Burr Removal – part 1

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.

Sh16k_plus20back_01

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.

Sh16k_plus20back_02

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.

GNV_16k_HdenMM_03

Edge-on view of the blade following stropping on a hanging denim strop loaded with Mother’s mag polish (aluminum oxide).

GNV_16k_HdenMM_01

Edge-on view of the blade following stropping on a hanging denim strop loaded with Mother’s mag polish (aluminum oxide).

GNV_16k_HdenMM_04

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.

GNV_16k_HdenMM_07

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.

GNV_16k_HighAP_EF_12

Edge-on view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate.

GNV_16k_HighAP_EF_13

Edge-on view of the blade following 3 minimum force passes on the DMT EF (1200 grit) diamond plate.

GNV_16k_HighAP_EF_15

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).

GNV_16k_HighAP_EF_17

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.

GNV_16k_HighAP_EF_19

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.

GNV_16k_HighAP_EF_21

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).

ZDP_EF_EL_01

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.

ZDP_EF_EL_p25PD_hRoo_01

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.

ZDP_EF_EL_p25PD_hRoo_03

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.

ZDP_EF_ET_01

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.

ZDP_EF_ET_wood_02

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.

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40 responses to “Burr Removal – part 1

  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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  2. 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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      • 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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  3. 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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      • 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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  4. 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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  5. 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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  6. 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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  7. 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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  8. 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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  9. 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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  10. 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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    • 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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  11. 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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  12. 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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  13. 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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  14. 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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