Spring forming question

I have some spring stock from brownells. I need to make a flat spring.
So after shaping the material, what do I need to do to treat it?
Thanks Ed

Brownell's has a three part spring making video that should be of some help.

I sat through the first video and was not impressed.

You need to harden the spring by heating it to a dull red and quenching in oil. The old blacksmith's rule of thumb is to heat it to the temperature that will harden it to where a file doesn't cut it. At that point it will be very brittle so don't flex it. Next you need to temper it. Polish the scale off it and heat it until it turns a deep sky blue. I did a batch of springs that way, tempering them in an oven with a viewport and a thermocouple reading the temperature of an aluminum plate holding the parts and was surprised at how accurately the color indicated the temperature.

BTW, the melting point of aluminum is higher than the tempering temperature but don't use one for the initial hardening because it will melt first. I used aluminum instead of steel for better heat distribution.

This is a quick rundown. There is a lot of information on the net.

Bill

I have made flat springs / mainsprings for years for older guns and muzzleloaders. I'll give the way that I learned from two master muzzleloader builders longer ago than I want to think about. LOL

Shape the spring to size and shape. Place spring on a piece of firebrick and heat around the spring until the spring is full red.
Have a qt. jar full of mineral oil near by for the quench. When the spring reaches red, I use an old pair of needle nose pliers with prewarmed tips to quickly dunk the spring in the mineral oil and stir it for a few minutes. Don't just dip it but be sure to stir it while fully covered. This will harden the spring and leave it brittle. Do not try to bend it at this point.
To temper, I place the hard spring on its side in an old shoe polish can and fill the can with mineral oil until the spring is a little over covered. Set the can with oil and spring on the firebrick. Using a handheld propane torch, heat the brick, oil, and can until the oil ignites. Keep playing the torch on the oil and brick to keep the oil burning well for about half the oil then let the oil burn on its own until it burns out. Let the spring rest until cool on its own.
I have never had one break doing it this way. If you over heat on the temper, all you have to do is reharden and retemper.
This is not a scientific way but, an old way that still works and it works well using the spring stock that Brownell's sales.

BobbyBailey said:

Place spring on a piece of firebrick and heat around the spring until the spring is red ( duller red inside where it is darker, brighter red if outside on a sunny day ).

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I think you have this backwards. It will look brighter in the dark at the same temperature.

Bill

Bill, you are right. In my effort to give more complete instructions of what I do, I had a brain fart.

I've made a bunch of flat & V-springs for old guns. I agree with most of the above, except that when I temper a spring, I use nitre blueing salts.

I heat the salts to 575 degrees F, and dunk the spring in for several minutes. You should come out with a deep blue color. I like tempering in nitre salts because I get a very uniform tempering. You could also use a burn-out oven, but that will take more time.

Also, I polish the spring steel lengthwise. I tend to taper my springs both in width and thickness, so as to get the force to be spread across the spring's length, rather than concentrated in a small area of the spring.

Old time gunsmiths used to prefer to quench in Sperm Whale oil, and then use Sperm Whale oil to temper (per Bobby's instructions of using a snuff can of oil above) but that oil is now rather difficult to find.

Wasn't modern automatic transmission fluid created as a synthetic replacement for Sperm Oil?

I have had good luck making springs by annealing the material and forging or filing and bending to shape and then wrapping with iron binding wire. Heat it all to cherry red and quench in oil. I've used both used motor oil and vegetable oil with good results. Remove the piece from the quench and ignite the oil that clings to the wire wrapped part and let it burn off on its own without additional torch flame. When the flame goes out you can quench it again to arrest any further tempering. Cut the wire wrap off and you either have a spring or you don't. I think the process is written in the Brownells catalog.

A magnet gives accurate critical point and a nitrate or lead bath accurate tempering.Both heating and cooling are also time dependant.never place a cold spring direct into tempering bath.....incidentally the best result I have had with springs was when a friend was able to put them on the mesh belt of the furnace at the spring works where he was night shift furnace minder.In one side ,and out the other...Must be the same kind of steel that the process is setup for.

GGaskill said:

Wasn't modern automatic transmission fluid created as a synthetic replacement for Sperm Oil?

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Absolutely.

As far as spring making I have made dozens by simply heating the already shaped AND POLISHED spring stock to a nice red. Hold it there a minute or so, then IMMEDIATELY quench it in oil (I use motor oil), moving it up and down so bubbles cant remain in one place and allow a slow quench there. Take it out, remove the scale and polish it out again, then I hold it above, not in, the propane flame, moving it in and out to SLOWLY heat it to blue. A typical spring say 1 or 1 1/2" long I'll play the heat over taking maybe 5 minutes to get it to blue, I go that slow. The color progression will continue after you remove it from the heat so it is a good idea to stop when the blue first has a hint of appearance, that way it will stop at full blue. Let it cool slowly...I actually back it away from the flame, holding it maybe 1 foot above it for a few minutes (I cup my hand and check the heat from the flame...if its too hot for me its too hot for the cool down phase). You just dont want to set it down on a cold steel surface. Don't be shy....just go ahead and do it. One of the things you have to learn by doing. After a few springs you will wonder why there is such a mystery about it, its actually easy. The reason I stressed polishing before heat treating is that you want all minor scratches out of the steel so a weak stress point will not arise there causing failure when you are using it. Radius all corners, sand down with sandpaper, then go finer and finer and make sure you cant see any scratches or even worse, nicks. Good luck.
On edit: if you slightly over shoot the blue it usually will still work for its intended purposes, try it out first, but stopping before the blue will often result in spring breakage.

The trouble with describing the proper heat for hardening and also tempering is that your description of dull red and mine of fullred are that we can not really descide either colour with those names and viewed in what light the best judge of the correct hardening tem is to check with a magnet when the steel is not attracted by the magnet that is the correct temp to quench no guesswork , for tempering get a couple of temple sticks do the tempering when youhave sent the wife out shopping and use the oven ..Rob