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Thread: Japanese chisel

  1. #1

    Japanese chisel

    I have four nice Japanese chisels that I’ve had for several years but haven’t used much. I decided to dust them off and sharpen them up. I’m sharpening at 35 degrees and three sharpened up nicely. The 1/2 inch chisel though keeps fracturing along the edge ruining the edge. What is the recommended angle on this type of chisel?

  2. #2
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    Sometimes it's not the angle of sharpening, it's that the steel has issues up front. Might have to get past the first 2-3mm to get back to good steel, just make sure that you have a solid line of steel across the back, and that you're not getting into the hollow.

  3. #3
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    What sort of fracturing? Entire edge folding over at once? Some chipping? Entire edge chipping? Becoming ragged? Out of curiosity what type of chisel is it and what tasks cause the fracturing? The more tools I make the more I realize that "sharpening past stuff" may just be a woodworkers saying thing. I suspect this advice arose from hobbyist heat treating with a torch and overheating the tip of tools if they have pre-ground a bevel or concentrate the heat in the tip area. Decarb or picking up carbon from the coke or charcoal fire is slow and not too serious at the temperatures/time needed for heat treating and the thin thin thin layer of whatever is off is easily removed when the tool is first given a courtesy tuning and should be gone; certainly gone by the time you've flattening the back and sharpened up a couple times. Unless the smith forgot it in the fire.

    No knife maker goes and grinds past "stuff" on their edges before final grinding the bevels or expect there to be people grinding out 2-3 mm of steel and then spending weeks thinning out the blade to match original specs. Nevertheless hone away, can't really hurt.

    Is the back flat? If the wire edge is not removed entirely then fracture like stuff happens instantly. A tool back out of flat or plane can interfere with burr removal.

    35 is plenty steep for pretty much anything.

    At some point you might find perhaps the chisel is just a dud. Perhaps the smith left it overheating, perhaps it was over tempered, under tempered. The latter can be fixed carefully but requires you to know that these particular fractures are symptomatic of an under tempered chisel. If the symptoms are of a brittle kind and retempering doesn't work and the symptoms continue then it is a problem of the grain size being too large; overheated in before the quench.

  4. #4

    Attached photos

    Thanks for the replies. The attached photos show the chisel and the fracturing as best I can capture it with an iPhone.
    IMG_0793.jpgIMG_0789.jpgIMG_0788.jpg

  5. #5
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    Actually sharpening past a burned factory edge is definitely a thing with knife people. Knives are usually factory sharpened with a belt sander and buffing wheel, and it is difficult to power sharpen without overheating the steel at the very edge. The affected area is much less than 2mm though.

    That may or may not apply to this Japanese chisel, but the first thing to try would be to just sharpen it several times and see what happens. It would not be the first tool whose properties improved over time with repeated sharpening. If no improvement, then you can try retempering (will have to look up appropriate temperature). I think in Odate's book he mentions leaving a too-brittle blade up on a tin roof for a day, which would be the same idea.

    And yeah, 35 degrees is as steep as I'd ever want to go for a bench chisel. Ideally they can be sharpened at 30 degrees and hold up. A chisel that needs to be at more than 35 degrees to hold its edge is not that useful.

  6. #6
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    Quote Originally Posted by Robert Hazelwood View Post
    Actually sharpening past a burned factory edge is definitely a thing with knife people. Knives are usually factory sharpened with a belt sander and buffing wheel, and it is difficult to power sharpen without overheating the steel at the very edge. The affected area is much less than 2mm though.

    That may or may not apply to this Japanese chisel, but the first thing to try would be to just sharpen it several times and see what happens. It would not be the first tool whose properties improved over time with repeated sharpening. If no improvement, then you can try retempering (will have to look up appropriate temperature). I think in Odate's book he mentions leaving a too-brittle blade up on a tin roof for a day, which would be the same idea.

    And yeah, 35 degrees is as steep as I'd ever want to go for a bench chisel. Ideally they can be sharpened at 30 degrees and hold up. A chisel that needs to be at more than 35 degrees to hold its edge is not that useful.
    Robert, I forgot about factory knifes. Big miss. There was quite a lot of turmoil when some Bark River or some other smaller "better maker" was found to not take the steps to prevent overheat. And yes much less than 2mm unless the worker is having a seriously bad day. But the individual knife-maker are far more careful... At least from what I see and what I hear from discussion on knife forums. Water-cooled belts are common now, and VFD allows for snail like paces. Also I still think that knife makers with good HT don't expect people to hone away decarb. People certainly don't expect to sharpen past more than the microns of belt burned steel.

    Rick, I can't really tell the type of chipping from the pictures but it looks decently severe. The back looks like it could use a couple minutes of work. Not sure if its a shadow but the sides on the backside look more polished, not sure if this is dubbing going on or some concavity, perhaps affecting burr removal.
    Best of luck.

  7. #7
    Japanese laminated chisels/plane blades are usually tempered to a ridiculously hard rockwell (RC 65 or more, compared to a knife/western plane blade at about RC 60). I think their sharpening technique is delicate to avoid chipping this brittle hard edge... I had trouble sharpening my kanna blade without chipping occurring until I tried using diamond lapping films which did the trick. You could temper the chisel back some yourself. The kitchen oven works well for this, you could try 300 F first, then if still too chippy keep progressing towards 400 F. Note that my kitchen oven is actually 50 F hotter than the dial states, so be careful.
    Last edited by Allen Jordan; 10-26-2018 at 1:28 PM.

  8. #8
    Thanks for all the suggestions. I did flatten the back before I started the process, it just doesn't show real well in the photos. I could have done a better job of polishing the back of the blade so I'll start by making sure the back is nice and flat and well polished. I think I'll start with another round of sharpening working the edge back a millimeter or two and see if it is just a poorly tempered edge. If that doesn't work, I'll try tempering the blade although I find that a pretty intimidating option. I've read some articles on this and seen some youtube videos but my confidence for this is low.

  9. #9
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    If you need to retemper probably the safest way (in terms of not overdoing it) is in the oven. You should calibrate the oven with a decent thermometer first, the built in thermostat is notoriously inaccurate. My guess is that you want to shoot for around 300 degF to get something in the 63 Hrc range. If you fill a baking pan with some sand and cover the blade that will help maintain a consistent temperature.

  10. #10
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    Quote Originally Posted by Rick Floyd View Post
    Thanks for the replies. The attached photos show the chisel and the fracturing as best I can capture it with an iPhone.
    IMG_0793.jpgIMG_0789.jpgIMG_0788.jpg
    The very hard (often around RC65) cutting steel is always forged, resulting in a close grained molecular structure enabling an unbelievably sharp edge to be obtained.

    Like most good things in this world, there’s a downside and that is that the hard cutting edge is extremely brittle; much more so than a western chisel. If a Japanese chisel is used to lever out waste, it’s almost certain to result in a chipped edge which means extensive work at the sharpening bench to restore it. https://knowledge.axminster.co.uk/tr...panese-chisel/

  11. #11
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    Quote Originally Posted by Rick Floyd View Post
    I have four nice Japanese chisels that I’ve had for several years but haven’t used much. I decided to dust them off and sharpen them up. I’m sharpening at 35 degrees and three sharpened up nicely. The 1/2 inch chisel though keeps fracturing along the edge ruining the edge. What is the recommended angle on this type of chisel?
    Hi Rick

    Looking at the photo, it is evident that the edge is brittle (which is not uncommon when a blade is new and perhaps slightly overheated in that area). Further, you should not need to hone a 1/2" bench chisel at 35 degrees. That is for the likes of mortice chisels, which are not expected to pare away thin slivers of wood. Your bench chisel should be honed at around 30 degrees. That is pretty standard for these chisels.

    If the chisel was mine, I would remove about 1mm from the end, and create a new primary bevel. The best way to do this is up to you, but a honing guide makes sense to me in this situation. Take the new face up to around 8000 grit. If this does not work, then remove another 1mm, and start again. I might even use a Tormek grinder and create a hollow grind at 30 degrees. In my experience, this does not place the edge at risk. I have done this for a few decades without chipping an edge.

    Regards from Perth

    Derek

  12. #12
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    Surface finish looks coarse and straight, I think it needs a few sharpenings and a finer finish. Steel fractures at the serrated tips first.

    Dont temper it without significant evidence to suggest that the chisel is the culprit and not your technique. Make certain that you are not using a prying action in any of your work.
    Bumbling forward into the unknown.

  13. #13
    Hey OP,

    How are you sharpening?

  14. #14
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    Chisel compromise

    Quote Originally Posted by Stewie Simpson View Post
    The very hard (often around RC65) cutting steel is always forged, resulting in a close grained molecular structure enabling an unbelievably sharp edge to be obtained.

    Like most good things in this world, there’s a downside and that is that the hard cutting edge is extremely brittle; much more so than a western chisel. If a Japanese chisel is used to lever out waste, it’s almost certain to result in a chipped edge which means extensive work at the sharpening bench to restore it. https://knowledge.axminster.co.uk/tr...panese-chisel/
    Here in my country there is a lot of very hard woods - actually a number of them figure amongst the world top ten hardest woods and they kill any brittle chisels.

    I am not a frequent user for chisels as most of my stuff are machine made, but I use japonese chisels only for paring such hard woods or chop and paring soft woods like pine. When chopping hard woods I prefer my construction grade Britain made Stanley FatMax, not stellar sharp but will support the abuse...

    All the best,
    Last edited by Osvaldo Cristo; 10-30-2018 at 6:06 PM.

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