Mainspring stretch and tempering

[smallpatch]

OK, I don't remember the proper tempering temperature after heating and re-bending a mainspring.

Don G. had a formula that I used a couple of years ago with good results.  Put it in a lead pot, let it solidify, and remelt, then remove.  But I just don't remember how long to hold the temp, and the time to remove.

Any help??

[Dave B]

Lead melts at some where around  600 degrees and all you need is to hold the spring under the surface of the just molten lead for a couple of minutes till its heated through. It is possible to over heat the lead and get the temp too hot making your spring too soft so you want to make sure its tempered just after the lead is completely melted.

[Randall Steffy]

I highly recommend you get a glass/mercury thermometer, cost approx. $30-40, to know what temp your lead is heated. Alloys of lead greatly vary in melt temp and the thermometer makes it so easy to determine your temp. I further suggest 700 degrees and hold there a bit, then let the spring float in lead until cool. But please get the glass thermometer, shielded is even better, and take the guess work out of the equation. I am going by memory on the price, check MSC. I give Stan H. credit for this advise. This is a must buy tool in my book!

[Acer Saccharum]

On McMaster-Carr, the glass thermos went only to 400 deg F.

But the metal dial thermo's go up to 1000 deg F. 

look on middle of page, clip on, clips to the side of your lead pot, 1 3/4" dial dia, 5" stem:

http://www.mcmaster.com/#pipeline-dial-thermometers/=eyi1xj

I'll bet Midway or RCBS sells these or similar along with their lead pots.

[smallpatch]

You're right about the temperature.  Left it there for an hour, put it back in a MS vise.  every time I compress it, it gets weaker and weaker till its back to its original position.

I just need to get this one done, don't have time to wait for a thermometer.

What about in the oven??

[bob in the woods]

I tried the lead pot and it didn't work for me. Spring was mushy every time.  Harden, then place in sardine can with  oil, set a light, when the flame stops, you have your spring.  Works for me.

[keweenaw]

A kitchen oven will not get hot enough.  One problem with tempering springs is that the draw temperature depends on the steel.  Most springs in our locks are 1095 but TRS springs are 5160 and the draw temperatures are different.  1095 springs do well drawn to 750 but 5160 springs draw at 700.  In the absence of a thermometer for your lead pot you can do the following:  polish the hardened spring so the surface is clean and bright.  Put the spring on a piece of steel about 1/16" thick that is larger than the spring aligning the springs so as much of the spring as possible is in contact with the steel.  Heat the steel from below with propane torch with a wide tip, moving it around so that it heats evenly.  Carefully watch the color of the spring.  Just at the point where it goes from blue to steel gray, knock it off the steel into some quench oil.  When the spring is starting to color you can judge where you need to be heating the steel by watching the colors on the spring to keep them even.  Let the spring cool completely before compressing it.  Don't compress it completely the first time, kinda work it down and never let it snap open.

Tom

[Mark Horvat]

Bookie always recommends a tuna fish can with used motor oil.  Put the spring in the can and light it off.  After the oil has burnt off the spring will be properly tempered.  A little gunkly, but properly tempered.

Mark

[rich pierce]

Nobody can explain to me why the burn-off method works, but it does.  So frustrating when things work and I don't know why, lol.

[doug]

    I have made at least 50 mainsprings and always use drill rod which I presume to be 1095 steel.   Initially I used the molten lead method and judging the temperature by floating a piece of THIN steel or iron and watching for the colour to run just beyond dark blue then in with the spring and pull the plug on the pot.  later I changed to the burning oil method and it worked well on large springs but not so well on small sear springs and similar.  Currently I use an electric lead pot and a high temperature thermometer and draw the springs to 720 - 730 F   I was heating to about 680 but felt that the springs were too brittle.  At 720, none break and none appear to bend or lose their temper,

    On one very large mainspring I tried using a piece of car leaf spring.  Heated to 730 F it still broke (2 springs and 2 tries) and I suspect it may have to be heated up to 800 F or more or perhaps it just air cools to its temper.  Much easier to stick with drill rod and have predictable results

cheers Doug

[Randall Steffy]

I so appreciate knowing the exact temp. of the lead bath that I searched further for the armored, partial immersion 750 degeree thermometer I use. At Thomas Scientific for $67.32 or search for a better price.
Link to Thomas http://www.thomassci.com/Miscellaneous-Thermco/_/WITH-ARMORS-30/750-F?q=9321L40

[smallpatch]

OK, so here's what I understand.  Heat spring to red, and quench in tranny fluid.

Let it cool, put it in a tuna can with motor oil, light it on fire, and let it burn out.  Then the spring should be ready??

If I were to do it the scientific method, with a thermometer,  heat to 700 deg, and hold for how long?

[Bob Roller]

DRILL ROD!Melted lead and burning oil?? This is all but unbelieveable. For decades I have used 1075,annealed and sheared to width in  3/16,1/8 inch.3/32 and .030 thickness. I made a sine bar with two clamps to hold the spring blank at the proper angle and using a four flute carbide end mill,the taper is thus established for the lower limb of the mainspring. After the spring fully forged  and shaped,I then heat it to a dull red and set the pre-load of the upper and lower limbs. I let it cool,polish it,reheat to about 1400F and drop in in common motor oil. After it cools,using a magnet I get it out of the oil,wipe it dry and repolish it. Using a Bernz-o-matic torch with a special tip I made for the purpose,I watch the colors change while holding the spring by the stud that goes thru the lock plate. I use long handled duck bill pliers for this. This method absolutely works without all the flaming oils,hard to work materials and melted lead.
As stated earlier,I have locks all over the world that have springs made by this method and NO reported failures to date and on the mantle in the living room is a caplock I made in 1968 that survived a fire that destroyed the rest of the rifle but the springs still have some life in them and eventually,I will retemper them
and restore the rest of the lock. I have used this method for about fifty years and success is its own story.

Bob Roller

[smart dog]

Nobody can explain to me why the burn-off method works, but it does.  So frustrating when things work and I don't know why, lol.

Hi Rich,
I believe it works because the oil ignites at a specific temperature.  I don't remember if it is 700 or 750 degrees F.  The burning oil simply creates an oven around your spring at that temperature. Theoretically, it does nothing more than if you heated the spring to the same temp using some other method like a burn-out oven.  I assume that if you don't force-feed oxygen to the burning oil, it will remain at that temp while burning.  I use 1075 steel for my springs and found the burning oil sometimes resulted in adequate but mushy springs.  I use my burn-out oven now and can control hardening and tempering very precisely to get exactly the spring characteristics that I want for the particular job.

dave

[doug]

     main reason that I stopped using burning oil was that it was a nuisance when it was raining or blowing and fresh oil is difficult to keep burning.  Old lube oil with lots of crud in it seems to burn OK.

cheers Doug

[bgf]

Nobody can explain to me why the burn-off method works, but it does.  So frustrating when things work and I don't know why, lol.

Hi Rich,
I believe it works because the oil ignites at a specific temperature.  I don't remember if it is 700 or 750 degrees F.  The burning oil simply creates an oven around your spring at that temperature. Theoretically, it does nothing more than if you heated the spring to the same temp using some other method like a burn-out oven.  I assume that if you don't force-feed oxygen to the burning oil, it will remain at that temp while burning.  I use 1075 steel for my springs and found the burning oil sometimes resulted in adequate but mushy springs.  I use my burn-out oven now and can control hardening and tempering very precisely to get exactly the spring characteristics that I want for the particular job.

dave

I think the hardening step may be more important than the tempering step in some ways in the case of mushy springs.  Do you control your quench temperature somehow also?

[keweenaw]

Drill rod, the oil tempering kind, is O1 not 1095.  rC50, the standard spring temper, is achieved with O1 at 800 for an hour.  My father made hundreds of Vee springs in his 65 years of gunsmithing in central Pennsylvania.  All were tempered by color and eye.  The local skeet shooters found that the springs in their expensive perrazi's broke at about 20,000 cycles.  Some of Dad's hand made springs had gone through more than 150,000 cycles the last he heard.  None had broken.

Tom

[smart dog]

I think the hardening step may be more important than the tempering step in some ways in the case of mushy springs.  Do you control your quench temperature somehow also?
[/quote]

Hi bgf,
Nope, it was the tempering step.  The springs were very hard before tempering. My quench is always at room temp (which obviously varies a little) and consists of a thin layer of oil over water.  When I say mushy, I don't mean they no longer are springy.  They simply are not as strong as I wanted.  The tempering was simply too hot using the oil.  Now, I don't worry about any of this stuff because I use the burn-out oven, which is programmable.  I can make springs with any characteristics that I want.

dave

[smallpatch]

How long do you hold the tempering temperature before the spring is ready???

[Acer Saccharum]

I think the strength of a spring is based upon the material thickness, not the hardness.

If tempered too much, it won't return properly, and take a set. Not tempered enough, and it will break.

You can try heating it up, spreading the arms, and then rehardening and tempering. But you may find you need more material on the leaves.

[Frank Barker]

I believe if I were going to temper a spring for one of my locks I would go with Mr Bob Roller's method. After all, he has made some of the best locks that have ever been built around these parts. I have had three guns with Roller locks and triggers and they are the quickest firing locks I have ever seen. If I were building a rifle today and I could get a set of Bob's lock and triggers I wouldn't  hesitate putting them on one of my guns. Thanks Bob for the info and I hope you are doing well..    Frank

[Dphariss]

I think the strength of a spring is based upon the material thickness, not the hardness.

If tempered too much, it won't return properly, and take a set. Not tempered enough, and it will break.

You can try heating it up, spreading the arms, and then rehardening and tempering. But you may find you need more material on the leaves.

This is not the case.
The old light weight springs are generally far stronger than modern springs with much heavier leaves.
It has to be the temper. I changed all my Shilohs to Spencer mainsprings (same internal lockwoork) for this reason. The  Civil War surplus (?) springs are stronger and faster than any modern spring. But probably weigh 2/3s maybe 3/4  what the modern reproductions do.

Dan

[Bob Roller]

Frank Barker.
Many thanks for the kind words and endorsement of my locks and triggers.
So far so good as far as my health is concerned.
I celebrated my 75th birthday last March and don't feel any different than I did on my 50th.
Shop work is good and I am now more selective iin what I do as far as lock work is concerned. My current project is 10 Twigg flintlocks and I am now on #7 of that group. I have not made up my mind to make any more because at $300 apiece it certainly won't be a "hot item".
IF there is any more interest, I may make a second group but I will need orders for at least 10 before I will consider doing it,
Thanks again.

Bob Roller

[Dan Fruth]

I hope you will list the Twiggs on here, as I might be interested. At $300 per lock for a scratch lock, that is a bargain. By the way, I make springs from 1080 bar stock, purchased from Admiral steel. at 1/4" thick. I don't use any special equiptment for tempering than polish the spring, and SLOWLY heat with a mapp gas torch till the colors start to show. I take it to the last color, a bit past purple to the gray-black color and quench in transmission oil. They always turn out fine. Of course, It took a couple of broken springs at the wrong temper color till I found the right color to quench at. I suggest if you try this method, make some strips of the same steel, and temper each at the purple, purple with black spots, and grey black color range to see which is right fot the steel you are using.

[Don Getz]

Bob...........so good to see you responding here .   I've always admired your locks, looking at the back side always reminded me of a good watch.   Son John has two of your locks, is keeping them for some little southern mtn. rifles he
would like to build.   I am 78 years old, but still enjoy gun building, but I will admit that my work day is getting shorter.
I have never fooled with main springs on locks, have always used them as I got them, mostly Siler locks from Jim Chambers...............Don