"straight mainspring"????

[Michael]

I was doing the final fitting for a forged mainspring on a musket lock I am making. This idea came to me: Why does the spring have to bent around 180 degrees creating a 'knuckle' that is a potential weak spot where the spring could fail? Would a straight mainspring work just as well? What I envisioned was a spring that was just the bottom leaf of a conventional main spring with the hook on the working end to provide clearance for the tumbler as it was cocked. This is a big musket lock, 7 3/4" long and there is about 4 1/4" between the toe of the tumbler and the forward lock nail. This spring would taper in both width and thickness to provide the flex and strength need for a good mainspring. It could be fastened to the lockplate  through a boss at the end of the spring near the front locknail and a peg through the plate in the usual manner. The spring would do all its flexing beginning where the peg ends and bend from there like a two leaf mainspring.

A spring made like this would certainally be easier to make and and less likely to break. Another benefit would be less wood to remove from the lock mortise helping to strengthen that area of the stock.

Any reason a spring like this would't work???

Michael

[Acer Saccharum]

The pin and peg would have to be sturdy. There will be tremendous effort by the flat spring to twist and fly out if the peg can't hold the spring straight and square.

[Long John]

The shape of the mainspring is quite intentional; it comes from Hooke's Law.  The curve on the spring is intended to lengthen the working (bending) part of the spring.  According to Hooke's Law the deflection force is proportional to the CHANGE in position of the spring divided by the length of the working section.  By making the working section of the spring longer (with the bend) the spring is lesslikely to break and provide a more uniform force. 

Forged springs start out straight, taper gradually and are bent to get the long spring into the relatively small place.  The cast springs lack the gradual taper of a forged spring and consequently have shorter working sections.  The shorter working sections make them more prone to breakage.  Fortunately, our moder locks are made from superior steel alloys that permit relatively large deflections over relatively short sections without breaking. 

Also, a straight spring as you have described would place a very large force on your little pin and might even shear it off.

Best Regards,

JMC

[Acer Saccharum]

by hooke and by crooke.... we have come to spring.

[Roger Fisher]

by hooke and by crooke.... we have come to spring.

Hookes and crookes in Washington (D.C) mostly

[The other DWS]

the Flintlock is, like a mechanical watch movement, the product of a long and convoluted evolution over half a millennium.  Back when the flintlock (igniting muskets, rifles, cavalry carbines, pistols, and artillery) was the epitome of military might; kings and kingdoms invested a lot of brainpower and money in development and improvement.  In its percussion lock form it probably reached the peak of development in the incredibly fine sporting and target rifles of the 1870's and 1880's.   Even at that point they continued to rely on the "folded" mainspring.

While we may be able to make some improvements to the lockwork due to modern metallurgy and heat treating, low friction surface treatments, a higher degree of precision in machining and fitting the use of the folded main spring have pretty well proved unimprovable.  

I have a back action lock on my Earle-Wesson express rifle.  absolutely state of the art mfg and metallurgy.  I talked to Steve about this at great length since he machines and heat treats the folded mainspring out of some exotic space age steel alloy.  He said that given the space constraints and working dynamic requirements there is basically no way to improve on the folded spring design.

 I think the only way you can possibly improve on it is to adopt some sort of coil spring technology as was used in some back action locks for various hammer double guns.  I have a vague possible memory of some percussion repros---maybe spanish or Italian made that had coil springs.  If my recollection is correct my cousin had one, for a short while,  and it was "mushy" feeling and very unsatisfactory

[Acer Saccharum]

The Rem Roll block uses a straight spring, screwed to the frame by a hole.

Another thought, if you use the straight spring, make sure the lock plate can handle the torque.

Let us know what you end up doing.

Tom

[Dphariss]

I was doing the final fitting for a forged mainspring on a musket lock I am making. This idea came to me: Why does the spring have to bent around 180 degrees creating a 'knuckle' that is a potential weak spot where the spring could fail? Would a straight mainspring work just as well? What I envisioned was a spring that was just the bottom leaf of a conventional main spring with the hook on the working end to provide clearance for the tumbler as it was cocked. This is a big musket lock, 7 3/4" long and there is about 4 1/4" between the toe of the tumbler and the forward lock nail. This spring would taper in both width and thickness to provide the flex and strength need for a good mainspring. It could be fastened to the lockplate  through a boss at the end of the spring near the front locknail and a peg through the plate in the usual manner. The spring would do all its flexing beginning where the peg ends and bend from there like a two leaf mainspring.

A spring made like this would certainally be easier to make and and less likely to break. Another benefit would be less wood to remove from the lock mortise helping to strengthen that area of the stock.

Any reason a spring like this would't work???

Michael

Its made that way because it works better.
The upper leg also flexes and stores energy as the cock is drawn back.
The straight leg spring will likely have a higher stress since it will be much shorter and be more difficult to anchor.
If they worked better the straight spring would have replaced the "V" hundreds of years ago.

Dan

[Pete G.]

by hooke and by crooke.... we have come to spring.

You're a bad man.........

[Acer Saccharum]

I was whipped many a time in Catholic school. I don't know why, really. They never made me cry, just mad. I have been trying to get even ever since. You guys now have to bear the brunt of my childhood anger. 

[Acer Saccharum]

Sorry, off topic.

I am curious about the straight spring idea. I wouldn't want to squash the idea right out of the box. But you know, as we all do at times, that something has come about because it worked, and then adapted and tweaked through many generations until it could evolve no more. Thus, the bent mainspring.

However, you have a case here where Michael has enough length, and given proper support, the straight spring could function. But I doubt anyone here has the experience in straight springs to say. So the proof falls on Michael's shoulders. If you do this, Michael, I'd like to know how it works. I don't doubt it could. But it is in the details that makes a success or failure, so do your homework.

Tom

[Dphariss]

I have not the slightest doubt it will work if properly done. But I wonder if it will provide as much force with equal reliability. Like you if he wants to do the work its an interesting experiment.
A good mainspring is notoriously reliable. I used to replace all my repro sharps springs with original Spencer (same lock internals as Sharps) springs which likely date to the Civil War. They still worked great, better than the repro springs and never had one break.

Dan

[Jerry V Lape]

You might want to consider this a little differently.  The opportunity to have the long straight spring also means you have the room for the advantages of a extray long bent spring - a technology long proven.  The straight spring could most likely be made to work, but it probably couldn't be made to work as well as an extra long bent one.   So perhaps the effort would be better spent making the long bent spring. 

[Michael]

Thanks everyone for your input.

This idea came to me as I was filing up the peg on the mainspring on my current build. What I pictured this spring to look like would begin with a flat 'tab' or boss at the end through which a screw could be used to fasten the spring to the plate much like a military lock. A short distance from the screw would be the peg. Exactally what the shape and size of this peg would be, would have to be determined by trial and error( I'm pretty good at this part!!).

I realize the this peg will be under a lot of strain because this is where all the work of the spring begins.  Maybe more of a longer tab shape rather than a round peg as used on a folded mainspring. From this point the spring would taper in both thickness and width just like the long limb of a typical mainspring. The spring would end with the normal hook at the end to allow clearance for the toe of the tumbler as it rotates when pulling the cock back to full cock.

The spring would still have the 'preload' required of a folded spring to make it work along its entire length. Its final thickness and width would be determined by filing and trying and filing and trying,etc. I'm would be inclined to make this spring out of my stash of 1075 spring stock to keep the heat treating simple.

I don't know if the size of the lock would be a limitation for such a spring. If it works I can see that it would be more difficult to get to function right on a small lock such as a pistol or small rifle lock.

At any rate just an idea.....


Michael

[Dphariss]

If you search the WWW for the Lewis and Clark Air Rifle you may find a photo of a lock with a straight spring.
But the original did fail in service.
You will also note that it does not function as one would expect in this rifle.
http://www.beemans.net/Austrian%20airguns.htm
Dan