Spring Weld - "V" Type Mainsprings

[rhmc24]

This is about the 'V' shaped springs commonly used on guns from the flintlock, percussion & early cartridge types using a side-lock. Little application on modern guns but may be of general interest to gun-folk.

I had a mainspring broken at the elbow in an antique repro derringer. Beautifully made piece, one of a cased pair. I did my usual weld repair, carefully re-fitted the spring and re-tempered it. It broke first try - maybe my second or third spring failure in 30 years.

I decided the spring must have been made of some modern alloy steel rather than basic carbon steel, which responded differently to my temper method. So I made a carbon steel (SAE 1095) duplicate of the broken piece, welded it in place, tempered it and it worked as planned. A learning experience. This particular spring was about quarter inch wide and .050" thick at the weld point. See sketch ---

The flex part of the spring can not be welded and retempered due to the heat of the weld destroying the carbon content. So I weld at the part where it is static, that part of the spring that positions and holds the flexing portion.

For this kind of fix, I taper the attach area so that there is a "fulcrum" about quarter inch away from the actual weld which is at the elbow. With the fulcrum point distanced from the actual weld, normal tempering works. This in effect shortens the spring somewhat which would give it more spring force and possibly over-tax its strength. I carefully thin the spring either in thickness or width (or both) to relieve its tension.

As described above, I have usually made the new piece I weld on. That is much easier and quicker than making an entire spring. For some I have cut the desired piece off another old spring.

I use a MIG welder which produces a local heat. In the past I used stick arc welder doing the same kind of repair on big mainsprings for military pieces. Gas welding is slow and would produce too much general heat, requiring re-tempering the spring.



It is worth repeating that 'restoration' of pre-cartridge, primarily guns of 'lock, stock & barrel' type, has a different meaning than modern restoration to like new a la Turnbulls. Early gun collectors want the gun as it was in its use-period, showing its evidence of normal use & abuse, which usually means restoring to original configuration of barrel length, perc back to flint, etc. --- all appearing as near as possible to be original, no evidence of restoration ------>

[Ivan the Butcher]

It is nice to know about these things! Not that I'll ever use that knowledge. But thanks for sharing.

I know that side lock mainsprings are a pain to install, and the Civil War and Trapdoor Springfields needed a small vise to contract the spring enough to slide it into position. I forget how good/easy we have it today and sometimes complain about "captured" coil springs.

Ivan

[Jim Mayberry]

I had a gunsmith friend in Denver, Colo. that searched for sheets of asbestos around old boilers in buildings that were being torn down. He would make a v spring, heat it to the right temp. wrap asbestos around the spring and let the v spring cool. He said the longer it would take to cool, the better the spring would be. He told me it would either break right away or last for years. He repaired many an old double shotgun that springs were no longer made for. Sorry I could not remember his name.

[DWalt]

I once had a Civil War-era caplock musket, Belgian, I think, I never could positively determine its origin. It also had a V-spring, broken at the bend. I simply brazed it together with no further heat treatment or tempering. It seemed to work OK in popping musket caps, but the hammer blow seemed a little light to me. I used to shoot glass marbles in it, and I could actually shoot a fairly tight group at 100' or so, even without any rear sight (it did have a small front sight).

[Ivan the Butcher]

Originally Posted by Jim Mayberry

I had a gunsmith friend in Denver, Colo. that searched for sheets of asbestos around old boilers in buildings that were being torn down. He would make a v spring, heat it to the right temp. wrap asbestos around the spring and let the v spring cool. He said the longer it would take to cool, the better the spring would be. He told me it would either break right away or last for years. He repaired many an old double shotgun that springs were no longer made for. Sorry I could not remember his name.

In High School, I had metallurgy classes. They taught us to "slow cool" heat treated items by shoving them into (very dry) mason's sand or "Green" casting sand. Wrapping them in anything, would be too slow and cumbersome! (not to mention the health risks!)

Ivan

[steelslaver]

Nice repair job. Solid thinking leads to good results.

Don't mess with asbestos. Go to a refactory supply and ask for KAOWOOL
It is a ceramic fiber material and has very good insulating properties and will take the heat necessary to slow cool tempering temps. You can also encase the kaowool in a fiberglass fire blanket envelope. This will keep the kaowool protected and keep its little fibers enclosed. No of it is good for you, even regular fiberglass insulation. Kaowool is itchy too.

[rhmc24]

I've been hearing the slow-cool recco for 50 years. Not to dispute but in my hundreds of springs made, I never practiced it. Maybe my springs won't last forever but so far, so good ------->

[DWalt]

"I've been hearing the slow-cool recco for 50 years. Not to dispute but in my hundreds of springs made, I never practiced it. Maybe my springs won't last forever but so far, so good ------->"

It's not necessary to slowly cool springs in asbestos or anything else after reaching tempering temperature. Air cooling works just fine.

[Drm50]

I don't wrap mine, but I do lay it on a piece of asbestos to slow
cool. Didn't want to lay on metal to draw heat out or wood which
would burn. The smaller the spring, the more trouble I have with
them. I have about a 50% success record, the other ones just
last 1 or 2 flexes. Got to point I would make 2or 3 while at it.

[DWalt]

The key is to get a thermocouple. They attach to your digital multimeter, not very expensive, and you get a direct readout of temperature. My procedure is to temper the spring in a small sand bath heated by a propane torch. I have used a tuna fish or cat food can for smaller springs. I normally temper springs at around 600 deg. F., no special method used to slow cooling. Some use molten lead for tempering, and that should work OK.

There are also those digital thermometers used for cooking, just point it at whatever you want to measure the temperature of, and they are fairly accurate. I have one of those, but have never used it for tempering. But I have used it for checking the temperature of M249 and M240B MG barrels after extended firing.