mainspring for double set trigger

[eagle24]

I am to the point of making springs for a couple of double set triggers I have made.  I was going to make the mainsprings from O-1 Tool Steel.  I can cut them out and file them to the proper curved shape or forge them.  Is either method OK?  Can I simply harden the O-1 and then temper it by burning a pan of oil with the spring in it?

[Elnathan]

I don't think O-1 will make proper springs. It makes wonderful chisels and smaller knives, but I know that it is not favored for larger knives because it does not have enough springiness to keep the blade from snapping under heavy use. Knives and springs are tempered differently, of course, but O-1 has a fairly high carbon content (1.0 %) as well as added elements like chromium that make it unsuited for springs, I think. You might be able to make it work, but I suspect that it would be difficult. A better choice would be a steel like 1075 or 1095, which are classified as spring steels.

[smylee grouch]

I have had some succes using old flat spring (anneled), cutting,shaping.hardning and tempering by placing spring into a lead pot and holding there for about a min. This has worked for me in the past.   Gary

[Jim Kibler]

There's nothing wrong with O1 for springs.  Forge or machine to shape.  Either will work.  The only difficulty is that you will have to temper at a much higher temperature than that commonly used for lower carbon steels used for springs.  With a fully hard structure after quench, a tempering temper of 950-1000 F should probably be used.  This will likely yield a hardness in the mid to lower 40's on the Rockwell scale.  The difficulty lies in knowing when the spring is at the 950-1000F if you don't have a heat treat furnace.  At the higher temering temperatures you run out of temper colors to aid in judging temperature if using a torch or similar heat source.

[eagle24]

There's nothing wrong with O1 for springs.  Forge or machine to shape.  Either will work.  The only difficulty is that you will have to temper at a much higher temperature than that commonly used for lower carbon steels used for springs.  With a fully hard structure after quench, a tempering temper of 950-1000 F should probably be used.  This will likely yield a hardness in the mid to lower 40's on the Rockwell scale.  The difficulty lies in knowing when the spring is at the 950-1000F if you don't have a heat treat furnace.  At the higher temering temperatures you run out of temper colors to aid in judging temperature if using a torch or similar heat source.

So if I used the O-1, I can't burn it off in a pan of oil to temper?  not hot enough?  For a trigger mainspring will it be that critical since it doesn't bend much?

[Jim Kibler]

You're right in the fact that a set trigger spring isn't as highly stressed as a lock mainspring.  It will be more forgiving and likely could tolerated a higher hardness without failure.  There is still a significant difference in tempering temperature resulting from the oil burn off and the temperature I previously suggested.  My guess is the oil burn would put you somewhere in the range of 650 F or maybe a little more.  That's a long ways from 950 - 1000F.  Look up a tempering curve for O1 steel and see what a 650 - 700F temper will put you at.  I'm sure it will be well over 50 HRC.  Pretty hard for any spring.

[eagle24]

Thanks Jim.  I think I will order some steel better suited and that I can temper at a lower temp.  Sounds like it will be easier for me to control the finished spring.

[Benedict]

Wouldn't tempering in a molten lead bath get the O-1 spring closer to the correct temperature as someone mentioned?  It might be worth a try before spending the money and time to get a different steel.

Good Luck

Bruce

[keweenaw]

O-1 makes great springs. The recommended temperature to draw O-1 to Rc50 is 800 degrees for one hour if you're using a furnace.  You can draw a simple spring like this by eye.  After hardening it, polish it back to bright, put it on a piece of steel and heat from underneath until it goes past blue to steel gray color. At that color knock it off the steel into the oil again.  It will be close enough to the correct hardness to work in your application which is not nearly as critical as a V spring. The set trigger mainspring in my chunk gun was made from O-1 exactly this way. I would be inclined to simply file/grind it out rather than trying to forge it as you might have some difficulty in drilling and tapping your hole if it cools too rapidly off the forge and you need to have it quite hot to forge successfully.

Tom

[Jim Kibler]

I agree about a set trigger spring being pretty forgiving.  Just a note...  Blue temper colors turn to light gray at around 640F.  From 640F to the suggested 800F, it's pretty iffy to judge temperature by color.  You can just sort of guess on temperature and with the spring being fairly forgiving, you may likely get away with it.  I'd give it a try.

[Dphariss]

I am to the point of making springs for a couple of double set triggers I have made.  I was going to make the mainsprings from O-1 Tool Steel.  I can cut them out and file them to the proper curved shape or forge them.  Is either method OK?  Can I simply harden the O-1 and then temper it by burning a pan of oil with the spring in it?

O1 makes great springs and it has a somewhat wider quench temp than some steels. Filing or forging will work though I think its harder to forge than plain carbon steel.
I don't do the "burn off oil thing" to temper. I like to do substantial springs in molten saltpeter. The heat bluing/Nitre bluing salt that Brownells sells is saltpeter. I made a small long tank years ago out of a piece of conduit and used to buy the salt at the drug store . That works for pieces up to a large mainspring. The saltpeter remaining on the spring dissolves in water leaving a nice blue spring. Always heat the sides of the container first to allow oxygen to escape.
It allows watching the color of the spring and heating the thin areas slower if done right. I seldom loose a spring this way.
If you forge O1 heat the entire piece of metal leaving an end cold may result in a break since the cold end may "quench" the hot-cold border and the piece will break at that point when forging.

Dan

[P.W.Berkuta]

GHall -- if you want a small piece of either 1075 (annealed) or 1084 (not annealed - as rolled) send me your address and I'll send you a 1/2" X 3" or so piece. e-mail me at <  pberkuta@earthlink.net  >