If it's woodwork, I'm damned good. Metallurgy is out of my wheelhouse however. Anyone out there ever drew the temper out of a leaf mainspring and then re-tempered to a lower tension? Here's my problem; I have an antique large frame S&W revolver that needs work. The mainspring is too strong resulting in a very heavy trigger pull in double action and it's a pig to draw the hammer back for single action. My guesstimate is that the tension should be reduced by at least 30%. I could try attempting to reduce the mass by using diamond hones but any metal worker knows how easy it is to induce stress risers into a spring if you don't have the tooling and the knowledge. A major consideration is the fact that if any work is done badly or incorrectly and the mainspring fails, good luck in finding a replacement part for a 140 yr. + old pistol. Any input or suggestions would be most appreciated.
re-tensioning pistol leaf mainspring
- Thread starter LawrenceN
- Start date
I doubt that trying to change the temper is a solution. Traditional springs were hardened by oil quenching, then tempered by reheating to the appropriate lower temperature. Too low a temper heat, the piece snaps, too hot, it takes a set.
Thinning the spring would be the usual approach.
Is the spring the original, or a subsequent replacement? I wouldn't expect a factory spring to be so strong that operation of the firearm has been impaired for 140 years.
Thinning the spring would be the usual approach.
Is the spring the original, or a subsequent replacement? I wouldn't expect a factory spring to be so strong that operation of the firearm has been impaired for 140 years.
You're smart to be concerned over parts that old. Instead the proper idea would be to make a new spring. Either you doing it or someone that knows how. Doesn't need to be a gunsmith but it needs to be someone that has experience making springs to be sure of a good match.
Your idea of re-tempering is a non starter. It won't alter the shape. And if you over temper it then it's part way to being annealed and will actually more easily take up a new collapsed shape. Do not do that.
So first up you'll need a heat source to work with some tool steel to make a spring. You'll use this for both annealing any hard materials to work them and later to heat up the metal again to harden it. An option that is very low in cost and works super well, using it myself in fact, is a "soup can forge" using a swirl style propane torch for the heat source. Do a search on You Tube for "soup can forge". Hint, instead of all sand to go with the plaster of paris I went with 1/3 sand and 2/3 perlite. Better insulation properties. Does it help? Not sure but my simple forge works very nicely and heats up fast.
Next is to get some tool steel that can be hardened and tempered. Old dull files are one source. But of course there are a lot of other options too. If you use a file be sure to grind away the teeth and a little more after all traces of the teeth are gone. Stamping the teeth affects a little of the depth below the lowest of the grooves. You want to remove that. With it being annealed you can cut it with hacksaws or files easily enough. But grinders is an option.
After shaping it and bending it to a good starting shape you can heat it back up to a good cherry red where it can be tested with a magnet. If it's no longer magnetic then it's ready to dunk in warm water to harden it. Hot tap water with a spoonful of salt is a good option. Polish it up so you can see the colors that form in the next step. What you do now is over a very low propane flame heat it up until you start to see colors appear. Heat it very evenly. It'll pass through tan to brown and then purple and blue. When it's evenly all an electric blue dunk it to stop it getting more tempered. A good way to do this is lay the spring onto a piece of sheet steel that is at least 1/16 or 1.5mm thick and heat both. The tray will spread and more evenly heat the spring. And when it's up and turning purple lift the tray out of the flame and let the colors catch up. Likely as not you'll see it even up and shift to the electric blue even out of the flame. Slip it into the water at that point to stop the temperature rise.
I know this all sounds pretty fancy. But consider that it's a skill you can learn. And you can try the hardening and tempering on a scrap of the tool steel before you commit to the carefully made replacement. Cost wise a suitable swirl style propane torch is up around $50 and it'll cost you another $20 to $25 for the materials to make up and put some feet on the soup can forge.
Your idea of re-tempering is a non starter. It won't alter the shape. And if you over temper it then it's part way to being annealed and will actually more easily take up a new collapsed shape. Do not do that.
So first up you'll need a heat source to work with some tool steel to make a spring. You'll use this for both annealing any hard materials to work them and later to heat up the metal again to harden it. An option that is very low in cost and works super well, using it myself in fact, is a "soup can forge" using a swirl style propane torch for the heat source. Do a search on You Tube for "soup can forge". Hint, instead of all sand to go with the plaster of paris I went with 1/3 sand and 2/3 perlite. Better insulation properties. Does it help? Not sure but my simple forge works very nicely and heats up fast.
Next is to get some tool steel that can be hardened and tempered. Old dull files are one source. But of course there are a lot of other options too. If you use a file be sure to grind away the teeth and a little more after all traces of the teeth are gone. Stamping the teeth affects a little of the depth below the lowest of the grooves. You want to remove that. With it being annealed you can cut it with hacksaws or files easily enough. But grinders is an option.
After shaping it and bending it to a good starting shape you can heat it back up to a good cherry red where it can be tested with a magnet. If it's no longer magnetic then it's ready to dunk in warm water to harden it. Hot tap water with a spoonful of salt is a good option. Polish it up so you can see the colors that form in the next step. What you do now is over a very low propane flame heat it up until you start to see colors appear. Heat it very evenly. It'll pass through tan to brown and then purple and blue. When it's evenly all an electric blue dunk it to stop it getting more tempered. A good way to do this is lay the spring onto a piece of sheet steel that is at least 1/16 or 1.5mm thick and heat both. The tray will spread and more evenly heat the spring. And when it's up and turning purple lift the tray out of the flame and let the colors catch up. Likely as not you'll see it even up and shift to the electric blue even out of the flame. Slip it into the water at that point to stop the temperature rise.
I know this all sounds pretty fancy. But consider that it's a skill you can learn. And you can try the hardening and tempering on a scrap of the tool steel before you commit to the carefully made replacement. Cost wise a suitable swirl style propane torch is up around $50 and it'll cost you another $20 to $25 for the materials to make up and put some feet on the soup can forge.
you should check the lower butt strap for a small screw that puts tension on the mainspring. Don't know if your S&W has one but many revolvers haves the bottom end of the mainspring in a notch in the metal framing of the butt and a screw part way towards the trigger guard that adds tension as you screw it in
cheers mooncoon
cheers mooncoon
Done that! The screw was backed out when I got it and turning it back in didn't alter the heavy pull at all. To BCrider, thank you but I live in an apartment and don't have the skills or space to attempt something like you suggest. Also, it's not just a straight spring. It has arms on the end where it meets the action and those arms engage an actuator. I'll give it some more thought. Odds of finding a replacement spring from some baffed out donor pistol are very unlikely but one can always hope.
The acoustics of his workshop are atrocious, I could barely understand what he as saying. Afraid that I was not impressed by what I saw. I thought he was letting the metal get too cold while he was bending and especially hammering. I also question cold bending what appear to be trigger springs on the shotgun frame.
cheers mooncoon
Post a pic. If the spring is similar to a more modern N frame you can likely use one of those. - dan
