View Full Version : Re-tempering coil springs?
11-29-2009, 12:17 PM
I have a bipod spring that is too weak to keep the bipod legs open.
I've read that you can heat treat the metal to return its spring properties, but I'm not sure how to proceed. Does anyone know how to re-temper a spring? I searched "temper coil spring" and found a reprint of a really old book online that talks about dunking the spring in mercury, wax, and all sorts of other old-time solutions, but it doesn't really spell it out in a way I can understand.
I'm thinking I can heat it with a propane torch to a certain redness then quench in either oil or salt water to obtain a temper?
11-29-2009, 12:59 PM
Works the same as hardening the pivot pin holes on an AK receiver. Cherry red, dunk it. Draw it back out to blue. Done.
That said, if the spring isn't working now, chances are it won't after re-hardening unless proper steel was used with improper hardening in the first place. I've seen a lot of cheap chrome "springs" that weren't worth spit.
Also, each heating drives out some of the carbon necessary to the steel's spring properties. You can reach a point where all you have is mild junk steel.
11-29-2009, 09:30 PM
I've tempered a whole lot of flat and "V" springs in my day, but when the coil springs were needed I either selected a similar one from my collection and cut it to length, or wound my own from music wire. I always figured the thin metal would A: melt too easily and B: not retain the heat long enough to be quenched. Music wire is already the proper spring temper.
Music Wire - Supplies - Hardware - Grainger Industrial Supply (http://www.grainger.com/Grainger/music-wire/supplies/hardware/ecatalog/N-9bz?op=search)
For tempering a flat spring, you heat to the glowing red critical temp and quench just like heat treating a receiver. Hard and brittle, you then draw it back at around 700 degrees. I always dunked it under the molten lead in my Lee lead melter for about 5 minutes, molten lead is about the correct temp. Never had one not be a spring when I was done.
11-30-2009, 01:28 AM
Many automotive supply stores sell bags of assorted springs. If none seems to be close to your needs measure the wire size of the existing spring and get a 3 ft length of that music wire at a local hobby shop. Then wind that around an undersized mandrel. A vise helps holding in this winding.