lead bath spring tempering

[LRB]

  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.

  Jerry, I really do not think large springs require higher heat for temper. Can you give an example? It might require a little more time for the heat to soak in and even out, but it should not require higher heat. If it seems to you that it does, I would suggest looking for other possible factors involved.

[Bob Roller]

jerrywh,
I used to repair old locks back when I was trying to get started and made springs for anything that I could.
Old revolvers were commonly springless and these gave me some experience about general "Gumsmiffing"
that made me quit it forever. Old !@#$% bringing in a gun and then wanting to pay next to nothing for a job
they couldn't begin to do. Kind of like Friendship in the mid to late 1950's,always some legendary "old man"
story about making springs from God knows what for nearly nothing. I challenged that then and still do,
it's BS from people who won't pay for anything.

Bob Roller

[Dphariss]

I make springs from 0-1, 1095 or 1070ish. Many times it depends on whats in the shop. 1070 is the easiest to form though I use the same quench and temper for all of them.
I quench in WARMED light weight oil. something like ATF or 10w with a good dose of Marvels Mystry Oil to thin it even more. I heat a block of steel to near red and put that in the oil before I even heat the spring. Why? Warm oil will cool faster and more uniformly than cold oil. I like it to be nicely warm but not very hot to the touch.
Temper? Small springs I color temper with a torch after a good polish.
Heavier springs I heat in a vat (made from a piece of conduit with ends welded on) of Potassium Nitrate till I get the uniform color I want. Blue just starting into lighter blue/blue grey. The Nitrate bath brings the temp up slower than one might think since it initially forms a thick shell on the cold part.
Heat soak? Uniform temp? Soak times only apply to thick thicker items than gun springs will be. Even when using O-1 which DOES require specific soak times for thicker sections reading ALL the info will show that this is for thicknesses well over that seen in any gun spring.

I doubt that the makers in Allentown or Bedford or even Philadelphia or even London in the 18th C. had high temp thermometers or any thermometer for that matter.  If the part is not completely oil free they could not even see the colors since the colors will not form on a contaminated part. I don't know how they could judge temp short of color. So while like the nitrate a lead bath will give a good way to heat the part. The thin sections will heat first. So without control of the temp for the bath then one must tip the part to leave the thin sections out the bath to keep them from overheating. I don't know how they would do this other than by color and color belies long soaks since it is hard to control the temp of lead over a fire  especially since it will cool very slowly if it gets a little too hot in the forge or whatever heat source would have been used back in the day.
Biscuits are not springs and other than their ALSO being checked for "done" by color, golden brown in most cases, there is very little cross over in the two processes. Nor do biscuits reach 350 or 400 internally or they would be inedible.
Now.... This how "I" do it. This does not make it right or the only way. Its a reference for people wanting to know how to make springs. People learn how to do things and tend to stay with what works. People that make springs successfully don't really need any of this. But for the neophyte its important that they understand that they may need to find something that works for them and the equipment they have available. Potassium Nitrate in granular form can be ordered from companies selling supplies for people making their own biodiesel.
Such as https://www.dudadiesel.com/search.php?query=%22potassium+nitrate%22
Note that parts immersed in lead or nitrate must NOT have any water on them as this can cause a violent steam explosion. If it doubt preheat the part slightly to drive off any water other solvent, like alcohol if the part is degreased before immersion. The use a of a full face shield, long sleaves and leather gloves is a good idea as well.

Dan

A gunsmith friend has small poster board on the wall with several broken mainsprings, all apparently for the same lock.
Below each broken spring is the word "$#*&!".

[jerrywh]

 Lead bath tempering is not the only way to temper a spring but this thread is on lead bath tempering.
Another method is Using a potassium or Sodium nitrate bath as suggested by Dan. If the bath is at the proper temp it does not matter how long the sporing is in the bath as long as it has sufficient time for transformation to take place. The time matters. If one says it doesn't they should be asked just how long was the spring in the bath. Transformation on the molecular level takes time. Any metallurgist will tell you that.
  Perhaps a thread should be done on tempering by color as well as the burning oil process. There is a science to both. There is also a science to what goes on in a V spring when it is flexed.  
 Let me say this, There is no danger of a spring breaking if it is left at the tempering temp too long nor will it weaken it. However there is a danger if it is not heated long enough. Therefore what do you gain by saving 10 minutes and what do you stand to loose. If you look up tempering prceedures on any steel manufacturer's web site it will always list a time factor.
   LRB or wick. When I said that some big springs temper at a higher temp than smaller ones I am not talking about gun springs. I should have clarified that . Large springs that have a thickness of 1/2" to 1" in thickness need a softer temper because of the increased stress on the  stretch side. Some people do not realize that the steel actually stretches on one side when the spring stretches  a thick spring  needs more elongation ability to do that. That is why steel manufacturers recommend tempering temps as high as 1300° on some springs.
  Like every subject there is usually more to know than one might think. It is also why car springs are composed of multiple leaves. One leaf that thick cannot be made to stretch that far on the stretch side. Stretch side is my own terminology and probably isn't the correct definition but that is what they do.

[bob in the woods]

Thank you to all contributing to this .  Gosh knows that I've had my share of spring failures.  Trying to "fix" springs for locks brought to me has always been trouble.
I try not to take that on anymore, since most aren't eager to pay me to replace the one I broke .       Putting the piece in a can of oil and burning it off seemed to work OK for most of these, but the lead bath method has been the best so far.

[JCKelly]

Somewhat off-topic, which I believe regards tempering springs so they will not break:

The stiffness of the spring, how hard it is to cock the thing or move the frizzen, has nothing at all to do with how hard it is. If you need to weaken a spring, make it just a little thinner. If you need a stiffer spring, make a new one a little thicker.

Tempering temperature or hardness has nothing to do with how stiff a spring is.

If tempered too hot/too soft, the spring may take a set.

If tempered too cool/too hard, the spring will break. Sometimes it does this while in the lock resting on your bench.

I suppose you all know this, but I have had quite a job over half a century to convince various engineers that this is true.

As far as design goes, look at old springs in good quality locks, including  Civil War Springfield locks. Where they bevel an edge is not just for pretty, it is to reduce the chance of it cracking in long use.

The $2 lecture is a lot longer and more tedious.

Design, design, design. 19th century guys knew how to design things, like leaf springs better than do aerospace guys whom I have known. Likewise they could design a steam locomotive driving rod properly, unlike Henry Ford Village does when replacing such a part.

[Bob Roller]

Somewhat off-topic, which I believe regards tempering springs so they will not break:

The stiffness of the spring, how hard it is to cock the thing or move the frizzen, has nothing at all to do with how hard it is. If you need to weaken a spring, make it just a little thinner. If you need a stiffer spring, make a new one a little thicker.

Tempering temperature or hardness has nothing to do with how stiff a spring is.

If tempered too hot/too soft, the spring may take a set.

If tempered too cool/too hard, the spring will break. Sometimes it does this while in the lock resting on your bench.

I suppose you all know this, but I have had quite a job over half a century to convince various engineers that this is true.

As far as design goes, look at old springs in good quality locks, including  Civil War Springfield locks. Where they bevel an edge is not just for pretty, it is to reduce the chance of it cracking in long use.

The $2 lecture is a lot longer and more tedious.

Design, design, design. 19th century guys knew how to design things, like leaf springs better than do aerospace guys whom I have known. Likewise they could design a steam locomotive driving rod properly, unlike Henry Ford Village does when replacing such a part.

I have heard of springs breaking with the lock being inactive in the gun or on the bench. In the mid 1950's some gunsmiths
were using automobile leaf springs as a source of material and this was a common occurrence. Glen Napier and I were in
his shop one day talking about this and we both heard a "tick" and Glen said the spring in that lock just broke and he was right.
Design IS the whole thing. I have used fine English sporting rifle locks for this and it is the answer.One English man living in
Wolverhampton told me that spring filing is a separate trade or skill and I know he's right. The beveled edges on a mainspring
is not only good looking but the filing process will or can detect hard spots in the spring.
The tempering is another skill set and what works for me does just fine and the absence of returned locks tells me I am doing
something right. If other methods work for other craftsmen that's fine and I won't argue about it.RESULTS are what they are,
good or bad.

Bob Roller

[westbj2]

As I read thru this thread, a couple additional factors come to mind.  One of them I still dont quite understand.

Early on in my spring making I was told to anneal the work after forging and bending.  Bring to a dull red and hold for 3 minutes then allow to cool until touchable.  Then proceed to hardening.

Here is the mystery using a lead bath to draw the spring.  Part was a very small spring (using 1095) with and integral screw eye for the secondary sear of a Purdey sidelock.  Size was about .180" high,  .015" thick tapering to about .007" at the tip and about  .350" long.   Using the same soak time as for larger springs  (20 min) resulted in a part that had become partially annealed.  After several more attempts and rehardening, just 3 minutes in the lead produced a good spring.
Somehow, the volume of material seems related to soak time. . . .
Jim

[Bob Roller]

As I read thru this thread, a couple additional factors come to mind.  One of them I still dont quite understand.

Early on in my spring making I was told to anneal the work after forging and bending.  Bring to a dull red and hold for 3 minutes then allow to cool until touchable.  Then proceed to hardening.

Here is the mystery using a lead bath to draw the spring.  Part was a very small spring (using 1095) with and integral screw eye for the secondary sear of a Purdey sidelock.  Size was about .180" high,  .015" thick tapering to about .007" at the tip and about  .350" long.   Using the same soak time as for larger springs  (20 min) resulted in a part that had become partially annealed.  After several more attempts and rehardening, just 3 minutes in the lead produced a good spring.
Somehow, the volume of material seems related to soak time. . . .
Jim


I would like to see a picture of the secondary sear and what is the purpose of it?

Bob Roller

[LRB]

As I read thru this thread, a couple additional factors come to mind.  One of them I still dont quite understand.

Early on in my spring making I was told to anneal the work after forging and bending.  Bring to a dull red and hold for 3 minutes then allow to cool until touchable.  Then proceed to hardening.

Here is the mystery using a lead bath to draw the spring.  Part was a very small spring (using 1095) with and integral screw eye for the secondary sear of a Purdey sidelock.  Size was about .180" high,  .015" thick tapering to about .007" at the tip and about  .350" long.   Using the same soak time as for larger springs  (20 min) resulted in a part that had become partially annealed.  After several more attempts and rehardening, just 3 minutes in the lead produced a good spring.
Somehow, the volume of material seems related to soak time. . . .
Jim

   I am going to open myself up to naysayers, and possible ridicule, but here goes, believe this or not. You can research it for yourselves,  I believe your problem was in not getting the spring as hard as it should have been when you quench it the first few times. 1095 is a difficult steel to bring to it's maximum hardness, and needs special attention to get any where near it, without using a brine quench. To lessen the chance of cracking in brine, a very fast cooling oil will do well enough. Ideally, to reach max hard, the 1095 must cool to below 900°, from about 1475°, in about .6/.8, of one second. Only a brine quench will allow that kind of speed cooling. The use of just any oil will not do the job. The best oils would be commercial types rated for hi speed cooling, but they are not cheap. The only other type tested and shown to be adequate for 1095 is canola cooking oil. Not the best, but will get you by if heated to about 130° to make it thinner and cool faster. If the 1095 steel does not cool to below 900°, in a time frame of under a couple of seconds of quench time, your steel will be a mix of hard, and soft steel. Much like minute islands of hard in a sea of soft. If you test with a file, it will tell you it is all hard, because the hard islands will not allow the file to cut the soft sea.  My guess is that you lost too much heat getting the spring into the quench to start with, small thin pieces lose heat fast, and that your oil was not fast enough to cool it properly when you did. With multiple attempts, you finally got lucky for the spring to get hard enough to work. It was not the temper soak time being the problem. As said previously, extra time in temp does not soften the steel more after it reaches it's predetermined goal.

[westbj2]

Interesting information about 1095.  Because the spring was so small the major issue was heating it to correct red without going over to orange and sparks.   Heated it with spring lying on a piece of 1/4" plate and then knocked it off into transmission fluid quench.  Spring fell 4-5 inches which could well have cooled it too much.

Bob,  In the link enclosed you can see that the sear is split.  Two different engagement points...lock cannot fire unless both sears allow movement at the same time

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=275755&Main=239731
you will have to paste the address in your browser

[hudson]

Following this thread has been very informative. I find interesting the various methods used. I consider using the color method an art form and have used it. With the few spring I have made, results have been on the plus side. As I recall in Hatchers Notebook he notes the difference in jugging color from an over cast day to a sunny day. Granted he was talking about a different alloy. The point being lighting may make difference. I now have a heat-treat furnace to play with. But kind of like the lead bath idea.

[LRB]

 The problem with using color for spring temper is that the color for spring temper is beyond colors at a neutral gray. You lose color before the steel is at the correct temperature. Another point is that not everyone sees color exactly the same.  Judging temps at red heats and above should be done in a dark, or very dim lighted area. Good light is needed to judge the lower than red colors.

[Bob Roller]

Following this thread has been very informative. I find interesting the various methods used. I consider using the color method an art form and have used it. With the few spring I have made, results have been on the plus side. As I recall in Hatchers Notebook he notes the difference in jugging color from an over cast day to a sunny day. Granted he was talking about a different alloy. The point being lighting may make difference. I now have a heat-treat furnace to play with. But kind of like the lead bath idea.

I have never noticed or paid any attention to the weather outside the shop,sunny,gloomy
it makes no difference to me.

Bob Roller

[hudson]

Now that I think back when I mentioned  Hatchers Notebook, tempiture difference do to with an overcast versed sunny day. It had to do with furnace heat. In other words pertaining to quench or initial hardening. This was considered one of the reasons the early Springfield actions failed. My mistake.

[Bob Roller]

Interesting information about 1095.  Because the spring was so small the major issue was heating it to correct red without going over to orange and sparks.   Heated it with spring lying on a piece of 1/4" plate and then knocked it off into transmission fluid quench.  Spring fell 4-5 inches which could well have cooled it too much.

Bob,  In the link enclosed you can see that the sear is split.  Two different engagement points...lock cannot fire unless both sears allow movement at the same time

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=275755&Main=239731
you will have to paste the address in your browser

That split sear solved a problem that never was there to begun with.Only one full cock notch as near as I
can see. Many thanks for posting the pictures.

Bob Roller

[jerrywh]

 I have a correction to make . I previously stated that I thought Chambers tempered his springs at 800°F
 I have been informed that the tempers them at about 750° and is presently using 6150 steel.