> I can get the steel strip, I can bend it to the shape I want - how do I
> heat treat it?
Best thing is to get a 1950s textbook for either school metalwork
lessons, or else a better handbook for engineering apprentices. In the
1950s, pretty much everything possible was still at the level where it
could be understood by the DIY worker, and most of it could still be
done over the kitchen sink. It's a useful generation for practical
textbooks (unless they have numbers in, in which case you want a
metric / SI one).
Then fins the right piece of steel. You just can't heat treat most
steel, it needs to have an adequate carbon content before it will
respond. So forget random bits of steel, forget new mild steel,
forget case hardening. What you need is old leafspring, so find a van
or truck scrappie. Don't use coilsprings, those alloys are really
awkward to handle.
The usual process is to harden (make it too hard, pretty much as hard
as you can), then temper it (soften it in a more controlled manner, to
You harden by heating and rapid cooling. Heating is a big gas
blowtorch, or a coal fire (charcoal won't have the heat, unless blown)
and then a quench by a rapid dunk into oil (old engine oil) or maybe
water (not IMHO, unless I'm making edged tools). Leave it in the
quench tank until cold enough to handle. BTW - oil may well ignite on
quenching, so use a big fireproof tank and have a lid ready to shut
over it and just leave it to its own devices. My tank is a big ammo
box. Heat until it reaches its Curie point - when a magnet on a bit
of coathanger wire stops being attracted to it - or just a bright red
is close enough for jazz. It needs to be hot throughout (at least on
the hard bits), but doesn't need to soak very long at this
Quenching involves polishing the surface up afterwards, then gently
heating from the middle (softer) part of your tool and watching the
temper colours travel towards the brittle edges. When the right colour
gets there, then quench again (probably in water). The colour you want
is up to you and your uses - but blue or purple is about right for a
Afterwards, test before use. Also don't trust the thing (until you're
good at making them) and expect bits to chip and fly off. You really
do want eye protection here!
It's cheap to buy leafsprings, once you've found them. So get several
and make a number of tools. You'll break some to start with.
Otherwise (both better and simpler) is to have a blacksmith make it
for you, to order. Best of all is to apprentice to a smith for an
afternoon and make it yourself, under their supervision.
There are also a number of US cutlery books like "$50 knife shop" that
are cheap and useful.