lead bath spring tempering

[jerrywh]

Lead bath spring tempering.
  If you don't have a pyrometer of a furnace the next best thing is a lead thermometer. You can buy one on Amazon of EBay for about $25.00 t0 $35.00.
 You need a lead pot and at least 5 lbs. of pure lead. When doing this  hold the spring by wrapping a piece of iron wire around it so as to have a good secure hold on it.
  First thing is to heat the spring to a cherry red heat. Do not go to a bright orange but just a good red heat. Don't be in a hurry. Heat it evenly throughout and them quench it in transmission oil or 10w motor oil.  Start heating the lead pot before you harden the spring so it will at least up to 300 or 400 deg. before you quench the spring. After quenching the spring immediately put it on top of the hot lead.   
 When the lead melts hold the spring under the surface and use the thermometer to check and raise the temp to 720 deg. F and stir it so that the temp will be even in the lead bath. After the lead reaches 720° you can shut the heat off and let the lead set up while holding the spring under the surface. The lead doesn't have to set up entirely. The object of this is to keep the spring at that temp, for the required length of time. If you can maintain the temp of 720 for approximately 12 to 20 minutes that is all that is required. Once the lead is partially set up turn the heat back on and re melt it until the spring floats to the top. Then remove the spring from the lead bath. Some lead may be stuck to the spring so while it is still hot just give it a few hits on a wooden board to knock off the lead. The lead will not stick hard to the spring because of the oil that was on it. Then just let it cool naturally and it twill be ready to go.
 Before I had a furnace I used this method for 30 years or more. I am positive that many of the 18th century gun makers used this process. What gave me the clue was this. While working on some original locks I noticed that some lead was stuck in the bend on several of them. 

[D. Taylor Sapergia]

This is wonderful information, generously provided by he-who-knows stuff.  Thanks Jerry.

[P.W.Berkuta]

My first 5 springs that I made back in the late 60 were tempered with a torch by color - all broke when tested. The next bunch of springs were tempered by the "burning off oil" method - I had a 80% success rate. The method I now use is the "lead bath" method and now have 100% success.

[WadePatton]

Thanks Jerry! 

[Bob Roller]

My first 5 springs that I made back in the late 60 were tempered with a torch by color - all broke when tested. The next bunch of springs were tempered by the "burning off oil" method - I had a 80% success rate. The method I now use is the "lead bath" method and now have 100% success.

My experience making springs goes back over 50 years and I have used the color/draw with about 99.9% success.
Maybe some people have different perceptions of the same color,blue.Are there any eye surgeons on this
forum that might be able to give some input on this.

Bob Roller

[smylee grouch]

Jerry: would the times of submersion for the spring vary much with the thickness of the spring?

[Bob Roller]

Lead bath spring tempering.
  If you don't have a pyrometer of a furnace the next best thing is a lead thermometer. You can buy one on Amazon of EBay for about $25.00 t0 $35.00.
 You need a lead pot and at least 5 lbs. of pure lead. When doing this  hold the spring by wrapping a piece of iron wire around it so as to have a good secure hold on it.
  First thing is to heat the spring to a cherry red heat. Do not go to a bright orange but just a good red heat. Don't be in a hurry. Heat it evenly throughout and them quench it in transmission oil or 10w motor oil.  Start heating the lead pot before you harden the spring so it will at least up to 300 or 400 deg. before you quench the spring. After quenching the spring immediately put it on top of the hot lead.   
 When the lead melts hold the spring under the surface and use the thermometer to check and raise the temp to 720 deg. F and stir it so that the temp will be even in the lead bath. After the lead reaches 720° you can shut the heat off and let the lead set up while holding the spring under the surface. The lead doesn't have to set up entirely. The object of this is to keep the spring at that temp, for the required length of time. If you can maintain the temp of 720 for approximately 12 to 20 minutes that is all that is required. Once the lead is partially set up turn the heat back on and re melt it until the spring floats to the top. Then remove the spring from the lead bath. Some lead may be stuck to the spring so while it is still hot just give it a few hits on a wooden board to knock off the lead. The lead will not stick hard to the spring because of the oil that was on it. Then just let it cool naturally and it twill be ready to go.
 Before I had a furnace I used this method for 30 years or more. I am positive that many of the 18th century gun makers used this process. What gave me the clue was this. While working on some original locks I noticed that some lead was stuck in the bend on several of them. 

THIS is more trouble than it's worth based on experience with the method I have used for decades.
The last mainspring I replaced on one of my locks was a flintlock made before 1970 and it had an
odd color and broke in the center of the long lower limb.

Bob Roller

[Joe S.]

forgive my ignorance on the subject but do you do this with all springs? with any locks you buy,build and if not what are you looking for that tells you it needs this treatment,thanks

[jerrywh]

 Tempering requires a certain amount of time in order for the steel to complete a transformation throughout.
 The General rule I use is once the steel reaches the proper temp. 12 minutes for each 1/8" of thickness. The steel can be held at the proper temp. for a prolonged period of time and will not effect the outcome. In other word even if it was held at 720° for two hours it would still have the same result as if held for 20 minutes. Sometimes when in doubt I will temper a spring twice.
  I don't temper springs that come with Chamber's locks. They are as good as can be. I sometimes modify locks and springs on other locks and than re heat treat them. For example I am now making a special lock for a Russian Jaeger. The frizzen spring will be engraved and customized. I only had one spring break lately and it was caused by using blue remover on it. It just snapped sitting on my bench at half cock. Sometimes lock kit springs are tempered and sometimes not. Blackley springs are not tempered. All the ones I have cast are not. In any case if you know how there is nothing to fear.
This is not anything I thought up. It has been an established process for hundreds of years. There is so much false info out there that is the biggest problem.
  Bob and others have learned a different way to produce the same results but carbon steel is steel that is what it is and the process is like a law of physics. The temps are required and so is the time requirement. It is no different than the fact that water boils at 212° F at sea level. How can somebody say it boils at 190° for them?  You can't cook a biscuit at 350° for 1 minute. There is a time factor.  
  
   What causes a lot of confusion over spring tempering is the different type of springs. Coil and clock springs temper at a lower temp, than V or flat springs and torsion springs are even different. If a V spring were made of 6150 and you tempered it at 600° it might last indefinitely depends on how much it flexes , how thick it is and other factors.. You can get by with more on say 1075 than you can on 1095 or 01 steel. But the 720° will always work.  If you look up spring tempering temps. You will get a general answer and it might not work for a V spring but it would be perfect for a coil spring. That is another problem.

[Mark Elliott]

This is how my grandfather taught me to heat treat springs and how I did it for many years until I got a heat treat furnace.   

[David Rase]

I have a heat treat oven and I still use the lead bath method.  I have found the lead bath is quicker than firing up my oven.  If I had better color vision, I might be able to use the color/draw method.  I can identify colors but not shades, especially the earth tones. 
I have to have my wife come out and tell me what color a stock is when I am finished staining it. 
David

[smylee grouch]

Jerry, thanks for that explanation. I have done the lead bath on a few small springs and patch knives but never knew if they would last or if I had done them right. So far so good. Thanks again.

[L. Akers]

I've been using a lead bath to temper springs for awhile.  I wrap the springs (I do several at once) in aluminum foil to keep the lead from sticking.  My springs don't have oil on them because I have polished them again after hardening--like to see the pretty "spring blue" color.  I was initially concerned the aluminum would leach into the lead but research said no worries.  I let a batch of springs soak for an hour held down in the lead with a stainless steel rod then remove them from the pot and allow to cool.  I haven't had one break since I started using this tempering method.

[Joe S.]

OK......but are we just making a better spring in terms of longevity or are we curing a problem with store bought parts? I get it everything one can do to make a better lock..........What I'm asking is what to look for to warrant this treatment.You said Chamber's locks are good to go,the rest?

[jerrywh]

 I haven't had any trouble with any of the leading production locks as far as springs go. I did change some of the L&R springs by giving them some more spread to increase the tension. One advantage of knowing this is you don't have to worry if the spring needs altering or heat treating. You just do it.

[Joe S.]

Good point thanks Jerry

[D. Taylor Sapergia]

I love this statement:  you can't back a biscuit at 350 for 1 minute.

That says an enormous volume.  the hardened spring needs to soak at tempering temperature for a period of time to make it uniform throughout.  So make the soak longer to be absolutely sure.  A few more minutes soaking at 720 deg. is better than filing out a new one because you were impatient.

I seem to be frequently changing the tension on frizzen springs.  So leaning how to temper them correctly has been paramount.  thanks Jerry;  great stuff.

[FDR]

I just wire the spring to a small block of tungsten (heavier than lead) to hold the spring down. Don't forget the wire to retrieve the bundle. Pouring out a whole pot of lead to get the spring is not fun! Ask me how I know.
By the way this heat treat method works great on beryllium copper springs. Very non-traditional but they never break.

Fred

[Jim Kibler]

There's nothing magical about a particular temperature such as 720 F.  A better approach is to consider the alloy (grade of material) and pick a tempering temperature based on a desired hardness.  Reference tempering charts for this.  A good aim point is the low to mid 40's on the HRC scale.  The tempering temperature that will yield this for 6150 is quite different than that for O1, for example.

Jim

[Joe S]

Rather than rely on color when heating the spring, I use a magnet.  Quench when the magnet will no longer stick to the spring.

[Jim Kibler]

Non-magnetic is a good guide, but you must heat a little hotter than this point.  The non-magnetic point is the "Curie Temperature" and  independent of any phase changes.  Without looking temperatures up, if you heat another 100 degrees F above the non-magnetic point you should generally be good.  This would be in the range of 1500 F.

[WadePatton]

... It is no different than the fact that water boils at 212° F at sea level. How can somebody say it boils at 190° for them?  ...

Two ways this can be.  Elevation and instrumental error.  Funny thing is I JUST watched the temp of my tea kettle and saw it boil at just over 200, well short of 212(f).  But I'm at 1100' and the barometer is at 30.07".  I'm sure the high-plains and mtn dwellers see lower boiling temps.  But also I was only using a single, non-certified thermometer.   When things are "more critical" I tend to use at least two thermometers for reference.

Why was I measuring water temp?  Coffee nut just re-checking the "system" and running a new blend.   

But also anyone reading up here who doesn't have a bit of heat/colors experience, do remember to polish out that steel and read the colors in a subdued light. 

I had some troubles with a small spring a while back but didn't try the lead bath.  My lead pot is going to the workshop today.  (tired of kicking it around the kitchen  ).

[JCKelly]

Thank you, jerrywh, this spring tempering post makes good sense, to this metallurgist. It is now in my files.

Finding lead stuck in the bend of original springs is good enough proof for me.

I suspect those old steel springs were "shear steel" roughly comparable to our 1070 or 1074.

I have seen a couple of beautiful new-made springs broken because they were too #$%&  hard, about Rockwell C50. Dunno how he quenched them.The maker tempered them in lead, which melts at 621F. Too cool. Ahhh . . . get a lead thermometer for a few bucks & get it up hotter..   

I might add that a good spring tempering temperature does depend upon how hard the thing was to start - which is why it is good to do as you say, quench in oil rather than water.

Carbon steels such as 1095, or the most forgiving - something in the range 1070 to 1075 - are more likely to work out in your home shop.

My head is a little resistant to moving from the industrial practice with which I am familiar, to what works best at home. Guess if I get back to my shop I may get a lead thermometer & some 10 wt oil.

Things like O1 or 6150 are great for industrial use, but oil quenching them may get them too hard for this tempering procedure. Unless you have already figured out how to work with alloy, I would suggest staying with your favorite carbon steel. If you must have a tool steel, find some W1. It is like a high class 1095. Sometimes has a touch of  vanadium (symbol - V) which is helpful. 

Oh, as an aside - my Grandma used a pressure cooker, as she lived in the beautiful hills of Western Pennsylvania.  Water does not boil at 212F there. Lead still melts the same, though.

[Bob Roller]

Thank you, jerrywh, this spring tempering post makes good sense, to this metallurgist. It is now in my files.

Finding lead stuck in the bend of original springs is good enough proof for me.

I suspect those old steel springs were "shear steel" roughly comparable to our 1070 or 1074.

I have seen a couple of beautiful new-made springs broken because they were too #$%&  hard, about Rockwell C50. Dunno how he quenched them.The maker tempered them in lead, which melts at 621F. Too cool. Ahhh . . . get a lead thermometer for a few bucks & get it up hotter..  

I've used 1075 for over 50 years with no major problems reported.Recently I wondered how MANY springs I have made
from about 350 pounds of this steel.

Bob Roller

I might add that a good spring tempering temperature does depend upon how hard the thing was to start - which is why it is good to do as you say, quench in oil rather than water.

Carbon steels such as 1095, or the most forgiving - something in the range 1070 to 1075 - are more likely to work out in your home shop.

My head is a little resistant to moving from the industrial practice with which I am familiar, to what works best at home. Guess if I get back to my shop I may get a lead thermometer & some 10 wt oil.

Things like O1 or 6150 are great for industrial use, but oil quenching them may get them too hard for this tempering procedure. Unless you have already figured out how to work with alloy, I would suggest staying with your favorite carbon steel. If you must have a tool steel, find some W1. It is like a high class 1095. Sometimes has a touch of  vanadium (symbol - V) which is helpful.  

Oh, as an aside - my Grandma used a pressure cooker, as she lived in the beautiful hills of Western Pennsylvania.  Water does not boil at 212F there. Lead still melts the same, though.

[jerrywh]

1075 is a real good steel for springs. I used it for a long time also. But I never used 350 lbs.
  Might be of some help to the newer guys to know what happens to a spring when it flexes, where the stress is and how to reduce the stress or equally distribute it.
  Some things don't apply to gun springs but it is of interest to know why some larger springs temper at a much higher temp than smaller ones.ETC.