Hardening and Tempering Notes
It has been my experience that the secret to
good flintlocks is in the polishing and hardening, especially on early locks
that do not have internal bridles. You can double the speed on an early lock
by hardening the cock, tumbler and lock plate you can also speed up later
locks by making sure the lock plates are hardened. We use 4140 steel on all
our lock parts except frizzens and springs which are 6150. These are oil
hardening steels, but we don't recommend oil hardening, but you will find
that if you case-harden the lock plate, internals, and frizzen then use a
water quench it will give you a finer finish and smoother bearing surface.
You are not adding anymore carbon by doing this, but you are keeping the
parts from losing any carbon while you are bringing the part up to the
correct heat range (1650° to 1675° or very bright reddish orange). You will
find this especially true with frizzens where carbon content is very
critical. A case-hardened and water quenched 6150 or 1095 steel frizzen will
spark 10 times better and hotter than an oil hardened one. Always be sure to
draw the tail of the frizzen to a deep blue color up into the edge of the
pan cover area.
To harden a spring we use a water quench. Use a propane torch or a rich
flame on an oxyacetylene torch. Bring the spring slowly up to a very bright
red almost orange (1500°), making sure the spring is a consistent color all
over, then drop it into a container of room temperature water. Handle the
spring carefully, as it is now glass hard. Polish the spring. For tempering
the spring use an area where the light is not too bright so you can see the
color changes easily. Start heating the spring from the largest end first
going over the entire spring and the colors will start out a straw or gold
color going into a scarlet or purplish color, then into a shinny deep blue
color, continue heating slowly and this blue will disappear and start all
over with a clear shinny color, then back into the gold color, then the
scarlet or purplish color (approx. 700°), then into a dark blue black
(approx. 750°). As soon as you get the blue black color even lay the spring
down on a piece of wood an let it cool, when cooled it will be a perfect
spring. If you find that it does not have enough tension, re-harden and
re-temper to just as the blue black color appears, on smaller springs you
can stop at the purplish color (approx. 725°). I have re-hardened and
re-tempered some springs 8 or 9 times to get just the right feel. Always
polish the bearing surface on the foot of the spring. If you do not want to
try hardening your springs just return them after you fit and polish them
and we will harden and temper them for you.
On early locks without internal bridles try to get as close a fit on the
tumbler, lock plate and cock as possible with no binding. Be sure to harden
all three. These early type locks will last you almost forever if you take
time on these points in the beginning. When you are polishing use “wet or
dry” emery paper, go all the way to 600 or 800 grit before you ever use a
buffing wheel so as to keep everything square and true. Also a little more
polishing after hardening everything because the better the finish, the
faster the lock. As a rule of thumb polish every piece that moves or
something moves on.
Flints are also important in having an excellent lock. Use good flints that
are large enough. Early locks and military locks used larger flints then we
tend to put in them today. If your frizzen doesn't kick all the way open,
try using a larger flint instead of grinding on the camming surface, or put
your flint in bottom side up as some early locks were made to use spall type
flints which have no top or bottom. The shaped flints we have today did not
come into major use until after 1800. The British were still using chips and
spall type flints in the war of 1812.