Spring Temper Followup

[Erzulis boat]

This is the followup post to my previous spring questions.

I had some rather substantial mainsprings to harden/temper and was wondering about getting a thorough enough temper "soak" so that the spring would be durable and would get evenly tempered.

The steel is 6150, and these are TRS castings. Everything worked perfectly, and this is how I did it. Remember, this worked for me, but there are other ways to do this.

TRS (The Rifle Shoppe) said that I was to heat to 1525F (+-) and do a water quench. The heat source could be propane, and TRS said that propane was preferred, as the color was easier to see (metal color for heat estimation).

Tried propane and couldn't get the 1500's (temp) even as the torch required to much lingering time, and then a "cold" spot would appear.

The springs that I had done previously had all been done with straight acetylene, but they were not so thick and large as the Snaphaunce mainspring.

Went to oxy/acetylene and had nice even heat without any fuss. You will note the temperature senstive "crayons" in the picture, and these were used to get the temperature dialed in. I did not want one of these mainsprings to fail in the lock mortise!

Water quench was a No-Go, I could plainly see small cracks, some with the grain of the casting, and some not. Those springs were discarded.

Went to my old Linseed bucket that I have used for 3 years now...............perfect. The parts were not "glass hard", I could scratch them with a new sharp file. I have got some springs glass hard, but these TRS castings never got that way even with a water quench. ???

No big deal, every steel alloy does it's own thing to a degree (no pun intended).

I broke out the propane for the tempering operation, as the slower heat is actually very nice. Oxy/acetylene burns very bright (UV rays) and getting an accurate color estimation is difficult when you go sub 1500's (glowing).

I got the parts to go through blue, then through the spectrum again until I had the slate grey. I hit it with the "crayon" and got the melt. I then just very lightly washed the propane flame over the entire spring with constant movement and kept it running slate grey (850-875) for a five minute period. I then dunked the mainsprings in linseed.

Both springs worked perfectly! I was pretty worried about the thickness, but I just took her easy, and everything came out fine.

The smaller springs like the frizzen and the internals (you should heat treat the internals on these big locks, the spring pressures will just roast the surfaces unless the tumbler/sear is hardened too) were done the same way and likewise came out great.

Anyway.......enough yapping. With oxy/acetylene, propane, and linseed you can do the very largest mainsprings from TRS.

Andrew B.