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Thread: Flattening back of a mishandled chisel

  1. #1

    Flattening back of a mishandled chisel

    I've been working my way through a bunch of chisels that has been my grandfather's. They are all quality chisels that he used in his woodshop, but after he died, I guess others have been borrowing those chisels for other uses. My grandmother gave me those (and a lot of other tools) last year. They'd been lying around for 15 years since my grandfather died.

    I was flattening the back of a 3/4" chisel yesterday, when I noticed that there seemed to be a large bump on the back, and I wasn't flattening anything at all in the first half inch of the chisel!

    A bit of checking with a ruler confirmed my suspicion. It seems like a fine chisel has been used to open paint cans or something. It is slightly bent.

    How would you deal with this?

    I'm considering two options. One is to try bending it back (which I have some doubts about), and the other is to file the bump away.

    The bend is slight enough that filing some of it off wouldn't matter. But it would take hours of grinding on the water stones.
    Last edited by Staffan Hamala; 03-01-2011 at 1:59 AM.

  2. #2
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    If it is a very slight bend, it may be easiest to file it off. (Oops! I could erase this error, but everyone has already seen it. A file should have no effect on a good chisel. Abrasives on paper are the way to go. Sometimes even after a few cups of coffee my brain is still off playing in the snow.)

    I have seen a lot of light weight chisels with a bow in them. My impression is it may be from over enthusiastic whopping with a mallet.

    I think it would take a lot of paint can opening to bend a chisel.

    Maybe others will have more experience along this line.

    Another thought was to use a narrow piece of abrasive paper from a roll so the work can be confined to the section where it is needed.

    jtk
    Last edited by Jim Koepke; 03-01-2011 at 3:08 PM.
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  3. #3
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    you need a more coarse abrasive than waterstones.

    There are a lot of old chisels with a belly. If what you're seeing is the edge is proud of the spot you're lapping a fraction of a millimeter, it could just be "belly" from not lapping the back of the chisel properly when sharpening.

    If it is much more drastic than that, it's probably bent. If it's bent, hammer it back.

    If it's just belly, lap it out.

    If you have anything flat, you can spray-stick norton 3x in 80 or 100 grit to something and start there, it'll be miles faster than your waterstones. Running a big belly out on a medium grit waterstone is a form of personal disciplining.
    Unleaded tastes a little tangy, supreme is kinda sour, and diesel tastes pretty good.

  4. #4
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    Unless the chisel is entirely too soft to be a decent chisel,you will not be able to file it. As David said,get a more coarse abrasive.

  5. #5
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    Or just bend it back. Its steel, you can bend it back with no problems. Block up by the tang and at the cutting edge, and whack it. Beats grinding and a lot faster. The best chisels in the world are made by beating on them, so a whack or two on yours is not going to hurt anything.

  6. #6
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    I would be very careful about "wacking" a chisel. It may break. You can warm the chisel to about 350 degrees with out affecting the temper setting if it's good steel. I would warm it up to about 200 to 250 F, place it in a preopened metal vice, and just use hand pressure to correct the bend.

    The above is if the "bend" is more than slight. If it's slight, the recommendation to use a heavy abrasive is good. Use a 80 grit used sander belt on a good flat surface. No need to glue it down. Just work the "bend" area in a concentrated manner with finger pressure on the bump. Work it until it looks flat, then put the chisel bend to a fine grit ( like 320 ) and check for flatness. It may take several turns on the heavy sander belt to really get it flat. The use of finer grit sanding will point out the flatness after the heavier grit markings are removed. Once the 320 grit test looks good, go to a 800 grit water stone or a Xcoarse diamond and keep flattening. I also recommend you use the direction of the stroke on the sanding one way and then another to recognize when the grit of what ever grit you are working on has been completely removed.

    You'll probably have to do the above sanding even after the bend is adjusted back towards flat. Use a good straight edge to check your bending back to flat.

    Good luck and keep us posted.

  7. #7
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    I forgot to say,if the chisel is made of hardened steel(which it certainly MUST be to be a good tool),you will INSTANTLY break it in 2 by trying to bend it. Terry's post is valid,but the cold vise will nearly instantly draw out the heat. Be careful. I've straightened many a tool by this ethod,but you need to know what you are doing. Safest thing is to just grind it flat with coarse abrasive.

    I generally heat the tool to a light straw color and bend it. Light straw color tells you the tool is actually hot,and is below the temperature that will damage the tool. It is dangerous,though,and the vise will cool the tool very quickly-IF it is a metal jawed vise.
    Last edited by george wilson; 03-01-2011 at 11:51 AM.

  8. #8
    Thanks!

    The bend is indeed slight. I can't see it without having a ruler against the back.

    I will try with a coarse abrasive paper instead of a file.

  9. #9
    Quote Originally Posted by george wilson View Post
    Unless the chisel is entirely too soft to be a decent chisel,you will not be able to file it. As David said,get a more coarse abrasive.
    I'm intrigued. I thought the reason for not using a file would be that it is too coarse. How come abrasive paper would work when a file would not? Is sand paper harder than a file?

  10. #10
    Quote Originally Posted by David Weaver View Post
    There are a lot of old chisels with a belly. If what you're seeing is the edge is proud of the spot you're lapping a fraction of a millimeter, it could just be "belly" from not lapping the back of the chisel properly when sharpening.
    I think you're right. I've checked more closely now, and it's exactly as you describe. I also saw that the corners are a fraction lower (more off) than the middle of the cutting edge.

    Quote Originally Posted by David Weaver View Post
    Running a big belly out on a medium grit waterstone is a form of personal disciplining.
    That would be like a four hour meditation or something. :-)

  11. #11
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    People have different theories on this, on about how much of the chisel needs to be flat.

    I remember david charlesworth driving himself nuts with a bellied chisel, I think he worked it on a king stone. and he wants the entire back to be in one plane so he can lay the edge of the chisel over a stone and make it ever so slightly hollow. Blech to that process with a king stone.

    I have seen Chris Schwartz make a similar comment about a chisel or a plane blade or something, about how it's false economy. To that, I'd say false that it's false economy, at least if you use the right stuff to get something old back into workable shape. I have not seen a chisel that I can't grind the edge of the back into shape in 15 minutes (i have a holder that holds chisels, though, and use coarse diamonds). The absolute worst iron I have ever refurbed was one that should've been thrown away, pitted such that I removed half of the depth of the hard steel lamination (it was an old woody iron) - it took 45 minutes to do that, and it was a big iron.

    Anyway, here's my theory - the last inch or so of the chisel (or even less) is what does the work in a cut, and if you like to use guide blocks, it references the guide block close to the cut. If the back side of this chisel isn't going against a depth guide far out from the cut, or something of that sort, I would worry about the edge and the first inch in. Once you get that lapped into a flat plane such that you can polish it on a stone and do the same thing again (and again+) when you need to resharpen, you're good. It'll still take some work and it's better done on something other than a waterstone, but you won't needlessly try to flatten 4 inches of blade on the chisel to make it look like a new one.
    Unleaded tastes a little tangy, supreme is kinda sour, and diesel tastes pretty good.

  12. #12
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    Files are not hard at all. They may be heavy, and you can temper them and make tools from them (ie drawknifes, etc...I wouldn't, but you could) but they are very soft. I would say that the abrasives on paper are harder, but I may be wrong. There is a difference between what an abrasive does and what a file does.

    If your striking tools or plane irons are anywhere near as hard as they should be, your file should will just glide across with minimal result. On an axe or a drawkife you would be able to use a file.

    Quote Originally Posted by Staffan Hamala View Post
    I'm intrigued. I thought the reason for not using a file would be that it is too coarse. How come abrasive paper would work when a file would not? Is sand paper harder than a file?

  13. #13
    Ok. Thanks. You learn something new every day. :-)
    I thought I had found a new use for a file, but was proved wrong. :-)

    I've got some 60 grit abrasive paper that I will try using tonight.

    /S

    Quote Originally Posted by john brenton View Post
    Files are not hard at all. They may be heavy, and you can temper them and make tools from them (ie drawknifes, etc...I wouldn't, but you could) but they are very soft. I would say that the abrasives on paper are harder, but I may be wrong. There is a difference between what an abrasive does and what a file does.

    If your striking tools or plane irons are anywhere near as hard as they should be, your file should will just glide across with minimal result. On an axe or a drawkife you would be able to use a file.

  14. #14
    Thanks. That makes sense. No reason to work more than necessary. :-)

  15. #15
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    Of course abrasives are harder than a file!!!!1 You must remember that abrasives of different sorts are used to grind hardened steel precision parts,and stuff like planer blades,etc. Even gem stones are ground with harder abrasives.

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