The Story of the Easy Chisel Rehab

I've tortured the poor folks on Instagram with this story, so I suppose I ought to also put it up here.

I got a sweet stash of tools from Jonas' dad when I was in Denmark. They all need some rehab, some more than others.

Sweet stash of tools. The chisel I'm working on is the third tool from the right..

I got the fretsaw cleaned up and re-handled, but that's not what this post is about. Part of this haul was a few smallish chisels. For some reason all the chisels I have in Spain that are ready for rehab are around 1" wide. I thought the small ones would be usefull, too. It so happened that a 3/8" Jernbolaget chisel was exactly what I thought I needed for the next step on my rocking chair, and I don't happen to have one in my chest. Let's get this one handled up and sharpened.

I had a nice offcut of wenge left over from a Roorkee chair build a long time ago, and figured it would be perfect for this. It turns out wenge easily splits, and a tiny crack opened up after I finished the handle and drove it home.

The crack wasn't too bad. I figured I'd stuff some hide glue in there and put some massive pressure on it with a C clamp.

C clamps provide a lot of pressure.

The next day I took it out of the clamp, and figured I was golden. It looked great. All that was required now was to lap the back (which was a mess), grind the primary bevel, and hone an edge.

I took some care with all of this, and was surprised how quickly it went. However, I wasn't too happy with the edge after doing my thumbnail test. I ground it again, and honed a new edge.

My thumbnail test failed again. For some reason, I didn't trust my thumbnail test. It didn't quite work like it should, but I did everything right to put a razor edge on it, so figured I was good.

After two whacks on the chisel into wood, I discovered something very wrong, indeed.

Something very wrong, indeed.

I didn't really pay attention to the color of the chisel before. I figured it was just patina from age. But, it now occurred to me that the black-ish color of the steel combined with the crusty black flakes was a sign that this chisel has been annealed in a fire at some point.

I was trying to use a chisel that had unhardened steel. I probably could have done just as well with a chisel made from lead.

Plenty of clues this chisel had lost it's temper.

I got some great encouragement and advice on Instagram, including from Larry Williams of Old Street Tools. I watched his YouTube video and thought I'd give it a try.

I twisted the chisel out of the handle as carefully as I could. I re-opened the crack I had repaired, and opened a second crack, but they weren't catastrophic to the handle. A couple of clamps and some hide glue took care of that.

I was able to repair the handle after removing it from the soft chisel.

I don't have a forge, but The Frau is out of town, so I figured I go for heat treating this chisel using only a MAPP torch and a pair of pliers. I wasn't able to get the whole chisel glowing orange, so I just focused on the last inch or so near the business end. Once I got the little iron pools coming up, I quenched in a small jar of sunflower oil, which was the least expensive oil we happened to have in the kitchen.

This is the chisel after quenching.

Now I got the toaster oven out, and fired it up to about 400 degrees Farenheit (210 Celsius or so), and baked it for an hour. This softens the steel up a bit so it isn't quite so brittle.

While that was cooking, I removed all the squeeze-out from the chisel handle, and added a chamfer to the hole which helps the chisel seat all the way. I forgot to do this last time.

I chamfered the hole to help the chisel seat flat.

When the chisel came out of the oven, I was surprised there was even more color on it than before.

Very colorful now.

This didn't bother me, as long as the edge would hold up.

Being a small chisel, it didn't take long to lap the back, grind a 25 degree bevel, and hone it to 30 degrees.

Frickin' perfect!

Holy carp! This certainly did the trick. This chisel feels and cuts wonderfully now.

It doesn't look like much, but it sure works well.

If I had a buffing wheel, I might try to buff the black off, but I don't. I might try to polish it up at some point, but I think the color on it near the bolster will always be there. I might just leave the black on it. I will for sure leave it there for now.

Lots of colors on the metal.

I suppose the moral of the story is not to give up. If you have a chisel that has somehow lost it's temper, depending on the steel that is used it could be easily hardened again. This also might make it possible if you need to do some serious grinding, such as if you make a new side escapement plane. You can use an old iron. Just anneal it by heating it up and letting it cool naturally. You can then easily grind it to a rough shape, then harden it again.

I'll not be afraid to do this again, it was easy. But, hopefully none of my other chisels are like this.