Temper for crossbow arms

D

DSTY

Joined
Mar 8, 2023
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Hello. I know this isn't technically about blades, but about something that slings them. I have old leaf springs and they're about the right size to make crossbow arms.

The issue is that I know I need to cut them in order to make the arms usable, but what I don't know is if I need to re-heat treat them, or even quench them after I'm done. How should I heat treat them to maximize the yield stress, or springiness?
 
DSTY said:
Hello. I know this isn't technically about blades, but about something that slings them. I have old leaf springs and they're about the right size to make crossbow arms.

The issue is that I know I need to cut them in order to make the arms usable, but what I don't know is if I need to re-heat treat them, or even quench them after I'm done. How should I heat treat them to maximize the yield stress, or springiness?
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If they just need shaping, you can do that on a bandsaw with a bimetal blade, and you can grind them as long as you cool them with water. This would require no heat treating at all.
 
It is a lot of work to cut and grind down a leaf spring to make a cross bow arm, but it can be done depending on your equipment. A better choice is to get a bar of 5160 (or similar spring steel) and do all the work in the annealed state. After shaping you can set the curves and then do the HT (or have it done by someone else). This will make a more reliable bow. You will find that the steel does not need to be very thick to be powerful. IIRC, the last one I made I used 1/8" thick 5160.

BTW, the amount of force needed to bend the bow is the same hardened or not, so you can check the draw while fitting the bow before hardening. What changes is the yield point where it would take a permanent bend (annealed) or break (hardened). Breaking isn't normally a worry unless there is a problem with the bow steel. Used leaf springs may have microcracks and stresses that can break later on, so that is another good reason for using new and known steel.
 
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