Hardening chisels

[John C Cox]

Heres the basic process and junk needed to harden and temper chisels.
Note: do this at your own risk. You will wreck some chisels. And you might catch yourself on fire... Don't say I didn't warn you.


The Stuff.
Oxy-mapp gas torch
file
magnet
cup full of olive oil (canola, soybean, and peanut oil also work well).
Fire extinguisher
gloves
vice grip



The flame



What it looks like with no flash in the dark when the magnet no longer sticks.
I would call this orange, but I am going by the magnet.



With flash - same as above but brightly lit. Nonmagnetic



Quench in oil. Up down up down.
Don't stir around or it may warp sideways.
test with a file - the file should skate on the hard end now.

Note: this is a cheap Harbor Freight chisel and wouldnt harden in oil....
See next pic for what happened when I hardened it in water...



This one was water quenched. Crackity crack. Wouldn't harden in oil.... .



Dont say I didn't warn you about warping.
Don't be greedy - only harden the first 1".




Temper in 400F oil for an hour or 2... I don't like chippy edges.



Next - re-establish a nice flat back and then sharpen.

These are much harder than straight out of the store...

[James Pallas]

Interesting and straightforward post John.
Thanks
Jim

[John C Cox]

Here's the chisel - untreated and after quench and temper.



The Buck Brothers chisel behaved beautifully. And they are available at the Local Home Depot.

Also oil hardens successfully:
Irwin/Maprles blue chip
Footprint 87 series blue handle

Would not oil harden:
Narex - water hardens well but warps.
A miscellaneous no-name German chisel - water hardens well but warps
Harbor freight wood chisels - cracks on quench in water. Temper goes soft at a fairly low temperature. Behaves as if it's some sort of low/medium carbon alloy...