6150 spring steel

[okawbow]

Trying to assemble a lock kit. The springs are cast from 6150 steel. I heat treated them by setting the springs on a steel plate on a gas burner and getting them to yellow/orange heat with a mapp gas torch and holding at that color for 10 minutes. I then dunked each piece in cannola oil and swirled until cool. I polished the springs and set them in lead that was barely melted for 30 minutes. The sear spring seems strong and does not take a set. The mainspring took about a 1/8” set right away and seems too weak now.

What am I doing wrong?

[rich pierce]

Have you looked for a crack or defect in the casting?

I think it’s possible you may have overheated when hardening.

[Bob Roller]

Cast mainsprings  I know nothing about but the one you show is made for a linked tumbler so reheat it and open the long lower limb down farther and repeat your heat treating procedure.That is called "PREloading and I have done a LOT of them but in 1075 made from strips.
Bob Roller

[okawbow]

Have you looked for a crack or defect in the casting?

I think it’s possible you may have overheated when hardening.

Doesn’t seem to be cracked, but I don’t think it hardened properly. Chris Hirsh says to quench in water. I was advised not to do that as it would be too brittle. I guess I will try the water. Maybe try a 500 degree oven instead of lead.

[okawbow]

Cast mainsprings  I know nothing about but the one you show is made for a linked tumbler so reheat it and open the long lower limb down farther and repeat your heat treating procedure.That is called "PREloading and I have done a LOT of them but in 1075 made from stripd.
Bob Roller

Thanks Bob, I’ll heat and re-shape the spring before heat treatment.

[smart dog]

Hi,
Don't quench in oil.  Use brine at room temperature or even about 100-120 degrees.  I have a half gallon pail of warm water mixed with about 1 cup of Kosher salt.  I find that TRS springs and those from India-made guns harden much better when quenched in brine.  I don't bother with the steel plate.  I just make a little furnace with fire brick and heat the spring with a MAPP gas torch.  I do one at a time. I temper them at 750 degrees for one hour to be safe but 30 minutes should work.

dave

[bobw]

At 500 the spring will probably break when tested.
Bob

[rich pierce]

At 500 the spring will probably break when tested.
Bob

Agree, no hope for long term viability in my limited experience.

[okawbow]

Thanks, I’ll try the brine and 750 temper.

[Scota4570]

I draw to 750 in lead with a thermometer. 

[okawbow]

I decided to drill the tumbler for the hammer screw and fix the fly before doing anything else to the springs. After assembling the lock, I decided the main spring mounting hole was too low. I centered it on the lock plate and now the lock functions ok. The spring is not as strong as I would like, but the hammer fall is pretty snappy and the sear clicks into place nicely. I think  I will wait and see how well it shoots first. It doesn’t have to be as strong as a flintlock spring anyway.

[Daryl]

Slow, weak spring just increases lock time  is all.

[Jim Kibler]

If you put more arch on the lower limb, you might be able to avoid some of that backwards bend at full cock.  Ideally this ought to be straight of course.

[bpd303]

I think it wasn't heated enough if the color is correct on my monitor. I always heat to yellow (non magnetic) then quench and temper in molten lead in my lead pot at 700-750 degrees F. Never had one fail and the lock is fast.

[okawbow]

If you put more arch on the lower limb, you might be able to avoid some of that backwards bend at full cock.  Ideally this ought to be straight of course.

That’s the plan when I re-heat treat. However; this is a really skinny lock and not much room to place the spring. If I put more pre load in, I-might be able to file a little off the top piece that touches the bolster to get the lower arm lined up better.

[okawbow]

I think it wasn't heated enough if the color is correct on my monitor. I always heat to yellow (non magnetic) then quench and temper in molten lead in my lead pot at 700-750 degrees F. Never had one fail and the lock is fast.

How long do you hold at yellow heat before quenching?

[bpd303]

Just until it is nonmagnetic. Oh and I usually quench in warm peanut oil.

[okawbow]

Re-shaping and re-heat treating the mainspring seems to have worked. I bent the lower arm down a little and files the bump on the top of the spring a little. That allowed the spring to be brought to full cock without over bending. It’s also much stronger and faster.

Thanks for the help, everyone!

[okawbow]

Lock is in and functions great.

[Bob Roller]

Making springs that can be used is a trade/skill of its own.I can't remember how may requests I got to make new mainsprings for locks made by other makers but making them for my own locks was all I wanted to get done.I have a small "4 pin"about 3/4 finished I started 5 years ago that has a small "glitch in the full cock notch so I won't finish the main and sear spring until it feels like I want it to on full cock.
Bob Roller