Main Spring / Tumbler Toe Contact — Follow-up and a question

[silky]

Evening,

Attached are two pics of a lock I’m working on, with the new forged, hardened, and tempered mainspring. Three questions:

1. Is the main spring hook sitting too close to the end of the toe?

2. If yes, can I adjust the end of the mainspring without affecting the hardening-tempering, or does it need to be annealed, adjusted, then heat-treated again? I think I can reshape by filing the tip of the mainspring to sit a little further back, too.

3. If I adjust it, should I start by making the end of the hook not so long (the part that points downward)? I know that if I do, I’ll need to “pull” the end of the hook aft in order to maintain contact on the toe. As it is now, it looks a little non-standard.

This spring is ridiculously strong right now, but I want to address this geometry first, before starting to weaken it by filing the sides.

Thank you much!

- Tom

[smart dog]

Hi Tom,
There is a lot to unpack here.  The material for the spring is much too thick.  You really need to taper and thin the lower leaf a lot and should do that before you heat treat the spring.  I really do not like springs that butt against the bolster as yours does.  I much prefer a tab or lug on the end that lowers the position of the top leaf of the spring so you can fit it to a large diameter barrel without the spring interfering. The position of your hook is fine but I prefer it to be a lot thinner making sure there is room inside the bow for the toe of the tumbler at full cock.  I like the hook to slide almost all the way back on the foot of the tumbler at half cock.  Then when the lock is pulled to full cock, the tip of the hook is nested inside the instep of the tumbler and the tumbler actually rotates around the tip rather than lifting it up very much.  This gives you some mechanical advantage as well as making it easier to pull the lock to full cock. Those are all adjustments you can make before hardening the spring.  Here is an example of a big French musket lock that I worked over.  I forged the mainspring.  Note the hook position at rest and then full cock.  In my opinion, that is the optimum positioning.
 




dave

[rich pierce]

Great advice, Dave. In the at-rest position is there any advantage to having the tip of the hook closer to the toe of the tumbler?

Tom, that spring is beastly!  I usually take measurements of a spring that works well in a similar sized lock and go a wee bit thicker. Then if I need to remove some from the working arm, no problem. As I don’t do this often I have to take advantage of the experience of others - meaning locks in hand that work well. The shape of the lower arm arc when out of the lock is something I try to emulate as well.

[silky]

Dave & Rich,

What can I say? There are no wimpy springs in this shop!

My first attempt was too thin and weak, so it sounds like I over-corrected and there is plenty to work with here. I’ll anneal it and go to work on your recommendations.

The positioning of the original spring in all three positions is just as you explained, Dave, so I’m hoping I can emulate that with the new one. I did ensure the spring clears the barrel it’s going to be mated with, so good there; but in the future I’ll make them with the tab to gain working space.

The picture here shows, left to right, a Chambers Early Ketland I used as a guide, mine, and the original. The Ketland is a bit longer so maybe not the best template, but it did give an idea of where the tapers are.

Once annealed, should the soft spring be able to flex and bend without breaking while I check all three positions? It’s made of 1075.

Once the oven dings I’ll get at it and post an update and maybe some more questions. Thanks so much for your help, guys!

- Tom


 

[HighUintas]

Keep in mind this is a different lock.

I noticed the same thing on my Chambers late ketland. The mainspring hook engagement on the tumbler toe is minimal. I emailed them pictures and Jim responded that it is completely normal and there is nothing to fix or be worried about.

I will however keep an eye on it and the amount of deformation I get on the top of the lock plate where the flint cock shelf hits it. There's a bit now and over the course of it's life, I don't think it's unreasonable to think that it may deform enough to eventually become an issue.

[Bob Roller]

It has been decades since I used this style of mainspring and the one on the left is the style I made.After forming the lower limb I filed a radiused taper with a wide knife shaped file with no cutting edges on the top edge.Then I draw filed and polished it and after marking the area to be bent,it was heated orange hot and forged and then the upper limb is tapered and the stud that goes thru the lock plate is formed by careful filing or a hollow mill.After this the upper limb is tapered and polished.These springs can be made from .093/3/32 thick spring steel and my choice is 1075.It works easily and adapts to spring making for those with little experience in making any style of springs.
Bob Roller

[Ky-Flinter]

I will however keep an eye on it and the amount of deformation I get on the top of the lock plate where the flint cock shelf hits it. There's a bit now and over the course of it's life, I don't think it's unreasonable to think that it may deform enough to eventually become an issue.

I have a lock with similar engagement, and have also been concerned about the lock plate deformation situation.  So, here's a question for the experts.  Will hardening the lock plate stop/prevent the deformation?  Or will that just transfer the deformation to the cock shelf?  If the cock is hardened too, will that cause the cock or lock plate to crack because they're both hard?  Or, do I just worry to much? :-)

Ron

[Jim Kibler]

Yes, there is advantage to having the mainspring tip closer to the tumbler tip at rest.  This provides more power to be translated to the cock throughout the cycle.

[Bob Roller]

I have never seen lock plate deformation from the strike of the cock and hardening the lock plate is not really needed.I used to have to straighten lock plates from the foundry because someone used an air hose to eject the waxes from the mould.My own flintlock rifle made by Leonard Meadows in 1965 used a lock I made from the external parts of the Chet Shoults small Ketland wore out a Bill Large 45 caliber barrel twice.No indication of deformation of the cock or the plate.I have straightened many lock plates due to lack of quality control at the foundry that cast them and complaints did no good.Get it done,out the door and quality control not needed or considered.
Bob Roller

[rich pierce]

To your question about an annealed spring being able to survive testing: I’m betting it would take a set. But I have no data.

[Scota4570]

2. If yes, can I adjust the end of the mainspring without affecting the hardening-tempering, or does it need to be annealed, adjusted, then heat-treated again? I think I can reshape by filing the tip of the mainspring to sit a little further back, too.

The contact point looks decent to me.  One thing found was that having a large are of contact between the spring tip and the tumbler makes it run smoother.  I have used abrasives to increase the contact area by lapping the parts together. 

I have thinned mainsprings on the end of my bench top belt sander.  Go slow, keep it cool by dunking in water frequently. 

[silky]

Alright…

I found a better comparable lock in a Chambers Dale Johnson and used that as a guide in thinning down Ragnar the Mainspring. After annealing it, I used my bench grinder and files (I need that bench top belt sander) to bring it down. I ended up bending the tip of the spring ~1/32” back toward the tumbler, and all three positions look good. In its annealed state, the spring moved through the whole range of motion without busting.

After polishing and heat treating, the spring tops out at ~9.5 pounds of force moving from rest to full cock (haven’t fine polished the tip-tumbler contact point yet).The frizzen opens at 3.7, so a little less than the 3:1 ratio I’m shooting for. With the goal being a reliable sparker, is it worth tinkering to make the main spring stronger, or the frizzen weaker, or just roll with it? The last picture is the preload bend I put on the spring.

As always, you guys have the answers and I really appreciate you taking the time to help me learn this stuff… thanks!

- Tom

[rich pierce]

You made a mainspring that works! That’s an accomplishment. For those who do it often, no biggie, but it’s not simple at all the make one that lays and stays flat on the plate, rides the tumbler smoothly through all positions, has plate clearance at rest, and appropriate strength.

[HighUintas]

Very nice job! I wish my mainspring stayed flat on the plate. Not sure if it hurts anything, but the way it contorts itself at full cock bothers me because it is ugly haha

[silky]

Yup, it’s interesting to see how even a simple component like the spring can present so many challenges that have second and third order effects on other parts/functions. Just more respect and admiration for what those gunsmiths were doing 300 years ago.

Thanks for the help and encouragement, guys.

- Tom

[Bob Roller]

Evening,

Attached are two pics of a lock I’m working on, with the new forged, hardened, and tempered mainspring. Three questions:

1. Is the main spring hook sitting too close to the end of the toe?

2. If yes, can I adjust the end of the mainspring without affecting the hardening-tempering, or does it need to be annealed, adjusted, then heat-treated again? I think I can reshape by filing the tip of the mainspring to sit a little further back, too.

3. If I adjust it, should I start by making the end of the hook not so long (the part that points downward)? I know that if I do, I’ll need to “pull” the end of the hook aft in order to maintain contact on the toe. As it is now, it looks a little non-standard.

This spring is ridiculously strong right now, but I want to address this geometry first, before starting to weaken it by filing the sides.

Thank you much!

- Tom

[Bob Roller]

I tried to reply and it away but that spring looks like it has a sharp edge that is trying to recontour the tumbler.After I bought a milling machine in 1967 I started making the linked mechanisms for flintlocks and then I was using the external parts from the Shoults lock that had the old style mainspring.From what I have read and was told ny Lynton McKenzie years ago the locks seen on the high end guns from London and other places had springs made by skilled people who made only springs and the rest was done by filers whose skills speak for themselves.We have today the quality steels that were unheard of in the 19th century and as a lock maker I do appreciate the quality control the steels we have now.

Bob Roller