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.

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

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.

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.

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.

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.

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.

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.

Quote:

---

Originally Posted by george wilson

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?

Quote:

---

Originally Posted by David Weaver

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

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. :-)

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.

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

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?

---

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

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.

---

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

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.

I use a belt sander with 80 grit on it for this kind of thing. Get's the bumps out fast. I wrote metal inside the belt so I wouldn't use it on anything else.

Quote:

---

Originally Posted by Staffan Hamala

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

---

(....he said on the neanderthal forum....)

I'm just saying.......;)

IMO, lots of these older chisels we come across were manufactured with an ever so slight belly. Not sure what the exact reason is but may have something to do with getting a bit more handle clearance in certain situations. Maybe some are caused by improper honing of the back but it really seems odd to me that same brand chisels found at different locations have identical bends to their backs. It shouldn't be a huge belly but like has been stated it really is only the first inch or a bit more that needs to be flat.

Im by no means 100% sure they were designed this way but have come across enough of them that instills this theory.

I have a couple of Japanese paring chisels with significant bellies (1/32" on 1 & 1/16" on the 2nd). Being accustomed to Western (LN) chisels with reasonably flat backs, I asked the reputable vendor if this was common or a defect. The response was this is common for these chisels and the curve provided "steering control." Vendor could have been blowing me off but...just in case they weren't...think of all the "steering control" you have with your chisels and just flatten the tip! I don't really know what steering control means but the chisels work well enough and I quit worrying about the belly.

If the belly belongs there, why do they hollow grind the backs of the chisels? As I understand it, the only reason for doing that is to allow you to flatten and maintain the chisel in a reasonable amount of time given metal used for the back of the blade. If they wanted it curved, wouldn't it be simpler to not have a hollow ground there? I'm no Japanese chisel expert to be sure, but the explanation seems a little fishy. Maybe I'm missing something.

Anyhow, the most frustrating thing in the world to me is trying to pare with a chisel that isn't flat. I go over the same spot 15 times and miss. Then I lift the back just a tinny bit and miss again. Then I lift a little more and it digs in and takes off too much. When the back's flat, paring seems much simpler to me.

I had a wide chisel I bought at a junk shop, that had a bit of belly on the back - it was taking a bit too long to lap the back, so I went with a tip I think I read in Garrett Hack's book; I used a small grinding wheel, the kind you chuck in a drill. I used that to grind away a bit from the middle, keeping away from the cutting edge. Then lap a bit more, to see how things are looking, and grind a bit more. Back and forth for a while; I ended up with a very, very slight hollow grind that has since mostly disappeared after lapping the back briefly after sharpenings. I did this a long time ago; I have no idea if this is a good idea or not, and I've only done it a couple of times, when I had a situation where lapping was taking an obscene amount of time, even with course paper. But just thought I'd mention it.

Quote:

---

Originally Posted by John Coloccia

...Anyhow, the most frustrating thing in the world to me is trying to pare with a chisel that isn't flat. I go over the same spot 15 times and miss. Then I lift the back just a tinny bit and miss again. Then I lift a little more and it digs in and takes off too much. When the back's flat, paring seems much simpler to me.

---

You might want to try a bevel down approach.

Pam

The work is going slowly forward. The back is getting flatter, but I still have the two dips in the corners which I need to remove.

Just to get a bit of a change, I left the 3/4" chisel be for a while, and gave the same treatment to a 1/2" chisel. Which this one I concentrated on the first inch right from the beginning, and not more than an hour later, I had gone through 80, 180, 240 grit sandpaper and 800,1200 and 6000 grit water stones, and am really delighted with the result. I'll finish the 3/4 inch chisel in the next few days as well.

I tried to get a photo of the mirror polish of the 1/2" chisel but it's really difficult to get it to show on a photo.

I'm attaching a couple of photos anyhow. The finished chisel, the half finished one, and one photo of the both of them. Very interesting to note that one is so much shorter. I guess it was my grandfather's favorite! :-)

I finally gave up on trying to fix the corners, so I concentrated on getting the rest of the first inch flat.

Attachment 185227

I managed to get a good edge however. But I'm a bit annoyed that I didn't manage to fix the corners. I might give it another go later on, or I might just grind away the first 2-3 mm of the chisel. For now, I'll use it as it is.

Joshua, I tried something similar but I used a regular grinder instead. I held the chisel to side of the wheel at a VERY low angle and CAREFULLY ground a hollow in the back. You want to practice with a junker first. I probably would not practice with an old swedish Berg from my grandfather...