Lightening a Mainspring

[Versanaut]

I built a little Left hand 32 kit for my son a couple years back and it loves to eat mainsprings for breakfast. The lock is a larger CVA percussion cap lock.

The original spring was well balanced and lasted about a year. (Shooting monthly matches, one squirrel hunt, some range time teaching my son to use it). The next 3 went in quick succession. One broke installing, two broke while firing in the mortise damaging the wood. These all were VERY tight and the hammer was quite stiff to Draw back. Got one in there now, but haven’t been shooting it as the hammer draw is so stiff. All replacements were CVA parts from Deer Creek.

My son has moved on to a flinter. Now my daughter is interested, a lefty too so I want to get that little rifle back in action.

I need help getting the mainspring to behave. I ordered both sizes of springs from Deer Creek. One clearly has a smaller ‘gap’ To compress but even it is really compressed going in and is a tough draw.
Just for clarification, I am using the mainspring tool from ToW to install these. Eye protection, and gloves

I thought about filing off some material. Don’t like that idea. Teeth marks tend to stress fracture. Wrong area will weaken the spring or cause it to want to pop out of the lock

Thought about changing the ‘Set’ with map gas in a vice. Not sure the proper heat treatment for the spring if I did this. Afraid I might make it too brittle or too soft.

So, here I am before our guild of builders looking to learn a thing or two. Thanks in advance!

 

[Pete G]

File the spring thinner, particularly any sharp edges using strokes along the length of the spring then polish well.

 

[Grenadier1758]

@Pete G is correct. File along the length of the spring and you won't create the teeth marks. Be very cautious at the bend.

@Versanaut, where were the springs breaking?

 

[Gun Tramp]

File the spring thinner

Hmmm...pretty risky business. Filing the spring narrower is usually suggested; I've used this method with success.

 

[rich pierce]

Reducing width by 25% reduces spring strength by 25%. Thinning by narrowing reduces strength proportionally.

Thinning reduces strength relative to the square of the thickness


3/4 times 3/4 = 9/16. 4/4 times 4/4 =16/16 or one (unchanged). 16/16 minus 9/16 = 7/16 loss or 43% loss.

 

[Larry (Omaha)]

If a spring is too stiff it for sure compresses harder, but that should not make it break. When you install the next spring make sure it is not too long or binding anywhere. Just because it if for your gun does not mean it is perfect fit. You may need to trim it a tad. If your compression is too stiff, grind lengthwise to thin. I usually grind the flat, but grinding it narrower works too. All grind marks need to polished out. If a spring fractures while using and is not in a bind most likely the hardening process was not tempered enough. (We are talking hundreds of compressions, but they can fail eventually) If the spring was tempered too much, the spring will not spring back to original shape when compressed. Oil at the spring/tumbler contact is must. Hope this helps.
Flintlocklar

 

[SDSmlf]

There seems to be some interchanging of terms spring thickness and width and potential confusion, at least in my opinion. On flat V type springs I would always narrow or thin the width, with the width being 90° to the V, or the direction of the red arrows in the photograph.

 

[Zonie]

I agree with the idea of reducing the width of the spring if a person wants to reduce the springs strength. It is the safer way to do it.

Reducing the thickness, like Rich mentioned, changes the springs strength VERY rapidly. If a person doesn't understand what the square of the thickness means, it means the springs force will change a LOT even if only a little bit of material is removed. When that happens, the stresses in the spring in the area where the material was removed increase just as rapidly and that can lead to a broken spring.

All filing or sanding MUST be done in the direction of the length of the material. Minor roughness in this direction won't cause a problem.

If we are speaking of roughness across the width or on the edges of the leaf, it is a much different matter.
Even minor roughness across the width of the spring will cause dozens of scratches that will rapidly grow into cracks when the spring is bent. Once a few cracks are made, one or more of them will spread across the width of the spring resulting in it breaking.

 

[Versanaut]

I appreciate all the great feedback. I am surprised to learn so many folks work the spring size to tune them for lack of better term. Good to know. I'll post some pics in the morning. I have some questions about where is best to thin and all, taking into account what was mentioned above. All of these springs have a lip on the flat. I presume to catch a lockplate groove to prevent the spring from slipping from out. Also , all the springs have a 'crease' in the bend where a little of the metal pushes out presumably when they folded it over. Pictures will show it better. I have to think that is a stress riser to Grenadier's point

@Grenadier1758 All the springs broke in the bend.

Pictures to come tomrrow.

~Versanaut

 

[SDSmlf]

If you have another spring from the same supplier I would probably sit it in an oven set between 400°F and 500°F for about an hour to temper it. Guessing on temperature not knowing exact spring material.

 

[Versanaut]

.... I would probably sit it in an oven set between 400°F and 500°F for about an hour to temper it...

This is where I originally was headed, but I’m not sure what works best for springs.

 

[Versanaut]

Ok. Pictures... If they will post from my phone here.

Broken spring

Note the ‘fold’ material bulge at top arrow. The tab on the flat. I assume if I remove material, should be on the side opposite the lock and don’t mess around the bend.

The area between the arrows actually closes and touches when compressed. This loads up that bend/fold a lot.

The two sizes from Deer creek. Same dimensions. Just a little more bend. Interesting note. Both came in same bag unlabeled. I’m not sure which is which.

The groove for that spot on the flat

Installed at half cock. Already compressed Nearly flat and touching.

Thanks again!

 

[jager43478]

I built a little Left hand 32 kit for my son a couple years back and it loves to eat mainsprings for breakfast. The lock is a larger CVA percussion cap lock.

The original spring was well balanced and lasted about a year. (Shooting monthly matches, one squirrel hunt, some range time teaching my son to use it). The next 3 went in quick succession. One broke installing, two broke while firing in the mortise damaging the wood. These all were VERY tight and the hammer was quite stiff to Draw back. Got one in there now, but haven’t been shooting it as the hammer draw is so stiff. All replacements were CVA parts from Deer Creek.

My son has moved on to a flinter. Now my daughter is interested, a lefty too so I want to get that little rifle back in action.

I need help getting the mainspring to behave. I ordered both sizes of springs from Deer Creek. One clearly has a smaller ‘gap’ To compress but even it is really compressed going in and is a tough draw.
Just for clarification, I am using the mainspring tool from ToW to install these. Eye protection, and gloves

I thought about filing off some material. Don’t like that idea. Teeth marks tend to stress fracture. Wrong area will weaken the spring or cause it to want to pop out of the lock

Thought about changing the ‘Set’ with map gas in a vice. Not sure the proper heat treatment for the spring if I did this. Afraid I might make it too brittle or too soft.

So, here I am before our guild of builders looking to learn a thing or two. Thanks in advance!

Who ever is making the springs it sounds like the heat tempering is not right the springs are too brittle. If you have a replacement spring heat temper it in your oven around 375 deg around 40 minutes and let it air cool . I thin all my frizzen and main springs on a belt sander using the roller part sanding lenght wise and then I polish them using different grits of sand paper. Most springs are made so the lock will spark and work this is why they need to be tuned to work and give you more flint life. I can get up to 100 firings or more with my flints this includes napping.

 

[mooman76]

I find this interesting. I have a sort of unique gun with this type of main spring. It had a real sweet trigger pull when I got it but that didn't last long as they ground off too much and the more I shot it, the more it wouldn't work because it was weakened too much. I would like to make a spring and I was wondering if there was some sort of booklet I could get that gives me information on forging springs, hardening and tempering? I also have sever other old guns that need new springs.

 

[jager43478]

I find this interesting. I have a sort of unique gun with this type of main spring. It had a real sweet trigger pull when I got it but that didn't last long as they ground off too much and the more I shot it, the more it wouldn't work because it was weakened too much. I would like to make a spring and I was wondering if there was some sort of booklet I could get that gives me information on forging springs, hardening and tempering? I also have sever other old guns that need new springs.

I have a book called Gunsmithing Simplified No1. SPRINGS By Kit Ravenshear Published by NORMANS of Framlingham Ltd. The tells u how to make springs, small paper back. TOTW may have something book wise. There's a website called hootalrifleshop.org. he shows u how to make springs.

 

[Flintandsteel]

First of all, there has to be a reason the spring are breaking. It’s a percussion lock and the Spring isn’t usually as Strong as a flinter.
Almost seems like there’s got to be something else to fix the issue.
Having a new, properly designed one might be the fix.
ive been building flinders fo over 30 years, and have only seen one broken mainspring in that time.
Gotta be something else wrong.

 

[GREENSWLDE]

The trouble with modern machine made springs is that they are made from a different steel to those made 150/200 years ago. Before you start to make your own go to a scrap(junk)yard and ask if they have any old carriage or cart(buggy)springs or early lorry springs. These have the grain structure along the length. Cut your leaf from along the length NOT across. and go from there. I am a spring maker with a history of spring makers. Modern materials are alloyed. Old springs were OLD Medium carbon steel that we called COMMON HARDENING STEEL which seems to be not made today. Go to the junk Yard first. Grain structure must be along the length of the spring..
OLD DOG..

 

[LRB]

This is where I originally was headed, but I’m not sure what works best for springs.

The correct temper heat for carbon steel leaf main springs is 725°F to 750°F. That heat gives about 42 to 46/48 Rc hardness. Of course that only applies to one that has been fully and correctly hardened.

 

[LRB]

The trouble with modern machine made springs is that they are made from a different steel to those made 150/200 years ago. Before you start to make your own go to a scrap(junk)yard and ask if they have any old carriage or cart(buggy)springs or early lorry springs. These have the grain structure along the length. Cut your leaf from along the length NOT across. and go from there. I am a spring maker with a history of spring makers. Modern materials are alloyed. Old springs were OLD Medium carbon steel that we called COMMON HARDENING STEEL which seems to be not made today. Go to the junk Yard first. Grain structure must be along the length of the spring..
OLD DOG..

Common spring steel is iron, carbon, and manganese. The same as most made sometime after the Bessemer process came in use for steel making in the early 1850's The 10XX steels are much the same as late 19th c. steels, except more pure. Not much different than the crucible steel of the late 18th c., except with a more controlled amount of carbon, and cleaner iron.

 

[LRB]

W

I have a book called Gunsmithing Simplified No1. SPRINGS By Kit Ravenshear Published by NORMANS of Framlingham Ltd. The tells u how to make springs, small paper back. TOTW may have something book wise. There's a website called hootalrifleshop.org. he shows u how to make springs.

Worst piece of trash Kit ever published.