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  1. #1
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    Default Method Proposed to Improve Chisel Edge Retention and Resistance

    I've been experimenting for a little while with chisel edges, but just off and on. The issue for chisels in general is that edge failure usually comes by chipping or bending, not due to wear. Increasing the angle enough to eliminate it entirely makes a chisel that presents a lot of wedging force and will feel blunt, even though it won't take damage.

    Out of laziness sharpening some other things (incannel gouges, especially, and really thin knives), I've come to find out that I can get both of those things to be sharper feeling and more durable than I could by hand, but the challenge with regular chisels was to maintain their geometry and not have them feel more blunt / dull.

    The method is this:
    * primary grind - 19 or 20 degrees
    * secondary bevel - with a medium stone (1000 waterstone or similar diamond stone) - 25 degrees
    * then a buffer with a stitched cotton (sisal?) wheel using a relatively coarse honing compound of about 5 micron aluminum oxide buffing only the very tip of the chisel (not heavily buffing anything, just rounding over the last little tip). This 5 micron number is a bit misleading. I've found that good 5 micron buffing stick does less scratching in a buffing wheel than does 1 micron on a flat surface. The resulting edge doesn't show scratches large enough to allow visible light in them, thus a finer buffing stick isn't necessary (and may be slower)

    The theory is this - edge resistance in cutting is a combination of wedging forces and severing. We've always heard that if we don't have two meeting planes, the edge will be less than ideal, but the last little bit of the plane is what fails and failure begets more failure, etc. It extends the next sharpening time and marks up work, and points us toward trying to find only ideal chisels (thus the notion that sorby chisels are too soft and some overhardened japanese chisels are too hard).

    In order to improve edge performance, I want to round the very edge (without being anal retentive about knowing angles, etc about the round over) and make up for the rounding by decreasing the angles behind the edge and by improving the polish of the edge.

    Keep in mind, this isn't a hair brained idea that I thought up first and just wanted to work, it's something I ran into by use and then have measured what works at the request of someone else here in the states (two someone elses, actually).

    What I've found is that suddenly, the very soft sorby chisels are usable (more than usable) and will work for a very long time in between sharpenings. If they are just plainly sharpened at 28 degrees on a hollow grind, they fall apart quickly. The buffed edge above also gets through the cut more easily than a "perfect" 1 micron diamond honed 28 degree bevel. Increasing the angle until the edge holds up would do the job, but the cut resistance on the flat bevel is already greater than the cobble mentioned above, so what's the point there?

    This sharpening method allows for brisk bevel side secondary bevel refreshing (necessary) and touch up with the buffer in about 30 seconds total. One stone, one buffer - no need to address the wire edge, the buffer removes it.

    I made a video (but it's very long and I won't post it here - it discusses all of these aspects), and tested two edges on sorby chisels and here's what resulted:
    * the cobble method mentioned above got through beech more easily and looked like this when done: https://i.imgur.com/Oi9obaS.jpg
    * a 28 degree edge was very sharp, but after chopping the equivalent of two half blinds of waste in beech, looked like this: https://i.imgur.com/N71EKxf.jpg

    The second edge is deflecting as a softer chisel will. The deflection is about 2-3 thousandths of an inch. From what I can gather, the buffed area on the end of the first chisel is somewhere between 5 thousandths and a hundredth long (the damage is occurring within the modified area with the new method - but not on the modified chisel).

    https://i.imgur.com/tN4PfxO.jpg

    This is the look of the end of a sorby chisel (ignore what looks like two primaries - and notice the secondary bevel that's about a quarter of the bevel width is after several sharpenings and it's ready for a trip back to the grinder)

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  3. #2
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    Q&A from what I've heard so far in the states:
    Q: good for plane irons then, too, right?
    A: I don't think it's as promising. Clearance is important, and plane irons generally wear off rather than take impact damage. There's no need to address the back of a chisel in normal use, but we have to address the back of the plane iron every time we sharpen, so there may be no gain in time, either.

    Q: what's the buffer, wheel and compound
    A: HF buffer here, typically on sale for about $39 US, 6 inches, 4 amps, 3600 rpm - not really that important, but the speed is nice. Wheel is an 8 stitch 6 inch wheel (which seems to be ideal in terms of backbone - you need some, but too much, like hard felt, and the wheel becomes aggressive and works too fast and can draw a wire edge). Compound is an inexpensive 5 micron jackson lea brand calcined alumina (I think, it just needs to be something other than outright junk, could be a different US made brand). The cost of this compound in the states in a stick is $11 for 3 pounds. Compare to most honing sticks marketed to woodworkers,which are generally that price for 4 or 6 ounces or so. yuck.

    Q: what's the point? It's the same as the sellers method.
    A: the sellers method generally results in more cut resistance and significant time (if done properly) on the preliminary diamond hones to prevent bevel angle creep. This is instead intentionally keeping the entire edge more shallow than a chisel would tolerate and rounding over only a tiny tiny stripe. The point is to address difficult wood without having to buy either expensive chisels (actually to outperform them at the same time vs. a traditional flat microbevel or full hollow ground bevel) , or make significant adjustments day to day for one type of wood vs. another.

    Q: won't this just make a more blunt chisel?
    A: no, the thinness of the edge makes up for the tiny rounding. There's still plenty of sharpness to sever anything. If experimenting with this and finding that the chisel isn't as durable or easier through a cut (as in, 6 mallet strikes through a sample piece of wood where 3 or 4 more degrees of flat bevel vs. the secondary bevel results in 8), then keep going until both durability and less effort is achieved. It should be noticeable

    This improves durability somewhat, but it doesn't allow you to turn chisels into a crowbar. Significant bending and prying will just damage the edge beyond the modified area.

    Q: why not just use the buffer only
    A: control of geometry is important to get both benefits from the method. continued buffing without resetting geometry is going to yield edges too shallow or too steep and too much roundover(more cut resistance).

    https://i.imgur.com/OgtFRzJ.mp4
    Q: (from the video), why touch the back of the chisel on the side of the buffing wheel
    A: to remove the wire edge if there is any. The corner of the wheel has no backbone and won't really hone anything off. It replaces a strop

    Q: Now you need a buffer -the process is more complicated
    A: it now takes 30 seconds to resharpen a dull chisel. Add another minute once every 4 or 5 sharpenings to regrind, keep account of how much less often sharpening is needed. one stone and the buffer replaces two stones and a strop. It seems less complicated and skillful and gets better results faster

    Q: can this be done without a buffer?
    A: yes- probably the easiest way to do it is corian or wood and 1 micron diamonds, lifting (rolling, not just a flat facet) the final angle about 8-10 degrees past

    q: how big is the performance difference if done right:
    A: a modified sorby chisel performs better in practice than one with a flat facet, even if the flat facet chisel is far better quality (I'd venture to guess I could more than close the gap between the worst and best chisels in most tests). I recently made a case and pared off the tenon shoulders with a harbor freight chisel equivalent to the $8 aldi *set* of chisels. Its slightly softer than sorby's chisels (the lowest in rob streeper's tests), but worked very well in cherry. That includes paring the bead miters on the doors without anything other than a very smooth cut.

    Q: can't I just do a three bevel system and a tiny flat microbevel with a honing guide?
    A: I guess. It doesn't seem to be quite as durable, though. If an edge is failing, a tiny microbevel at 32 or something degrees after a 25 degree secondary will be better than increasing the angle to 28 or 30, so it's better than nothing


    I originally did all of this on chisels that didn't hold up that well rolling similar to the A: to the last question to find that most really hard chisels or nasty woods suddenly were tamed without adding much cut resistance. After experimenting with knives, I realized that I could probably ease the angles behind the edge once it no longer failed (a superb vegetable knife will have a very thin grind and have the edge modified as discussed here and seemingly never damage.

    For the knife enthusiasts, this pretty much equalizes the differences between an inexpensive 61 hardness japanese knife of stainless (like VG10) and the really expensive knives. The key is only to modify as much of the edge as is needed to prevent failure. To do any more creates more work.

  4. #3
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    What's this method going to be called?

    * The unicorn bevel or unicorn grind.

    Someone on an american forum started calling it "the weaver grind".

    I hate that. It's my objective making planes and posting videos about that, or coming up with stuff like this, to make for unbranded things that "gurus" can't attach their names to, but that we can share. I'm sure that this has been done elsewhere, but I've never seen it specified properly to achieve what's equivalent to chasing unicorns...

    ...a sharper (perceived from cutting quality and resistance) edge from cheap tools that holds up better, leads to sharpening faster and doesn't require some branded overpriced junk

    When I was buying, grading and selling used japanese natural stones, I was one-upping the sellers of $800 newly mined stones that often don't outperform something picked by an antique puller in japan for about $80. But sometimes I would run across knife people who were looking for unicorns ("i want a chisel that leaves the jigane super matte with no scratches but the hagane very bright and super sharp, and that cuts really fast"). My answer was that "I can run through my stones and find you something as close to that as possible that will match or better anything you'll see new for $800 and for about $150.....but I don't have a stable full of unicorns, so we're bound by reality".

    The buyers were usually really happy once they got their stones. One guy bought 5 stones from me, then bought 4 stones from a dealer here that cost $400 or more, spending about $5000 total and sent me a message later that they weren't as good as the stones I sold him. Even after I graded stones and told him I'd been through a few hundred so my advice was probably reliable, he still went looking for someone else who offered unicorns. But the guy just sold horses with narrow dunce caps instead.

  5. #4
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    This sounds like a little bit of nothing in terms of what's being discussed here, but I just mortised a jack plane body yesterday in indian rosewood using the sorby chisels (same ones that R. Streeper found almost unusable in hardwood).

    As someone else has latched on to this in the states and has taking more numerous pictures (and may blog on it), I don't write blogs - who would read it?

    At the request of someone here, though, I took a picture of the two edge profiles from the side, which might be instructive.
    The first picture is a 28 degree flat bevel attempt (ended up being closer to 27), but I'm not regular guide user so that's probably close for me. The second shows the secondary bevel mentioned above, right off of a grind - the pictures are close up (you can see by the scale) so the primary bevel is way off of the picture - it's about 20 degrees or so. The secondary angle is 23 (apparently, I was guessing 25 - the third or 4th refresh, that might occur), and you can see the length of the roundover - mostly due to the buffer, a tiny contribution due to the imperfection of hand honing.

    The finish on the side of the chisel is not from the buffer - I had to clean up the manufacturer's grinding accuracy with a washita stone to get a good picture. Those scratches are similar to what you'd see from a king 8000 grit stone, maybe ever so slightly coarser.

    flat bevel:
    https://i.imgur.com/giOQM06.jpg
    https://i.imgur.com/N71EKxf.jpg (This is the damage occurred at identical manification, so you can guess how far it would've gone into this edge - approximately 2 dovetail socket's worth of beech chopping)
    "unicorn edge"
    https://i.imgur.com/wyoqb4H.jpg
    (note the picture above showed very little or no damage, though I hadn't ever fully prepared the back of the chisel and it had some relatively coarse scratches)

    The significantly greater beating of mortising a full sized jack plane body in rosewood today would've left visible damage.

    I do all kinds of crackpot experiments, and get way in the weeds on things (like trying to build a near perfect double iron wooden plane), but this method is easy, cheap, and shows a whole lot of promise for chiseling.

    The very tip of the edge shows why it's not that great for planing with a standard angle plane, though (clearance at the very tip becomes limited).

    This is the level of polish done by the buffer (5 micron calcined alumina stick, which is *very cheap*, $4 per pound). I don't know if one could use an $11 3 pound stick in a lifetime. The buffer wheel is $7 and has indefinite life and never needs to be cleaned (this one literally sits below a grinder - it seems to be immune from contamination - I think anything that settles on it flies off once it's running).

    https://i.imgur.com/nW8rn6w.jpg

    Most of the grossness on the picture is wax or oil. This is a finer finish than the finest 0.5 micron sharpening stones (shapton 30k or suehiro gokumyo).

  6. #5
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    I did just a bit more testing to confirm that the results above hold true when switching the edge type back and forth on the chisels (verifying that none of the failure of the flat bevel was due to one chisel being better than the other).

    This time, I used apple for a specific reason - I have an offcut just under 3/4ths inch wide, which means I can use the sorby chisels to cut it without holding wood on the side.


    First test, same chisels (unicorn 1 inch, 28 degree 3/4ths inch) using the edges shown in the angle pictures (not resharpened, etc). flat bevel is 1 micron diamond, unicorn is yellow stuff.


    83 strikes to get the flat bevel chisel through the apple, 60 to get the unicorn chisel through the apple:


    edge damage to the flat bevel - 3/4 inch sorby:



    This apple feels a little bit harder and drier if that makes sense vs. the beech billet. The edge failure is much more uniform in it. If you check this chisel with your finger, it feels like a wire edge has been raised (a small one, but you can easily feel it.)


    1 inch chisel - unicorn edge. No visible damage. It's hard not to tap the mallet more lightly even from the start as it gets through the wood much more easily.





    Next, swap the chisels, unicorn the 3/4th chisel and flat bevel on the 1 inch chisel to make sure it's not the chisels and lack of consistency. (i've never perceived much variance in three sets of these chisels, but you have to check and make sure it's not also related to a bigger chisel transferring more of the mallet energy).


    80 strikes with the flat bevel, 55 with the unicorn. I paid a little bit more attention to not let off of the striking pressure since the unicorn was getting through the wood more easily.


    28 degree bevel, 1 inch chisel:



    Then, the 3/4th inch chisel unicorned:



    I'm not sure if any of that is minor edge damage.


    I drew 10 sections in each inch of malleting here. Again, wood narrower than the chisel width so no holding wood.

  7. #6
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    So I finally got around to trying this out. I think it goes without saying that it won't fix poor quality chisels.. It didn't help my Aldi chisels... But nothing does, so I'm officially giving up on them. It does seem to make the edges much more well behaved on the decent ones, vs jig sharpening.... So that's progress.

    I decided the part in the video about touching the back of the chisel against the corner of the buffer was unnecessary. Buffing leaves a little lump of waxy residue along the back of the bevel that wipes off on a paper towel or your pants leg, but it's not a wire edge. It's more likely that I damage something, buffing the backs, so I'm not going to do it.

    Overall, I'm provisionally calling this a win.

  8. #7
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    interesting that your aldi chisels are beyond hope. I thought sellers' comments about their edge holding was odd until I saw that WBW tested them at 62 hardness or so. I have the same chisels from before aldi carried them (at the risk that I already typed this in this thread here and not somewhere else) and they're about 58, I'd guess - similar to sorby. I thought for a while they may be softer, but I think they're just thinner. When you get to the mid 50s, chisels are unusable.

    The aldi and sorby chisels at 58 are unsuitable for anything but softwoods when sharpened to an apex, but hold up well "unicorned".

    I guess it more or less widens the range but doesn't solve everything.

  9. #8
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    I think you're right about occasional use and soft woods. I got a set of Aldi's for my Dad. I fully prepped and sharpened them, and he loves them. But he only uses them on balsa, spruce, and stuff like that, building model airplanes (which isn't chisel heavy anyway.) He's had them probably two years now and hasn't needed to resharpen them. So, that's perfect. He has no need for Veritas, Ashley Iles, or pre-1881 Marples...

    My issue is: I've got cheapish chisels that work well. I've got good chisels that work well too.... So I've got no good reason to keep chasing tools that don't. My Aldi chisels left the chisel drawer and now live in The Box of Shame.

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