doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Infrared Thermometer for Nitre Bluing.

I'd doubt you'd really need a medium other than air in the kiln, but if you want to use one, try to have it as inert as possible. It may not matter a whole bunch, but you may not want possible contaminants in a color casing kiln.

Ken, as Damascus and Kutter said, it can be tough to heat a spring evenly if it is thick near one end or the vee, and thinner at the end of the limbs. Damascus suggested using the silver sand as a medium to get even heating and Kutter suggested heating the spring from below while it is laying on a heavy plate of steel. Either method will work, but as Damascus said, you need to bury the spring very shallow in the pan of sand so that you can rake it away to check temperature or color. When it is a deep blue or whatever temperature you desire, remove it from the heat and let it cool. The burning oil method has worked very well for me too. After hardening, you put the spring into a shallow pan of motor oil and heat it with a torch until it catches fire. Tuna fish or sardine cans make nice shallow disposable oil burning pans for small gun springs. You then let all the oil burn off and let it cool. For small thin springs, you can just dip it in oil and light the oil covered spring with a torch and let it burn off, and repeat this short burning process 3-4 times. The burning motor oil methods are smoky and messy and best done outside. The old German gunsmith who first showed me how to make a spring used the latter flashing method, and he was using sperm whale oil and still had several gallons of the stuff.

Here are a couple good articles on spring making, one using 1070-1075 spring steel, and the other on tempering cast spring steel. The parts about filing and polishing are very important because any marks going across the spring will make it more likely to break when compressed. Even roughness from surface rust will make a spring more likely to break, which is why it is a good idea to occasionally oil the torsion springs on your garage doors.

http://www.metalsmith.org/pub/mtlsmith/V21.2/Springs.htm

http://www.ctmuzzleloaders.com/ctml_experiments/tempering/tempering.html

In the first article, the guy talks about heating to the critical temperature instead of trying to judge "cherry red" under different light conditions. When steel reaches critical temperature, it loses all attraction to a magnet. I have not tried this, but it certainly makes sense.

Ken,
since you have an oven you might as well try drawing your spring in a salt bath. It is easy to do. A lead bath is also easy but the fumes are toxic and my kiln is much more consistent than using a torch to heat the lead bath. Multiple ways of getting it done but the kiln is quite easy.
Steve

After shaping a v spring for a drilling (several hours}and flame heating and oil quench and tempering by color and breaking the spring, as a slow learner I tried several more times. Back to the net. One Paragon kiln about $700. Four separate programs: 1. 1472F,2. 580 F , 3&4 for my wife who makes silver jewelry from silver clay (and other metals). Every spring works and so does the jewelry. BTW, the net has replaced Henry VIII and his methods. Way more selections than his six and no beheadings, just press delete.

Have not seen anyone mention an ordinary lead thermometer. Goodwill pot, niter fertilizer from the garden shop, LP gas burner. Submerge(suspend) larger springs at 700�F for 15-20 minutes after quench. Several mainsprings have not broke yet. Also works for nitre bluing. Oil burn works for smaller springs.
Chuck

It has been a number of years since I have made a spring, but made several in the past. All that I have knowledge of are still working. These were all heated (by color) with a propane torch & quenched to harden & then tempered by the oil burn off method. When possible I would suspend the spring on a piece of wire rather than holding it in pliers & concentrate the flame on the thicker areas & let the heat run to the thinner ones.

Worked well for me for the number of springs I needed to make with minimum expense for set up. Of course if one is making a lot of springs on a regular basis then a more sophisticated set-up would certainly be advisable.

Thanks again to everyone.

It looks like I'll try the Nitre bath to "Draw the Temper", I'll try that first since it'll pull "Double Duty" for Nitre Bluing as well. I'll pick up some "Stump Killer" at the store.

I have two smaller kilns, both picked up at auction for less than $20 bucks each, another $100 for a 240V digital controller.

Regards
Ken