Thermometer for lead pot tempering of lock parts

[Gregory]

I have a Siler kit that I need to heat and temper the parts.  I have an electric lead casting pot (Lee_ 120 volts/500 watts) which seems would be good way for the tempering.  I do not have a lead thermometer.  What would you recommend?
Thanks,
Greg

[davec2]

Least expensive option would be one like this

https://www.mcmaster.com/thermometers/maximum-temperature~750degreesf/clip-on-thermometers-8/

[TommyG]

Not having a controlled oven (at least not yet), I often use my lead pot, a hot plate with a skillet of sand, or a plain old small charcoal grill for tempering and annealing.  Of course you will be limited to what you can do, but not by much IMO.  I simply use a Lyman digital thermometer with the probe.  I recently hardened and tempered a set of DS triggers.  The problem with the lead pot is lead melts around 630 degrees F.   So for something like triggers and various lock parts, that is probably the top end of the tempering temperature and will require you babysit the pot to keep the temp dwelling in that range.  For parts like frizzens and various tools I make, I use the skillet filled with sand on a hot plate as I can dwell that temp around 350-400 F no problem, but the hot plate only gets me to around 500 degrees.  The lead pot works great for tempering springs also.  But with any of these you will need to babysit the temperature for the required time length.  Also, I use an oxy-acetylene torch to initially harden. 

[Scota4570]

Linotype will melt at about 460*F.

[martin9]

I just did this for a siler with my lead pot. I was surprised how accurate the thermostat on my lyman pot is. I just used an oven thermometer..the kind that hangs on the rack. I just stuck it straight in the lead. Once it stayed at the same temp for 30 minutes or so I put my parts in and timed them per the siler instructions.

[jerrywh]

Personally I don't trust the temp gauge on a lead pot. WHY? because they just don't need to be very accurate so they probably aren't.  However each individual one is probably a small percentage off or on one way or another.  If you want to take a chance on making some new parts then Go for it.  A lead thermometer is cheap insurance and they are pretty accurate.  Springs and lock parts don't really require extreme accuracy anyway. 10° or even 20° either way probably won't make a noticeable difference. I checked my lead thermometers with a couple of pyrometers they were very close.  Let the argument begin.

[Gregory]

Thanks for all the information.  I think a thermometer as recommended would be useful to me.
Greg

[T*O*F]

I checked my lead thermometers with a couple of pedometers they were very close.  Let the argument begin.

OK, Jerry,
Just for arguments sake, how do you check temperature with a device used for measuring how many steps you take?

[davec2]

Not sure how Jerry does it, but I have checked my lead pot with one of these:

https://www.mcmaster.com/40255K43/

About $600.  I can use the instrument to SET the lead pot at a particular temperature, but if I just go by the knob on the lead pot thermostat (which is not very precisely marked for obvious reasons) the temperature can be 100 degrees or more off of where I think it is.  Now if you are just at the very edge of liquidus (i.e. the lead is just melted) or at the boiling point of lead (3,180 degrees F), then you will know where you are fairly accurately temperature wise.  Anywhere in between is a bit of a $#@* shoot without an accurate temperature measurement instrument.

[P.W.Berkuta]

Try here <https://www.rotometals.com/lead-bullet-casting-thermometer-6>

[Scota4570]

If you want to verify your thermometer you can use these:


https://www.amazon.com/Tempil-28019-Surface-Temperature-Indicator/dp/B00P18EIAY/ref=sr_1_1?dchild=1&keywords=temperature%2Bcrayon&qid=1593732266&sr=8-1&th=1

[T*O*F]

Not sure how Jerry does it,

I think he meant pyrometer, not pedometer.

[Bob Roller]

This lead pot idea is one I have never given any thought to and my own primitive
ways seem to have worked well for a loooong time.I learned watching color changes
from George Killen who was a gunsmith here.He said he learned it from a black man
called "Uncle Bev" when he was about 11 years old in 1900.

Bob Roller

[martin9]

I'd like to hear more about this. Do you heat to cherry red first, quench and then heat for the color change to temper?  What colors are you looking for on say the tumbler?
Thanks, Wes

[Bob Roller]

I'd like to hear more about this. Do you heat to cherry red first, quench and then heat for the color change to temper?  What colors are you looking for on say the tumbler?
Thanks, Wes

I heat to a bright orange using a Prestolite "B"gas torch.For sears,flys and tumblers AND
sear springs I use the #3 tip and for mainsprings and frizzens I use the #5 tip.
I quench in hydraulic jack oil and then after the parts cool I get them out with a magnet
and swish them in kerosene and dry with a shop cloth or old face cloth from the house.
Polish with fine emery cloth and 400 grit aluminum oxide and then use a common Bernz-O-Matic
torch with a home made adapter to pin point the flame to a 1/4 inch circle.
My tumblers were made from 1144 "stressproof"which machines like 12L14 and hardens like drill
rod/0-1.I watch the color until it starts to go into a "straw"color and when it goes to that point I
dropped the tumbler into a can of kerosene.I do the same thing with the fly and sear which are
both 0-1.
I have NO idea what these cast parts are made from and rejected these parts over 50 years ago because of dubious
quality control from foundries who hadn't the foggiest idea as to the final use of these parts.
ALL of my lock mechanisms were made as described here and they are all over the world with no problems
reported.I am no longer making locks of any kind and am now making some double set triggers on an
on again off again schedule.The trigger springs are made from annealed 1075 as were the main and sear
springs in the lock and again,no reported problems with locks still working after 50+years.Triggers are
cold finished 1018 and finished by case hardening.
Don't know if this helps or not but for what it's worth,here it is.

Bob Roller

[P.W.Berkuta]

Heat treating by color is very subjective. The colors are effected by the surrounding available light, ones eyesight, and the type of carbon steel you are using.  What looks like cherry red to one is not cherry red to another. Cherry red is not the color you want as you upper most hardening temperature on most carbon steel anyway.

You will have to practice on scraps of the same steel to get the "feel" of the upper temperature and then the tempering temperature otherwise you may end up with a brittle or soft part. Go on the web or buy a book on hardening and tempering of carbon steel in it there will be steel colors associated with temperatures. Good luck .

[martin9]

Thank you! Of course you're right about the cast parts but it's still good info to have. Gonna save this to favorites.
Thanks, Wes

[Bob Roller]

Mr.Berkuta is right but determining the type of material has to be a factor.
I have NO idea what these kit locks are made from and won't even try to
give advice on using them.I have had numerous requests over the years
to put these kits together but having no idea as to what I was looking at
I declined to work on them.The methods I described are labor intensive
and the only thing I can say is that now@84 I have no further interest in
doing any more locks and might get one from Chambers or Kibler to finish
a project that's been laying around too long.

Bob Roller

[jerrywh]

I checked my lead thermometers with a couple of pedometers they were very close.  Let the argument begin.

OK, Jerry,
Just for arguments sake, how do you check temperature with a device used for measuring how many steps you take?

I allowed the spell check to correct my spelling and it replaced [pyrometer ]  with pedrometer.  Jerrywh.

[jerrywh]

  There is nothing wrong with using the color method if you do it right. The problem with it requires a explanation.  Tempering a steel part is similar to cooking a biscuit. You can't just put a biscuit in the oven and heat it to 350° then take it out because it will not be done on the inside. The biscuit must remain at that temp for the required amount of time before it is done throughout. Steel is the same way.  If you heat a tumbler to 600° at first it will turn blue on the outside but it takes a certain amount of time for that temp to penetrate throughout the part. For large parts the generally accepted theory is 12 minutes for each 1/8" of thickness. Most flintlock parts are pretty thin and heat penetrates from all sides therefore let us think about a mainspring for a moment.  An average mainspring is about .090" thick at the thickest part. If heat penetrates from all sides it only must penetrate about .045" to temper the spring. According to my calculations therefore it only takes about 4 t o5 minutes for the spring to be properly tempered throughout at say 725° F.
   SO. If a person heated the spring to the proper color slowly the method would work just fine. The same goes for other parts.  That is why the color method works for some but not others. Some people heat to fast.   

[Bob Roller]

The thickest part of a mainspring is much thicker than .090.
I made my mainsprings from 1/8" thick 1075 and when it
was forged into a mainspring it was about .250 or 1/4".
After the spring was tapered and forged to the shape wanted
I would heat it again and using a forming tool it would be spread
open to establish what would then be the preloading part.
When the spring was tempered it was installed and flex tested
in the assembled lock.Tempering was done after the spring was
pulled from the oil quench,cleaned and polished.It was held by the stud
that goes thru the lock plate and starting at the end of the upper limb
the color change was carefully watched and held for a longer period
at the thick bend and when the color started down toward the claw
it was moved along by the pin pointed fire from the Bernz-O-Matic
mentioned earlier.Whether or not this was a good way I can't say
but decades of unbroken springs must count for something.

Bob Roller

[jerrywh]

Bob. At what point were the springs 1/4" thick? when forged from 1/8" stock?  There seems to be a misunderstanding.

[Bob Roller]

Bob. At what point were the springs 1/4" thick? when forged from 1/8" stock?  There seems to be a misunderstanding.

When a one eighth in piece if steel is bent so the upper and lower
limbs are on top of each other a one quarter inch thickness will
be the result. The lower,longer limb is already tapered to the final
shape and after cooling the upper limb is taper back from the bend
leaving the bend heavy.I roughed in the upper limb taper and the
files it to final shape with a 10'long angle lathe file.

Bob Roller

[jerrywh]

unless they are welded together each leaf is still only 1/8" or less and the bend shrinks. Not worth the debate.
 Another small point is this. If a main spring has a open bend it will temper as I said. If it has a closed bend the bend won't matter because all the flex is in the leaves and the bend doesn't flex.