating another burr or wire edge.
Yes, I have been experimenting with cutting into the edge of a stone for quite a few years. I find it is much more effective than jointing and avoids any lateral forces. The downside is that does damage the stone, so I tend to use junk stones like the King 1k/6k or one of those naguras that often come with premium stones.
The important thing to know is that the amount of steel removed is quite small – it removes the burr and leave you with a uniformly rounded edge with a radius of 1-2 microns – easily micro-beveled from that point.
I think I have missed something in your writing. Which is much more effective than jointing? Is it cutting into the edge of a stone? I thought cutting into the edge of a stone is similar to jointing.
After having done some more jointing, I have found that the results are not consistent (sometimes I get quite a sharp edge after a few edge leading or edge trailing strokes, sometimes I need to resharpen the knife to get the edge back to a sufficient level of sharpness). And I definitely have to put a micro bevel on to get the edge back to the sharpness I wanted. So in the end, I get a probably stronger and cleaner but less sharp edge. I suspect that the inconsistent results might be due to not producing enough foil edge. I think your simple-straight-razor-honing method might be the way for me to go as it produces a lot more consistent results and definitely sharper edge. However, I don’t have a denim strop, I only have a leather strop. Will a leather strop loaded with 1-2 microns aluminium oxide compound reduce a chance of not getting rid of a foil burr as you show in Simple Straight Razor Honing by stropping with 0.5 micron diamond compound?
Speaking of traditional steels (not S110V) jointing and cutting into the edge of a fine stone (King 6k or Shapton 8k) remove far less steel than you might imagine. Lightly jointing (rubbing the edge on the surface ) just doesn’t remove enough steel to make the edge uniform and slightly blunted. You really need to make several visible cuts into the edge of the stone. See for example the last 3 images in what does steeling do? part 1
After cutting into the stone you would need to remove 1-2 microns from each bevel side to reach the apex if you stay at the same sharpening angle. This is too much for a very fine stone. However, if you increase the angle to microbevel, a very fine stone can easily remove enough steel to reach the apex. A honing rod also easily removes enough steel to reach the apex from this point. Stropping will not restore the apex from this level of dullness.
You can replace the denim strop with paper or cardboard, work the metal polish in with the spine or a screwdriver shank before using it on the blade edge.
How negligent I am to have missed the test you have done. I should have read it long time ago, but I intentionally skipped as I didn’t steel knives. In that test, you cut the Olfa blade, which had an excellent edge into the stone (I really wish I could make an edge like that. Looks like the blade was finished with 0.5 or 0.25 micron strop). I suspect that if I draw out some foil edge, grinding the edge super lightly into the side of the stone might blunt the apex even less. But all in all, seems like if I want the cleanest edge as much as possible, micro convexing or micro bevelling couldn’t be avoided.
I might have missed some tests you did again. What is the difference between using paper or cardboard for strop vs leather? Will paper or cardboard minimize a burr better than leather? And I guess paper is uncompressible, whereas cardboard is compressible? Are majority of jeans made of denim? The labels of most of jeans that I have written 100% cotton. If they are denim, I might try stropping on some old jeans.
Paper or cardboard is a substitute for denim, not leather. The mechanism by which a strop can gently come over the edge and produce micro-convexity comes from the loose fibers on the surface, not the compressibility of the bulk substrate. So paper or cardboard (card stock) are ideal – I would avoid corrugated cardboard.
The denim I use is just strips from some old cotton Levis – a smooth cotton twill kitchen towel should also work. The key is that it has opening/depressions that can absorb the larger abrasive particles in the metal polish. It’s the same principle as to why we use a soft cloth to polish silverware, except the strop must not be stretchy.
Ok, I will try a cardboard or denim. Do you normally using the same method (straight razor honing) to sharpen other types of knives (kitchen, fixed blade, folding, etc.)?
I have tried stropping my kitchen knives on pasted hanging denim and the results seem very good. The edge is very smooth when I touch it with my finger, but it can whittle some hair off my leg (not sure if rounded edge will also be able to whittle hair).
This is the first time I tried stropping on a hanging material. Although the result is very positive, I’m not sure what angle I should hold the knife at when stropping? I laid it quite flat to the denim but not totally flat, maybe like 3-5 degrees. If I strop with the same angle as I sharpen, will that round off the edge?
scienceofsharp 
73 responses to “Burr Removal – part 1”
I have seen the burr being drawn off/cleaned up by drawing an edge on the end grain of a block of wood, instead of the side grain. Seems like less wear and tear on the edge to draw it across end grain, as the edge gets wedged between fibers instead of trying to slice them crosswise – any thoughts?
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I have not tried end-grain specifically. My expectation is that it would still roll the edge, certainly not rip the burr off.
I will add this to the list of things to try…
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This has seemingly worked for me too. If the edge were rolled rather than the burr removed, would that edge cut newsprint cleanly and quietly?
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My straight razor exfoliates skin also after stropping. I think there are strong burr. Is correct using a 12-k making slow and very light strokes first forth and after back to remove burr? Exfoliation is due to burrs or to a incomplete bevel? After the honing on 1000 k the razor must cut easily arm’s hair? Because it cut arm’s just after honing on a 3000k stone!
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Thanks for sharing! Why is there no burr on the pocket knife apex after stropping on hanging kangaroo even though you did not produce a micro convex on coarser compound first? Did you reduce the angle a bit for stropping?
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There is a nano-scale burr, almost too small to see at these magnifications.
However, compared to the foil edges from a hanging Latigo and diamond strop, this minuscule.
I did strop the knife at a lower angle, on a hanging strop it is not difficult to find an angle that just makes contact with the apex.
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What is the typical Rockwell hardness of a straight razor?
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Anecdotally, measurements on vintage carbon steel straight razors I have seen are in the range 58-62. Some of the current production blades are reported to be a few points higher.
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Ah, I see. They’re just about as hard as Japanese chisel and plane blades.
I had thought that trailing strokes tended to cause the burr to tear off and leave a jagged edge, however your microphotograph studies have demonstrated that the trailing strokes tend to produce a foil edge and the leading strokes produce no burr and chip the edge, especially with coarse stones. Learning a lot here!
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The funny bit is that I have some very old (1903) saw sharpening manuals that say exactly what is in these modern pictures. That is trailing edge produces a smoother edge and leaves a bit of burr. Though those were speaking of mill files and edge-leading roughness being caused by chatter/vibration.
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The work you are doing it is incredibly valuable.
Thank you very much for sharing with us
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Considering that in the convexing with canvas + polish the edge was lowered by 7 microns, wouldn’t it be possible using this procedure to remove very large burrs created for example by honing a straight razor just with edge trailing strokes on a 4k stone? (intuitively if the edge gets micro convexed by such a extent that any foil burr should be removed no matter how large)
What straigh razor honing progression would you recommend for the ham handed, edge leading/trailing, stone grit, considering the edge will be convexed on hanging canvas with paste + hanging leather 0,25 cbn?
Why are you using Mother’s mag polish instead of Thiers Issard white paste, did you find the latter not being suitable any more? How tight are you holding the strop and are you using any pressure, if that affects the degree the edge is convexed?
What influence would have harder steel (some Iwasaki straigth were hardened to 66,5 HRC – Hardness was stamped on the box)?
Thanks a lot!!
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You are correct, the hanging denim with metal polish seems to remove any foil burr, and provides an easy route to honing a straight razor.
I would suggest the following for anyone having difficulty honing their own straight razor:
This approach should be foolproof if you are honing a straight razor that has been shave-ready (not a restoration or factory edge, for example) and not been damaged (no chips that you can feel with your thumbnail) and is not warped.
If you are unsure, I would suggest raising a burr that you can feel using a 1k stone – I would only do this once, as it is a waste of steel.
Start with the 1k stone, long enough to make black swarf, then ending with about 20 edge trailing strokes. Second to 4k-8k level stone ending with about 20 edge-trailing strokes. There is no need for feather light touch, but the edge trailing strokes should not flex the blade either. This should produce a foil edge – more steel than we want at the apex.
Third, use the hanging denim strop with metal polish. I use a strip about 4cm wide and 20cm long, but you can make it larger if you prefer. As a rule, I do 30 laps. Again, no need for feather light strokes – on a weigh scale I would see about 200g. I normally tape the denim strip to the edge of the bench, and do not pull nearly hard enough to pull it loose. This will micro-convex the blade, removing any foil. I replace the denim strop when it becomes dark and glazed, after maybe ten uses.
The various metal polishes I have analyzed and tested perform similarly. The main difference between them is the lubricants and solvents that act as the carrier for the aluminum oxide abrasive. On denim (or linen) the larger particles become embedded in the weave and do nothing – for this reason it doesn’t matter which one you use ON HANGING DENIM.
Fourth, to clean up the apex and maximize keenness after then denim, strop on 0.25 micron diamond on smooth leather. Again, I do 30 laps as rule.
Finally, prior to shaving, I strop on clean leather, 30-50 laps.
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I tried this technique on my SR. It produced a very nice looking edge on my optical scope. The micro convexity was rather appearent on the scope so some questions:
-If you strop first on the pasted strop creating the convexity, THEN go to the balsa with .25 diamond, since the balsa does not compress, is the balsa hitting the apex?
– Does stropping on clean linen and/or leather create a foil edge? I know you said it burnishes or moves metal toward the apex but is it enough to create a foil?
– As long as I’m asking about a foil, if you do create one say doing 20-30 trailing passes on your stone, have you checked to see how many LEADING passes on that same stone it would take to remove it.
Thanks for your time.
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Balsa strops are highly variable, depending on the surface finish. When there are loose wood fibers, apex contact should occur on a micro-convex apex. You may notice that the micro-convex apex is approximately one micron above the stropping surface, while wood fibers are typically 20-30 microns in diameter. This is why a balsa strop is not effective if sanded too smooth, or plastered with too much oil-based abrasive.
Stropping on clean leather can create a foil-burr, although it requires hundreds of laps. Stropping on linen may remove the burr with sufficient pressure.
Leading edge passes will micro-chip and remove an edge-trailing foil-burr with just one or two laps at finer grits (>1000). On coarser grits (<1000) metal is removed from the bevel face faster than the apex chips and so a foil-burr can be created along some fraction of the apex.
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I followed this method exactly. It was my closest shave yet. My girlfriend commented that my face was less irritated than she’s ever seen it after I shaved.
Thank you so much.
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In my experience, irritation is usually the result of trying to shave with a razor that is not keen enough. I’m glad to hear that this method worked for you. I’ve honed hundreds of razors with this method and it seems foolproof. It’s good to have someone else confirm that it works for them.
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Hey there,
let me please stand in line to confirm your method. It works like a charm.
I stopped at the Shapton 8k GS.
Bevel looked free from chips and stria was linear and flawless (digital loupe, cheap one with monitor display).
I applied “Autosol” (in Germany we use it for polishing shiny metals on cars and bikes) on a clean fabric strop and did about 35 laps.
Originally clean white (the fabric as well as the Autosol paste) the strop turned dark grey after about 5 laps.
After that, I used a homemade paddle strop (fine leather) loaded with Dovo / Herold BLACK paste (stick).
Since I have no diamond paste or spray (already ordered), I had to use the BLACK paste.
It is known for it´s much finer polishing abilities than CrOx e. g.
An additional 100 laps on my clean leather strop (Latigo / Juchten) accomplished an extremely comfortable and clean shave.
If I could, I would exchange some comfort for a bit more sharpness. Just for the crisp feeling of a blade hovering over the skin… dunno how to explain otherwise…
Anyway, I never had such a good shave with such easy and cheap materials (stopping at 8K, no 12/16k or more).
Congratulations !!!
It really IS foolproof if done as you described.
And I´m sure there is way more possible, given my first try and the use of the black paste.
One last question:
Could you recommend to exchange the diamond loaded leather for CrOx leather or finer grit paste on leather or would that be a disadvantage / downgrade? (just asking because I´d like to use my loved paste strops in the future as well as the incoming diamond spray)
Greetings from Germany,
Boris
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The effect of the strop is mostly determined by the strop material itself – the abrasive just speeds it up (significantly). In principle chromium oxide works just fine (for carbon steel razors), but I had sometimes had issues with foil-burrs when I was experimenting with it. I don’t recall using it in place of the 0.25 or 0.5 micron diamond in my “simple” honing routine, but it should work.
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Great job on all of this. I have many questions but I’ll try and limit it. Are you saying the micro-convex bevel is preferred on a straight razor?
Regarding the foil, I’ve seen and tried cork and like mediums to drag the blade through to remove the foil and finish with stropping. Have you seen, heard of this and have any pics of it?
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I think you are aware that there is no consensus on the “preferred” approach to honing a straight razor. Personally, I achieve close and comfortable shaves with a micro-convex bevel.
I have only ever observed a foil to fold or roll when drawn through a non-abrasive medium, but I have not tried cork specifically. The reason that foil edges form is that they do not break easily – it reminds me of the Oak and the Read
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I read above that you stated to strop with Mothers on denim to best remove the burr. On another post (I forget which one) you suggested a 10 micron TI paste. Were you talking different things or are they interchangeable?
What about natural stones, coticules, JNATS and the like? Increase likelyhood of foil or no difference. Do you think the coticules have a reputation of being more comfortable because maybe they don’t produce the foil?
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Hello, fascinating studies! I’m mostly interested in sharpening knifes rather than razors and there are some examples of knife edges in your articles, but I’m still not sure how to handle it best. Also, my knife sharpening is a ‘field’ affair with minimum of supplies. Would you be kind enough to comment on this general ‘method’?
Grind edge-leading at ~20 degrees one side at the time on ~0.5k Dimond until burr evident – switch sides – some 5-10 strokes per side.
On the same 0.5k diamond, try to remove main burr by light alternating side edge leading strokes at the same 20 deg angle. Maybe 2-3 double passes
Hone edge-leading on ceramic (1-2k I imagine), side alternating, some 10+ passes, same 20 deg angle to form an apex with minimal burr remaining. Finish with 2-3 edge-leading strokes at higher 25 deg angle to remove the residual burr and initiate micro bevel.
Strop on leather on hard surface (a small leather pouch where the Dimond/ceramic combination mini stone is stored) primed with chromium oxide crayon at some 25 deg for some 20+ passes to clean the residual burr, clean the apex, and induce convex shape to the micro bevel.
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You cannot remove a burr at the sharpening angle on a diamond plate – you will just stand it up so that you can’t feel it. The ceramic should be able to remove the burr if you increase the sharpening angle above what you used on the diamond plate.
I don’t see any reason your approach wouldn’t work. If you want to experiment, I would suggest lowering the angle on the diamond plate a few degrees, strop at that same angle to minimize the burr., then use your ceramic at 20 degrees, and strop at the same angle. I would always increase pressure on the strop rather than increasing the angle. Then use your ceramic at 20-25 degrees to maintain, just as you would a kitchen knife with a honing rod.
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Cheers for that! I’m trying to visualize what a stropping step after mid diamond and before ceramic at slightly larger angle should accomplish. Is it the burr breaking by flipping it back and forth when stropping? What advantage would it have vs. going straight to ceramic? Also, I feel that when I hone by hand I can’t keep the angle to better than a degree, likely a few at least occasionally. Does it mean that for knifes I’m likely to ‘trim’ the burr just by virtue of my inconsistency?
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I have not observed any difference between blades stropped on TI paste, Mother’s mag polish or Wenol metal polish (all on hanging denim). In fact, the TI paste was the coarsest of the three when analyzed in the SEM. On hanging denim or similar fabrics, where the large particles can fall into the weave, these seem to be interchangeable. The key is that they all contain a range of particles down to sub-micron.
I will explain natural stones someday…
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Todd!
Missed this when you first posted it. Outstanding blog, as usual. One of my favorite reads, and great images. I look forward to seeing some of the stuff you post regarding the natural stones and the resultant edges.
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Thanks Eric.
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Todd, in the 5th picture from the bottom after DMT 1200 there is a subtle burr, likely only subtle due to balance of abrasion and microchipping ? If more pressure would have been applied, I guess we would see a bigger burr. Is that because the abrasion “power” increases disproportional to microchipping in your opinion?
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I would attribute that burr to the fact that I free-hand sharpened the knife. You are correct that abrasion has occurred fast than micro-chipping, but this results from my inability to hold the (2 inch bladed) knife at at the same angle to better than a half-degree.
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I was also wondering if you would get similar results with a denim on paddle strop, instead of the hanging strop?
Thanks, Matt.
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This is a very complex issue, but the short answer is no. I will discuss hanging vs paddle strops at some point in the future.
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We need this
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For sharpening (kitchen) knives, I use back-and-forth motions.
My left hand is on the blade, defining the main point of contact with the stone, while the right hand is on the knife grip, defining the sharpening angle.
Since I apply most pressure on the pass away from me, this means predominantly edge-leading strokes on one side of the blade, with edge-trailing strokes on the other side.
I am quite happy with this – I remove steel fast, can keep the slurry on the stone and have good control of the sharpening angle ( my main problem so far ). Still, sharpness only reaches acceptable levels with high-grit stones ( 8-12K or naturals ).
From the lecture of your articles and most forums, I suspect that good sharpness should already be achieved at lower grits. So I suspect that I have a burr-related problem.
My question is:
Do you perhaps have any insight about burr-formation using back-and-forth-motions on knifes or ideas how to avoid it ?
Basically, I am looking for a way to leave a stone burr-free and would be glad for any help.
Tried your method for sharpening razors today and achieved better results ( relating to HHT ) on the first try than ever before on my own. Thank you very much!
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Back and forth motions are a comfortable and efficient way to remove steel, but once you reach the apex, a burr will form regardless of whether you apply more pressure on the forward stroke. The burr will bend away from the stone and continue to grow unless you increase your angle occasionally (which is hard to avoid with free hand sharpening) and essentially cut the burr by forming a micro-bevel. The reason for alternating sides with edge leading strokes is to minimize this type of burr. Personally, I have had good results with using back and forth strokes to remove steel quickly and then switching to alternating side, edge leading strokes to finish the apex.
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Thanks very much for yours and Stefanos answers.
Just to be clear – is a micro-bevel necessary for de-burring after back-and-forth strokes ? Or, assuming ( unrealistically, but possibly with sharpening systems ) I would be able to perfectly hold my sharpening angle and not create a micro-bevel, would I still remove the burr by a few alternating edge-leading strokes as suggested?
Since these strokes take a lot of time and are prone to mistakes ( I have to check my angle before every stroke ), I would like to minimise their number. Do you perhaps have any insight in how many are typically necessary ?
The outlook of leaving the coarse stones burr-free and just to create a small burr on a fine stone before stropping it away analogous to Todd´s razor honing is intriguing.
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The burr from back-and-forth strokes can be quite large and thick. You would need to do enough edge-leading strokes to cut through the burr and form a new apex. This is obviously easier to accomplish freehand if you raise the angle slightly.
What I do is to alternate sides while doing progressively fewer back-and forth strokes, say 30 then 10 then a few single strokes alternating sides.
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Hi,
Great info! I currently use soft balsa and chrox powder
On my straights to finishish with. Will chrox and soft balsawood remove a tiny micro-burr? Will this also introduce some micro convexing to my edge for strength also? Does rock hard felt compress more than balsa? I read about the felts, but I’m not familiar with them.
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The balsa will produce micro-convexity just like a denim/linen strop. It is the loose fibres that are responsible for this, not the compression of the strop itself. For felt, it should also be the loose fibres that “do the work” and again compression isn’t that important as long as it isn’t obviously soft.
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Okay if i micro convex my straight razor on a foam backed leather paddle strop or a hanging strop, and i decide to go back to another paddle strop hard felt with finer abrasives, would i need to add a layer of tape before going to the felt, so i can hit the summit/tip of the apex. The reason i ask is because i convexed and slightly increased the angle on the foam backed leather strop,(or sometime a hanging strop) so whenever i go to a glued down piece of felt to wood there is no Compression on the felt so i would not be hitting the prior increased angle at the tip i did on the hanging strop or the foam backed leather strop Would i? So would i need to add a layer of tape whenever or if return to more of a flat surface that doesn’t have and ‘give’/compression?
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I’ve only ever observed this being necessary on a very smooth balsa strop – the displacement of the apex from the surface due to micro-convexity is much less than the scale of micro-texture on a strop.
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I do the same way as Todd, and for kitchen knives you should have a very light touch on the final, only edge leading strokes phase, alternate sides. For longer blades you should manage also to blend all the edge sections, since a full stroke heel to point is often less than pratical (depending on your stone size). With the higher grits i have found the brief edge trailing finishing step, before the strop – as suggested by Todd – is a great improvement.
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Todd, do you think doing the light microbevel strokes on a medium ceramic for instance would yield different results?
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Compared to the microbevel produced by the DMT EF, the ceramic equivalent will be more uniform. The “toothy” appearance of the DMT EF microbevel is due to the small concentration over-sized diamonds causing deep scratches.
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Okay, I made my denim strop today and now have a small chef’s knife that doubles as a razor. I may not use it every time…or even very often. But I wanted to know that I could.
Thank you again!
PS it’s just a strip bent over at each long end and sewn to allow a piece of hanger to hold it at a drawer handle or…
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Your observations about burr formation and removal, in respect to the use of leading or trailing strokes with the blade – – do you think the same mechanism would be at work with blades having different (i.e., much more obtuse) edge geometry?
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This is a good question, and one that I would like to study systematically at some point.
The mechanism is mainly due to steel at the apex either bending or breaking (chipping) rather than being cut clean through.
The effect always occurs with 15-20 degree apex angles and never occurs with 90 degree “apex” angles.
The largest angle I can recall using for sharpening would be 30 degrees (for my chisels) – are you thinking of angles more obtuse than this?
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Well, chisels for very hard and brittle woods, if prone to chipping, might be taken to bevel angles as high as 35˚. Plane blades may typically have a bevel angle of anywhere from 38~45˚, however scraping planes can have steeper bevels yet. I guess, for most cases, my question about burr formation and removal applies to blades with a primary bevel between 25˚ and 35˚.
Also, with straight razors, due to the shape of the tool the direction of sharpening is generally going to be crosswise to the length of the blade, however with chisel and plane blades it is also possible to sharpen the blade parallel to the edge. I would be interested in seeing how the burr formation and removal is affected by the difference in direction.
The Japanese woodworker Kunimoto, in one of his sharpening essays, illustrates how the removal of the burr when working the bevel side on a stone, working the edge crosswise (like a straight razor) can result in the burr being torn off, and leaving a jagged edge, when employing trailing strokes. I’d be interested to see if this is an accurate idea or not.
I’m also interested in the idea of jointing the edge as a means of cleaning up damage from burr removal, and how this process can be applied – i.e.,, just once, or at every grit change, just at the beginning, or toward the end of the process, etc..
It’s really valuable to be able to see the edge very close up so as to have a clearer idea as to what is happening with various processes that are otherwise largely invisible to the naked eye. I feel you are doing a great service with this blog.
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I meant to say that plane blade bevels can range from as low as 22˚ to as high as 45˚ (and higher fro some scraping tools). The 38˚~45˚ values are bedding angles.
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Thanks for the great blog and amazing research. Another knife-user and knife-sharpener here, trying to translate some of the straight razor theory.
I’m interested in all your findings, and am thinking about how to translate them to knives. For my purposes a hanging strop (denim or otherwise) wouldn’t be a desirable solution, so I’m wondering about alternatives.
I typically do my more heavy-duty sharpening on a 1200 grit stone, refine the edge on a 5000, and finish on a 10K naniwa superstone. I do a final strop on paper that I’ve spray-mounted to one of those steel strop holders. The paper is treated with 0.5 micron mono diamond. I haven’t read much about using paper, but it seems to work well, and when it gets dirty I can just replace with another sheet. I’m using some cotton bond paper that doesn’t seem to make a scratch pattern on its own.
One reason I switched to paper was fear that a softer/thicker substrate (like leather) would lead to rounded edges. But your research seems to dismiss this idea. Do you have any thoughts pro or con regarding thin paper glued to metal?
For deburring I’ve been using a piece of “rock-hard felt” sold for the purpose. It magnets to the same strop base. Have you tested anything like this? I use it unloaded, but now I’m wondering if might be a stand-in for a hanging strop if it had compound on it.
I’ve recently been advised by someone who sharpens Japanese knives professionally to put a microbevel on the front side of my gyuto. I have a very thin knife, sharpened with a lot of asymmetry, with bevel angles of 6-7° on each side. It had terrible edge retention. He recommended a thin “hair width” microbevel on just the front side. I’ve interpreted this as about 0.1mm, which is of course gargantuan when judged by the scale of your pics.
This has been helping—with no noticeable loss of performance. But I still suspect I have some wire edge issues. I assumed the microbevel and the stropping and the felt would eliminate this issue, but your research suggests otherwise.
Sorry for the long and rambling post. I’m open to all your ideas.
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I would suggest you are suffering from the usual irrational fear of convexity. When we strop correctly we are simply making the blade keener by introducing a tiny amount of convexity in the last few microns of the apex. There is no way around this fact, that stropping increases the bevel angle near the apex. You are not avoiding this angle increase by using thin paper on a hard flat surface. If you use a surface that is too hard, you must use more force or a higher angle to achieve the purpose of stropping. Without some “wrap around” there is no burr removal.
I have shown that the blade only needs to “sink in” to the compressible material a fraction of a micron deep, and you will do this on paper or rock hard felt just as easily as on a hanging denim strop. I believe that a hanging strop is much easier to control for the same reason that it’s more comfortable to lay in a hammock than on a wood floor, but that analogy seems very difficult for most people to accept.
In my experience, an apex with a 15 degree (inclusive) angle cannot cut paper without being damaged. So I would agree that you need to increase the angle near the apex. This can be easily be achieved by stropping on a loaded hanging strop (You would hold the blade flat to the strop as with a straight razor and use the force and strop slack to control the amount). It is more challenging to create a burr-free microbevel because your low angle apex will likely flex away from the stone instead of abrading (this is why micro-bevels don’t work on straight razors). Of course you can combine the two and use the strop to remove any burr left by the microbevel.
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After reading you post i wanted to ask – high angle (1-3 light passes) seem to leave the edge a little damaged.
Options:
1/ Do this on a finer stone (Diamond is too course/aggressive)?
2/ And/or back-sharpen at original angle to refine the edge again?
Thoughts?
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I think both will work.
#1 may not remove a burr if you use a fine stone. You could first gently “cut into” the stone to be certain of removing the burr by forming a slightly blunted apex and then use the fine stone (or smooth honing steel) at high angle to form a new apex.
#2 essentially takes you to a “known” geometry where you can slowly approach a clean apex – obviously this relies on some skill if you are free-hand sharpening.
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Todd, Thank you for all the information you have shared. I have translated what I learnt to knife sharpening using my own jig and the results are both quite amazingly keen but also quick to produce. I did a laminated light vegetable cleaver at 14deg per side and shaved my face albeit not perfectly smooth. My son visited the next day so I had him do a hht with it. It passed HHT-2. You should have seen the smile on his face! Thanks, Jack
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I have found these examples and effective, to minimize and remove burrs, on the stones is to do a slight back hone motion before going forward/edge leading.. You are drawing out the burr with the slight back hone, then when you proceed forward you will in some sense abrade off any artifacts.
Also if the burr is on ‘one’ side do very very light edge leading strokes (not enough pressure to flip the burr over) to abrade off the burr/fin, before it flip flops over.
One can do mix it up and do 2 edge trailing passed and then do 8 edge leading, until the burr is gone…
I have seen some people to lateral pull stoke off the side of the stones, but IMO that just tares of the burr, and will leave a ragged edge, and leave a weird scratch patterns.
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Dear sir,
I usually sharpen blades by rubbing the abrasive in the direction of the apex towards the body, as I believe that the “leaf” will not form, but I can’t verify, because I don’t have an SEM !!! I imagine that the deformation of the material would drive the thin edges in the opposite direction, not allowing burrs to form. Have you experienced this? I always get sharper blades this way.
Thank you for your attention !
Cláudio Coelho – São Paulo – Brazil
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Hi Claudio,
I presume that you are talking about knife blades.
What you describe is usually called “edge leading” sharpening, and as your experience confirms, it creates less of a burr than going the other way – This can be visually confirmed without an SEM, just with a strong loupe or a low power optical microscope.
However, a very small burr is nearly always created and if edge leading, it tends to fold over and become part of the apex. At times, even at 50x magnification it can be barely visible, but is enough to downgrade the edge to some extent. In my experience, to counter this, it is better to finish with edge trailing passes on the stone.
Cheers
John
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Hi John
My limited experience kind of confirms with what you say about finishing with edge trailing on the stone for the keenest edge.
Some years ago when I started a free hand sharpening, I only did edge trailing when finishing following Murray Carter’s sharpening instruction. I found my edge extremely sharp but dull a second after cutting anything. After reading Todd’s experiments, I switched to edge leading only and I always use a very light pressure. The edge is more durable but not as keen as when it’s finished with edge trailing. So, my current best method is to do edge leading at a slightly higher angle to make sure that I abrade off the burr as much as possible and do a limited strokes of edge trailing to improve the keenness without creating a wire edge.
Now my challenge is when to stop to get the keenest edge without creating a wire edge or a burr.
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Hi Blgg,
What I have found is that some steels and abrasive combinations have a much greater propensity for burr formation than others. I think that this in part has to do with hardness, in part with the amount of retained austenite, and as well as the abrasive used. In my experience diamond stones generate the least burr, possibly because they require the lowest pressure to cut.
In many instances, if alternating edge leading (EL) strokes from side to side, a burr fold over can occur and go unnoticed unless the edge is inspected optically after every stone in the progression.
One way around this is to sharpen EL and do only one side, stop remove any burr formed by cutting into felt or something else, and then do the other side and repeat.
For finishing your suggestion of EL and increasing the angle slightly is one way to go or else a small number of passes with edge trailing when the stage of alternating side to side passes has been reached. As you so rightly say, the challenge is knowing when to stop.
Again in my experience, stones will always generate some burr and its complete removal requires stropping. Here the question becomes whether the additional time spent stropping can be justified in terms of the envisaged use.
Cheers
John
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Have you tried metal-polish on hanging denim strop?
If tried and rejected: why?
Chris
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Hi Chris,
“Have you tried metal-polish on hanging denim strop?”
No, I strop my knives and woodworking tools on either leather or balsa loaded with diamond powder.
Cheers
John
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Hmmmmm… Good idea ! Balsa is a soft wood !!!
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Hi John,
Thank you very much for your insight.
I just bought a leather strop and some 1 micron aluminium oxide powder and tried it. I have to say that I haven’t got much success yet. Under my finger pads I felt that my knife was a little duller or maybe it was actually the true clean apex without a burr or a wire edge, I’m not sure. Guess I have to practice more, but as of now I may stick with stone-only sharpening method.
You last question made me rethink about my plan of buying an 8000-grit stone as I already have Naniwa Pro 3000. It’s really just to satisfy my curiousity about the differences of the edge finish and sharpness gain. Whether it’s worth the additional time and money spent or not, I would say that for me it might not.
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Hi Blggg,
Do you have access to a low power microscope, or at least a high power loupe? To my mind they are just about essential for determining whether a particular step in the sharpening process works or not.
In sharpening there are a lot of factors at play and sorting out what is going on can be quite a task.
Cheers
John
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Hi John,
As far as I know, no. I’ll keep practice and see the results.
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็Hi Todd,
Have you tried the jointing technique (grind the edge on the stone) and doing a few laps of edge leading or edge trailing? Wonder how the results under the microscope would be.
I have recently tried it pretty extensively and I found that most of the times I got a smoother and stronger edge. However, before jointing, I have to make sure that I have really reached the apex and probably created a little wire edge, so that when jointing, the edge isn’t too dull to bring back with a few laps of edge leading or edge trailing (I cheated the risk of using too much pressure when jointing by grinding the knife the side of the stone instead). The challenge is still knowing when to stop doing edge trailing before creating another burr or wire edge.
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Yes, I have been experimenting with cutting into the edge of a stone for quite a few years. I find it is much more effective than jointing and avoids any lateral forces. The downside is that does damage the stone, so I tend to use junk stones like the King 1k/6k or one of those naguras that often come with premium stones.
The important thing to know is that the amount of steel removed is quite small – it removes the burr and leave you with a uniformly rounded edge with a radius of 1-2 microns – easily micro-beveled from that point.
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I think I have missed something in your writing. Which is much more effective than jointing? Is it cutting into the edge of a stone? I thought cutting into the edge of a stone is similar to jointing.
After having done some more jointing, I have found that the results are not consistent (sometimes I get quite a sharp edge after a few edge leading or edge trailing strokes, sometimes I need to resharpen the knife to get the edge back to a sufficient level of sharpness). And I definitely have to put a micro bevel on to get the edge back to the sharpness I wanted. So in the end, I get a probably stronger and cleaner but less sharp edge. I suspect that the inconsistent results might be due to not producing enough foil edge. I think your simple-straight-razor-honing method might be the way for me to go as it produces a lot more consistent results and definitely sharper edge. However, I don’t have a denim strop, I only have a leather strop. Will a leather strop loaded with 1-2 microns aluminium oxide compound reduce a chance of not getting rid of a foil burr as you show in Simple Straight Razor Honing by stropping with 0.5 micron diamond compound?
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Speaking of traditional steels (not S110V) jointing and cutting into the edge of a fine stone (King 6k or Shapton 8k) remove far less steel than you might imagine. Lightly jointing (rubbing the edge on the surface ) just doesn’t remove enough steel to make the edge uniform and slightly blunted. You really need to make several visible cuts into the edge of the stone. See for example the last 3 images in what does steeling do? part 1
After cutting into the stone you would need to remove 1-2 microns from each bevel side to reach the apex if you stay at the same sharpening angle. This is too much for a very fine stone. However, if you increase the angle to microbevel, a very fine stone can easily remove enough steel to reach the apex. A honing rod also easily removes enough steel to reach the apex from this point. Stropping will not restore the apex from this level of dullness.
You can replace the denim strop with paper or cardboard, work the metal polish in with the spine or a screwdriver shank before using it on the blade edge.
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How negligent I am to have missed the test you have done. I should have read it long time ago, but I intentionally skipped as I didn’t steel knives. In that test, you cut the Olfa blade, which had an excellent edge into the stone (I really wish I could make an edge like that. Looks like the blade was finished with 0.5 or 0.25 micron strop). I suspect that if I draw out some foil edge, grinding the edge super lightly into the side of the stone might blunt the apex even less. But all in all, seems like if I want the cleanest edge as much as possible, micro convexing or micro bevelling couldn’t be avoided.
I might have missed some tests you did again. What is the difference between using paper or cardboard for strop vs leather? Will paper or cardboard minimize a burr better than leather? And I guess paper is uncompressible, whereas cardboard is compressible? Are majority of jeans made of denim? The labels of most of jeans that I have written 100% cotton. If they are denim, I might try stropping on some old jeans.
Really appreciate your comments.
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Paper or cardboard is a substitute for denim, not leather. The mechanism by which a strop can gently come over the edge and produce micro-convexity comes from the loose fibers on the surface, not the compressibility of the bulk substrate. So paper or cardboard (card stock) are ideal – I would avoid corrugated cardboard.
The denim I use is just strips from some old cotton Levis – a smooth cotton twill kitchen towel should also work. The key is that it has opening/depressions that can absorb the larger abrasive particles in the metal polish. It’s the same principle as to why we use a soft cloth to polish silverware, except the strop must not be stretchy.
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Ok, I will try a cardboard or denim. Do you normally using the same method (straight razor honing) to sharpen other types of knives (kitchen, fixed blade, folding, etc.)?
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Hi Todd
I have tried stropping my kitchen knives on pasted hanging denim and the results seem very good. The edge is very smooth when I touch it with my finger, but it can whittle some hair off my leg (not sure if rounded edge will also be able to whittle hair).
This is the first time I tried stropping on a hanging material. Although the result is very positive, I’m not sure what angle I should hold the knife at when stropping? I laid it quite flat to the denim but not totally flat, maybe like 3-5 degrees. If I strop with the same angle as I sharpen, will that round off the edge?
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