Hi Larry,
Leonid’s describing a very old-school technique. It works, and is
really quick…so long as you already know what you’re doing, or
have someone there to show you. (One of those tricks that’s best
passed along via apprenticeship, rather than books.)
(A) Brine is saltwater. Usually either sea water, or a saturated
salt solution. (as much salt as the H2O will hold.) It pulls heat out
of the steel faster than pure water will. This gets you a harder
edge…so long as it doesn’t shatter the steel. Old style simple
carbon steels can take the stress (most of the time) but modern tool
steels that’re designed to quench in Oil (slower cooling) will
shatter if you try to cool them that fast.
I make my punches slightly differently, but the gist of Leonid’s
technique is as follows:
Heat the whole punch up to red hot. Some folks focus on the inch or
two on the working (shaped) end, and just get that hot.
This will also heat the rear of the punch as well.
When you hit red hot, stick just the shaped end (plus an inch or so
of shaft) into water, and swirl it around for a second or two, then
pull it back out.
Very quickly scrub the end with emery before the residual heat in
the other end of the shaft causes the shaped end to re-heat and fry
your fingers.
To properly heat-treat steel, you need to harden it (get it above
the critical temp (usu. red hot)), and then quench it off in
something. (usu. Oil these days.) That leaves it very hard, but very
brittle. To reduce the brittleness, you need to temper it. You do
this by controlled re-heating of the hardened area. Once the hardened
area gets to the right temperature, you quench it again. The "proper"
temp depends on what you want the tool to do. Engraving tools and
files are only tempered back a very little bit, but hammers and
springs are tempered back to nearly soft. Convienently, the
temperature can be roughly measured by looking at the color of the
oxide rainbow on bare steel. A very faint straw color is the first
hint of heat, which is where you mostly want cutting tools. As it
gets hotter, you get a darker brown, followed by purple, and then
deep blue. As the colors progress, the steel gets softer but less
brittle.
You can’t really see the oxide rainbow on the burnt oxide layer left
over from heating steel to red hot, so the quick scrub with the
emery is to get the black oxide layer off so that you can see the
oxide rainbow as it develops.
What I normally do is quench the whole tool to dead cold, and then
carefully reheat the shaft from the center, with a torch, so that I
can build the heat into the shaft slowly, and control how fast the
heat migrates down to the working end. This gives me better control
of the exact color (hardness) that I get at the working end.
Leonid’s technique just uses the residual heat in the tail end of the
shaft to reheat and temper the working end, rather than using a
torch. The advantage is that it’s quicker. The drawback is that you
have no time for screwups, hesitations, or thinking about it. You
have a second or two to emery the end, and then another 3-5 seconds
before the heat comes rushing back into the working end of the punch.
There will be much more heat, coming in much faster, so you really
have to know what color you want, and be ready to quench it off
instantly when you get there.
Like I said, if you really know what you’re doing, this works great.
If not, quench the whole thing to dead cold, emery the end, and then
hit the middle with a torch. Once you see the rainbow starting in the
middle, back the torch away a few inches, and the heat colors will
move very slowly up the punch. That’ll give you plenty of time to get
it into the water once you’ve got the right color at the tip. (Make
sure you heat the tail of the punch, to make sure it’s soft. (or
don’t heat it to red in the first place.))
One final trick: I normally rub the working tip of my punches in a
slurry of Ivory handsoap before heating them to red hot. It forms a
sort of flux that blasts away when you quench the tool, taking the
dark oxide with it. (more or less) Saves having to emery the end,
and really helps with making the “hot tail” trick work better. Just
get a bar of hand soap wet, and rub the tool across the top of it a
couple of times to get it coated in soap.
Regards,
Brian.
Water