doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Making Springs

Got some spring stock from Dixie Gun Works for a toplever spring. Took a long time to cut, grind and file to shape. However, the heat treatment proved most tricky. Heated till strong red, held at that temp for about a minute, then dunked in oil. Brought it back to dull red in a dark room. It was too soft. Repeated. Brought it back til the bright blue just turned silver in the light. Still too soft. Now I was nervous my spring was going to fatigue. Did the hardening again, maybe a little hotter and longer (orange red) before dunking. Brought it back to dark blue through gray with the non-working arm still purple/brown(wasn't able to get uniform color with a torch and didn't want to overdo it). This time it had good spring temper. Hopefully it will last.

Anyone have advice for making springs?

Mr. dghq:

As you know, hardening a spring is a simple matter of heating it above the upper critical temperature and quenching it. Tempering, now there's the rub. There are two ways to approach it, one is art and the other science, both work fine.

Heating to the proper oxidation color or putting it in a tin of oil and burning the oil and a few other methods I have heard of are art. Or alchemy. They work very well for those who have mastered the techniques through experiment and experience. I am in awe of that sort of skill.

The other way is science. You simply heat the hardened part up to the proper draw temperature for the steel, soak it at that temperature for a period of time and let it cool. The draw temperature is dependent on the alloy chosen, but for a spring steel will be typically in the neighborhood of 700 degrees F. This information is available in tables that specify the draw temperature required for a desired hardness for a specified steel.

There are a number of ways to heat to a specific temperature. A heat treating furnace would be nice. <g> Howsomever, if you happen to cast bullets you can use your electric lead pot and thermometer. Just get the lead to the right temp and soak the spring in it. Dipping the spring in oil before immersing in the lead will help keep from tinning it. I use a cheap Lee lead pot with Nitre Bluing salts in it the same way. No worries about tinning and the spring comes out real pretty. <g>

A precision electric hot plate will work well, but they ain't giving them away either. Perhaps the cheapest route would be a temperature indicating product like Temp-Lac or a Temp-Stick. These are compounds that melt a a very specific temperature. Put a mark on the spring and heat on an electric stove top until it melts, remove the spring and let it cool. A temp stick will cost about $10 from MSC or J&L. I suspect Brownells will have them as well.

My goodness, this got wordy...

Glenn

GF - nice description, well said.

All of what Glenn said plus the kitchen oven is also a possibility for tempering. Depending on the model, you may need the self-cleaning cycle to reach desired heat. Most have fairly accurate controls and all can be calibrated. Some wives may object - now there is a calibration challenge!!

Or, you can buy a top lever spring from Brownells. They have a variety of sizes and their tech. people can measure each one to help you come close to a match. I made one for my Lefever with the help of several people here and it works fine.

Before heat treating, be sure any scratches have been polished out, particularly any that run transversely to the long axis of the spring. This is to avoid large stress concentration, leading to fatigue failure.

There is an excellent tempering trick for top lever springs if you have access to an old supply of sperm oil (big if) and a torch. The flash point of sperm oil happens to coincide with the ideal tempering temperature for carbon spring steel. The hardened spring is dunked in oil and then heated evenly in the torch flame until the oil just begins to flash (ignite). The torch is played on the spring just enough to hold the spring at the flash point for 30 seconds or so and then allowed to air cool. The 'smith who taught me this trick had tried some synthetic lubricants, but the flash point was wrong. In his experience, it has to be the genuine whale stuff. It works for me.

I make 5 to 10 springs a year, mostly V shaped mainsprings. I forge them to approximate thickness out of 3/8" drill rod, and after final shaping etc, heat red hot and quench in water. My current method of drawing the temper is to immerse them in old lube oil in a small tin tray and supported by a couple of 1 1/2" finishing nails. I heat the oil, with a torch until it catches fire and let the oil burn away.
I am not really sure why the burning oil method works, because the flames are hotter than the temperature that I am drawing to, but the method works and works well.
I used to float the springs on molten lead in an electric lead pot with first a small thin piece of iron to measure colour and later with a lead thermometer and heat to 680 degrees F. The colour spectrum was the beginning of grey just beyond dark blue.

cheers Doug

I also use Dougs method for drawing - but when you first heat to critical use a magnet - when it won't stick to the heated metal it's time to quench . This is true for any carbon steel . Too hot , and the grain will grow making it weaker . Paul

Thanks guys, I have been doing some research. The oil trick has to do with the firing point (not flash point) of oil (the temp of the liquid at which it will flame unassisted). Using this method, temps of 650-700 are obtained, depending on the oil. Old used oil gives a temp much lower (circa 550)> Everything I have read says to quench in oil, not water. Water makes for a higher tensile strength but also higher risk of breakage. Suppose it depends on the steel you are using. I have seen recommended drawing temps for leaf springs from 550 to 800. Dixie says color should be bluegray for their "spring stock". That's about 740 I think. The lead trick is interesting. Apparently, you can vary the melting point quite a bit by playing with the tin/lead mix. 4% melts at 560 deg, 8% at 550. That corresponds to dark purple and full blue, both a little cool for spring tempering. Of course, you can heat the lead to temps much higher than this but you need a pyrometer to know where you are.