Folks: what is the general consensus about trying to harden the edge of mid-size bladed (say 1/8 inch wide, 4 inches long) with a regular plummer's torch? Some of these torches develop more heat than others, but would it be a waste even trying? (Before I purchase one for the purpose.) The steels will be 10660-1095, 5160, and O-1. Thanks!

Can't be done in open air with one plumber's torch.

In a small enough enclosure you should have an easy time at it. It's easy to build a bean can forge with a propane plumbers torch. You need about 1 linear foot of ceramic wool insulation and a metal coffee can or large bean can. For heat treat you don't need anything close to welding heat, so propane should be fine from that small of a torch. you can switch out to mapp if you have problems of not enough heat.

Phil

Not a bladesmith but I doubt you could harden one properly with an o/a rig let alone a plumbers rig.
Ken

Of course hardening blades with an O-A rig has been pretty standard for stock removal bladesmiths for over 50 years now that I know of for steels with simple heat treat requirements---like O1.

Oxy-acetylene torches are great for some sorts of heat treatment work. The intense heat lets you really control things. The drawback is that as far as heating methods go, it's expensive.

I've never even thought to use a plumber's torch to harden anything but often use one for drawing a temper on small pieces when I don't feel like dragging out the larger torches.

Just today I was re-doing a few short chisels with parker taper shanks on them. The torch allowed me to re-treat the working ends without putting any heat into the shanks; it also let me handle the work with bare hands.

hardening occurs in the quench....take it to criticle(non magnetic) then quench in your medium (oil, water, etc) then use the torch...torch is fine as long as you can see the colors...a torch wont get it to non magnetic either....another alternative would be to bake it in a little oven....i got an oven for 5 bucks at a yard sale....but i have tempered quite a few with propane torch...i just did a bunch of chisels for a mason heated them up staightened them and ground an edge on them then i heated up to nonmag....quenched in oil(hardened) then i took a propane torch and hit them for a bit till i got a staw color on the edge..

a method that i have used for blades is one that i witnessed at an abana conference in seattle. two short pieces of thick bar stock welded to the jaws of a set of tongs perpendicular to the length were heated to yellow then clamped onto the blade opposite the cutting edge. the heat transfer runs the colors down onto the edge and when enough is enough (or just before) you simply let go. like anything this process takes practice but i think it is worth a shot. of course different strokes for different projects. i am always looking for new or better ways. let me know if you have any success and with what type of steel.

That is "tempering" using tempering tongs rather than hardening. It's a good way to do a differential temper and even works with double edged blades if your heating bars have a indentation to cradle the central ridge.