Tempering Spring Stock

[pflyman]

I am making the patchbox spring for a 1792 contract rifle.  I was provided a 2" piece of spring stock.  I bent it to shape and inletted it.   I searched the archives of this forum to learn how to temper the spring.   I found several methods.   I utilized one that recommended "normalize", "quench" in oil, and "draw" in molten lead.   I don't have a thermometer so I melted lead shot in a cast iron pan over a single burner camp stove.   I attempted to immerse the spring but it continued to float.   I kept it in this bath for 20 - 30 minutes.  When finished, the piece was still bendable and did not retain its shape.  What did I do wrong or is there another technique I could use?

[George F.]

I have had trouble tempering springs myself. After you are satisfied with the shape of the spring, you need to harden it. just like a frizzen. Heat it to bright cherry red, and quench it in transmission fluid. Then you need to temper the spring. I use a nitrate salt bath with a thermometer. I heat the bath to 700 degrees F. The trouble with using the lead is you can over heat it, just like the salt bath. So I'd get a thermometer. Oh, the steel will float... it's lighter than lead.  ...Geo.

[Dphariss]

Even when I use saltpeter I still go by color. I do small springs with a torch.
When it reaches a nice blue or just past (grey blue color maybe) I remove the part and allow it to air cool.
Its just as important to not overheat before quenching.
Dan

[rich pierce]

I don't have a thermometer.  As soon as the lead melts I cut back on the heat and keep checking how it pours from a dipper used to cast balls.  I let the pot stabilize to "just liquid".  I immerse springs by wrapping with plain black iron wire and push it down in.

[pflyman]

Thank you all but I am still unclear how to proceed.  If the thermometer is necessary, what is a typical source for a thermometer of this range?  I have no information on the use of saltpeter so I would prefer to use lead.  How long do you leave it in the lead?

[J Shingler]

Lay it on the lead and when it melts you are there for a small spring. I would push it under just a bit to make sure it is equalized.  Check it with a file after your quench to make sure you got it hard in the first place.
Jeff

[Pete G.]

I use spring stock from a lawn mower recoil starter for these types of springs. Of course it is hard to begin with so I have to heat it to form it, but then reheat to a cherry red, quench in a light oil, then polish back to bare metal. This time I hold it out past the end of the flame on my propane torch and keep it constanly moving. As soon as it turns a light yellow I quit. Generally there is enough residual heat that the spring will color to a light blue at this point. Let it sit and cool to the touch and it should be good to go.

[jim meili]

I have made dozens of springs and draw the lighter ones like your patch box spring by dipping in oil and burning the oil off. Hang spring on a wire and dip in 10W motor oil, dripping. Light the oil with your propane torch by passing the flame over the oil. Do not hold the part directly in the flame as you will over heat the spring and soften it. Let the oil flame and burn itself out. this should do the trick.

I do heavier springs in lead by setting them on the lead and heating the pot until the lead becomes liquid. Pull off the heat or unplug the pot and let everything cool down together. The part will float on top and just before the lead solidifys pull the spring out. I have never immersed a spring, it gets plenty of heat by just sitting there. If you must just put a cover of some kind over the pot while it cools down. To keep the lead from sticking to the spring coat it with a little soot from a candle or match. it will come out clean. The lead is at 620 or so when melted so there isn't much need to watch the color.

You can draw bigger springs like main and frizzen with the oil trick but you pretty much have to put them in little tin of oil and burn it all off to get the right heat all the way thru. If it's not tempered all the way thru you will be making another spring because they will break for sure. Bookie uses the oil method and has good luck. You can check his website for good instructions on how he does springs.

[doug]

Thank you all but I am still unclear how to proceed.  If the thermometer is necessary, what is a typical source for a thermometer of this range?  I have no information on the use of saltpeter so I would prefer to use lead.  How long do you leave it in the lead?

     I make 5 or 10 mainsprings a year.  I draw the temper with the spring on edge in a tray of burning automotive lube oil.  When the oil is gone you have a spring.  It is a very dependable method for me.
     If you are using molten lead, float a thin piece of clean bright iron or steel on the lead.  As the lead melts and heats up, watch the colours in the steel.  When the steel hits the transition from dark blue to grey, remove the heat source and float the spring on the lead almost until the lead has cooled to the crystalizing stage.
     If you have access to a high temp thermometer and an electric lead pot, heat the lead to 680 F and pull the plug and of course quench the spring.

cheers Doug

[Jim Kibler]

One thing to keep in mind when tempering springs is the material it is made out of.  For example, an ideal tempering temperature for 1060 (approx. 0.60% carbon) is going to be different than that for 1095 (approx. 0.95% carbon).   With this being the case, tempering methods such as buring oil or a melted lead bath might work well with one material but not another. 

[Dphariss]

Thank you all but I am still unclear how to proceed.  If the thermometer is necessary, what is a typical source for a thermometer of this range?  I have no information on the use of saltpeter so I would prefer to use lead.  How long do you leave it in the lead?

If you use saltpeter you can use a container just large enough to get the spring into.
When the cold spring is put it it will freeze a shell of saltpeter on it and as it heats this will melt off. Put the heavy in end in first to give it a little more soak time. Spring must be completely degreased and dry. Water or other liquid in heated material can produce an explosion just like lead. Oil will burn off but you get little color.
As the stuff melts off you can watch the color removing the part as needed to see well or take out the thin areas and leaving the heavy in as needed. I generally take it out just as it starts to loose its bright blue color.
You can cut the top off a 6" section of 1.5" or so conduit and then braze on ends. Dip in acid to remove coating first.

Fill with SP and heat on the sides initially with a couple of propane torches. Heating the sides allows the oxygen being produced to excape with no pressure build up.
When melted keep the heat on and start the spring.
If you cut the heat back too much at this point it will start to solidify but experience will help you adjust the heat.
When the spring is a uniform blue remove and let cool. Wash with warm water to remove saltpeter.
This requires no thermometer and I seldom loose a spring made in this manner.  I have a broken MS on my tool box from back in the 90s and thats the last  spring I remember breaking.

This is much faster than starting up a lead pot and the spring is squeaky clean after washing.
Great way to heat blue any part as well Brownell's sells the stuff in large quantity and a larger tank will allow blueing bigger parts. A stainless kitchen ladle from Walmart makes a great "pot" to heat blue case hardened screws if you have a large batch 5-10 to do.

Dan

[jerrywh]

I want to say that the bluing salts that Brownells sells is not potassium nitrate,  It is sodium nitrate. The difference is , sodium nitrate melts at a much lower temp then potassium nitrate. The lower melting point allows for much more control of the temperature.
Potassium nitrate does not work near as well as sodium nitrate. If you use potassium nitrate you may experience some problems because of the higher melting point.

[keweenaw]

For a single, not critical spring, most of the suggestions are way more complicated than they need to be.  Heat to cherry red, quench in oil -  linseed oil or transmission fluid will work.  Polish one side of it until you get clean metal.  Put it on a flat piece of steel about 1/16" thick .  Using good light heat the steel you have the spring on from underneath with your propane torch until  the color of the spring just goes past blue to a pale gray and drop it back in the oil.  When it cools you'll have a spring.  The alternative, long time used, simple minded tempering technique is to make a dent in the side of a metal can big enough to hold the spring.  Put the spring in the dent and pour on enough motor oil to cover.  Light the motor oil and let it burn off.  When cool you'll again have a spring.  Don't make it complicated because it need not be. 

Tom