Mainspring design

[keweenaw]

Acer,

No those arms don't touch, they miss by a couple thousands, about like Bob's cigarette paper.  The spring maker who did those was a real master of his craft, not the slightest kink or unevenness in that spring as it loads.   The one on the other lock is exactly the same.  The problem with one arm hitting the other when it's loaded is that it puts entirely different stresses in the spring that go across the spring rather than along its length.  Think of a sheet  of glass.  It will bend quite a bit without breaking if you put the two ends on books and push down gently with your finger but if you put it down on a grain of sand on your  bench and apply any pressure it will shatter.  Now most flintlock springs have a lot more beef to them so that a slight touch just at full load probably won't break it but if it hits hard or much before full load the contact area is where it will eventually fail all other things being equal.

I've seen some truly terrible springs in new commercial locks by makers other than Chambers.  Gross over arches, etc.  That's because the masters for some cast springs aren't particularly carefully made.. Judicious filing of the overly stiff base of these springs so that they become a smooth, even taper will take out the overarch and actually speed up the lock as the load goes out of the spring evenly and not in a uneven, vibrating, manner.  Those old English shotgun locks by the Mantons and the best lock makers of their day are the fastest flintlocks ever made and by current cast spring  standards the springs look very thin, but those springs are perfectly made and that's what makes the difference.  The title of this thread "Mainspring design" says it all.

Tom

[Jim Kibler]

Again study good original work and use it as a guide!  Seems pretty simple.  Not sure why it's so often overlooked?

[timM]

I have attached a couple of photos of an original lock out of an early 19th century master built rifle.  Note the radius of the spring bends.  Whether or not the main spring is original,...it is old.  I hope the photos are enjoyed.

It would seem that the American gunsmiths and their customer needs were meet with a lock of  reasonable quality, not much more and sometimes less.  As always there are exceptions.....I would love to handle / inspect a John Armstrong lock!  tim

[smart dog]

Hi Bob,
I've made quite a number of springs and several that use the basic design shown in Tom's photos of the John Manton lock.  They all have noticeable radii and gaps, although very small.  I have yet to make a spring like the one Tom shows in the Westley Richards lock.  That is a beautiful spring and looks similar to the springs in my own English made late persussion side by side shotgun.  Of course, they function wonderfully.  How do you close the radius and gap completely like that?  Do you heat the spring and hammer the leaves together?  I do not have a forge and use a welding torch for heat.  I usually start the bend by bending the leaves using pliers while heating.  I then finish the bend by heating and pinching the spring in a vise.  I do it that way because I only have 2 hands and I can hold the heat on the spring while simultaneously closing the bend but cannot seem to close it completely.  Perhaps if I make a stand for the torch handle and then hold the spring in pliers, heat and bring it down on my anvil for hammering, I could close the bend.  Would you be willing to give me some guidance on this?

dave   

[Bob Roller]

I do hammer the spring limbs together but use what Bill Large called a "flatter",
a piece of 5/16x1 steel in this case. I also clamp the unbent spring in a vise vertically
against another piece of 1/8x1 steel. The spring is marked as to where the bend should be
and I use a Presto-lite "B"torch like plumbers use as a heat source. It is a mixture of acetone
and acetylene that produces a hot blue flame and to me is ideal for this job. I heat the spring
at the bend point with a #5 tip and when it is hot enough,I then hit it with a hammer to bend it around
the 1/8x1 steel plate.After that start,I remove the partly bent spring and clamp the torch in the vise and
reheat the bend while holding the spring with a pair of duck bill pliers and then when hot enough,the
"flatter" is used to flatten the upper limb to the lower limb with special attention being paid to the bend.
The spring is then allowed to coola and then a taper is milled into the upper limb on a milling machine.
I also use the milling machine to establish the taper in the lower limb by clamping the blank to a fixture
that has the taper already predetermined.This procedure eliminates a lot of physically tiring filing and
produces a good looking spring as well as a good functioning one.
Send me your personal Email to <bobroller@frontier.com>and I'll see if I can send you a picture of
the Stanton lock copy I make.

Bob Roller