Pocket Knife Spring Tempering

[Gene Chapman]

There is mucho info on blade tempering and how hard the edge should be depending upon how the blade is to be used.

BUT

The info on spring tempering doesn't seem to be as abundant.

I temper my folder springs by heating till the quench oil burns off the spring, with the spring away from the forge, do this three times, the theory is the heat from the buring oil is about 700-900 degrees F. This is an old blacksmith method described in various ways, most notably "Practical Blacksmithing by MT Richardson, originally published around 1889. The heat treat chart I posted earlier would put the expected hardness of 700-900 degrees F at about RC 44-51 from the burning oil.



In the "Pocketknife Manual", by Blackie Collins, a interview with then Imperial founder Felix Mirando, Mr Mirando describes heat treating 1095 for blades and springs, in short the springs are tempered for a hardness of 46-48, (I think he is refering to Rockwell C scale).

Found this on the web today
http://www.engineeringfindings.com/cat22/cat22pg66.pdf

Just rambling here and thinking about spring tempering when I should be painting the trim on the house.

[Mongoose]

The method I use was taught to me by a fellow who has been making switchblades since the 60's, very similar to yours, Gene.

I don't use anything but 1095 now. Oil quench harden then lightly sand to see the steel. 'Paint' it blue with a torch and let air cool, then repeat the sanding and blueing twice more. Haven't had one break yet... and they get alot of use.

[Dana Acker]

One of those cool old timers who just seem to know everything, told me he tempered his springs by first heating it to critical and quenching it in oil so that it was "glass hard." He then placed the spring in a pot of molten lead. He said the temp of molten lead was perfect for tempering springs--these were for clock springs. Oh by the way, this cool old timer also told me that he learned his technique when he was a young man from another cool old timer from days gone by, so it's an older method, to be sure.

[Dana Acker]

So Gene, let me see if I read you right, do you quench your springs 3 times and burn the oil off each time? Or do you quench once, then dunk it in oil the other two times you burn it off?

[Gene Chapman]

Thanks for the inputs, Dana I quench once then burn off the oil, redip, burn , dip three times. Whatever hardness it gets to it can usually be filed and drilled and even bent a bit for the final fit. If one is still a bit hard for drilling I sand all the burnt oil off, rinse in acetone then ust a torch to color temper to about 700 degrees.

I suppose a small electric kiln with a accurate controller would be good for knifemakers but I have always used color tempering or the oil thing and have good results. If it works, don't broke it.

[Gene Chapman]

The only tool I use as quenched is a scribe. The sharpened tip is heated with a torch, about 1/4" of it then repidly quenched in a piece of beeswax. It's so hard it will almost mark a file but brittle, only use it for marking metal.

Making tools is fun.