Mechanical Principles That Make a Lock Work Well

[Chris Treichel]

I keep seeing this come up in discussions...
There are a couple of topics on lock tuning or discussions of a specific lock but not in a specific way...http://americanlongrifles.org/forum/index.php?action=search2

When looking at a good lock what mechanical principles differentiate the good locks from the...well shoddy stuff. Yes, being historically correct to the time period means that early locks were very simple and later locks could be extremely complex... but, what are the principles that all good locks share to make a flint or percussion lock function properly. Even a simple lock without a bridle over the tumbler and parts pinned in place from say the 1690s can be well built and a 1830s one with links and rollers can be a pile of slop...

Some thoughts on what makes a good lock:

All surfaces mate well, everything fits
All wearing components heat treated and polished
Bearings for parts such as the tumbler and sear
Appropriate strength springs
Bridle is strong enough to resist forces enacted upon it by the rotation of the parts and springs.
Main Spring geometry
Tumbler geometry... use of link to mainspring appropriate
Use of rollers on mainspring, frizzen/frizzen spring etc

Lock geometry
   Rotating parts generate appropriate momentum and do not hinder each other or transit beyond the area of the lock (such as a mainspring with link that pop out of the bottom of the plate)

Flint
   Angle of the jaws hold the flint appropriately to strike the frizzen in a motion that shaves steel i.e. not    bashing the flint.
   Frizzen geometry holds the frizzen to keep the pan covered and directs sparks to the middle of the pan
   Frizzen bounce back

Percussion
   Head strikes the nipple square on

What other ideas do you have...

[hammer]

Some years ago I took square-on photos of all the locks by top English, French and German makers in a local small museum over here in England.  Famous collection since put in store.  Printed out and measured the angle that the flint struck the steel.  Then made arcs around flint edge travel and steel face travel and proved that the angle pretty much stayed the same throughout the rotation.  28 to 30 degrees, as close as I could measure it.  (  Except for one that was way off.   In blowing up the picture I discovered the cock was a replacement.  Matching engraving but not an exact match to the lock plate.)
That angle of 28-30 degrees is the critical factor.
Peter.

[Pete G.]

Tumbler axle perfectly aligned and fit to lock plate and bridle. This makes more difference than almost anything else on lock function and is a main contributor to problems with locks built from a kit. Not many have precision machine tools and not everyone has the expertice to operate precision tools properly. It takes a certain knack and I, for one do not have it. That's why I buy locks and Roller has more business than he wants to handle.

"A man has got to know his limitations."

[Acer Saccharum]

Fit and finish are everything for a durable and perfectly functioning lock. Decades of lock design and development went into these mechanisms.

What I assume to be a Germanic import lock, estimated 1770 to 1780:


The internals are super precise, and heavy duty, and beautifully finished.

[shortbarrel]

The best lock in the word won't work if the flint is not right. Someone screws a store bought flint into the cock and expects it to perform. I'm tired of hearing bevel up or bevel down, this don't work. The flint has to be chipped to fit the lock geometry.

[Dphariss]

That lock is a dandy Acer...

Dan

[Long Ears]

The best lock in the word won't work if the flint is not right. Someone screws a store bought flint into the cock and expects it to perform. I'm tired of hearing bevel up or bevel down, this don't work. The flint has to be chipped to fit the lock geometry.

That's a new one for me? Can you explain how you custom Knapp a flint to fit the lock? Bob

[Acer Saccharum]

I'm no expert on flint knapping, but there is a trick I use for best ignition. Well, several tricks.

1) place the flint in the lock. go into a darkened area, where you can see the sparks. Trip the lock. observe where most of the sparks go. Move the flint forward or back, bevel up or down, until you get the most consistent shower of sparks hitting the PAN. Not ahead of the pan or behind the fence. When you find the right bevel position and distance of flint from frizzen at half cock, RECORD this measurement, write it down and put it in the patchbox.

2) try different flints: French amber, black English, Missouri white chert, etc. Find the one that produces the best spark for your lock.

3) I should be doing my taxes. I'd rather be here.

[whitebear]

I'm no expert on flint knapping, but there is a trick I use for best ignition. Well, several tricks.

1) place the flint in the lock. go into a darkened area, where you can see the sparks. Trip the lock. observe where most of the sparks go. Move the flint forward or back, bevel up or down, until you get the most consistent shower of sparks hitting the PAN. Not ahead of the pan or behind the fence. When you find the right bevel position and distance of flint from frizzen at half cock, RECORD this measurement, write it down and put it in the patchbox.

2) try different flints: French amber, black English, Missouri white chert, etc. Find the one that produces the best spark for your lock.

3) I should be doing my taxes. I'd rather be here.

Don't worry Acer.  The I.R.S. will give you extra time because you are helping educate some ignoramuses.

[PPatch]

"3) I should be doing my taxes. I'd rather be here."

Not to worry... April 15th is overrated. Thanks Acer for your insight, sounds logical and knowledge a working man ought to know.

dp

[Sawatis]

Hey Acer
Looking at your lock...I can't even see hints of the screws in the plate...Is it just the angle I'm getting?  Usually even when polished smooth and patina'ed with time you can see the little circles.
They didn't make blind holes for the bolster screw, sear screw etc...did they?
John

[RAT]

I'm guessing the lock plate has blind screw holes so the screws don't go all the way through the plate.

One thing I didn't see mentioned is frizzen cam geometry and it's relation to the shape of the frizzen spring. I discivered this the hard way when trying to make my own lock from scratch.

[Mark Elliott]

Hey Tom,

If I send you the folders,  will you do my taxes?     I have local, state, and federal to do for myself and my mother and they are complicated.  I  hate them more and more each year.

[Acer Saccharum]

I think they call this a screwless lock, or something like that. A term for blind screws. It indicates a higher quality than the run-of-the-mill lock.

Here is the original gun. I find it odd that such a quality lock is found on a very plain, almost primitive, gun.

[Sawatis]

Thanks Tom...I thought I was imagining things!  Happens more and more it seems!
I have seen a few german locks...(trunk locks not rifle locks) ...that used blind-tapped holes, but this is the first time I ever notices it on  a flintlock.  I imagine some of the high end Jaegers probably had locks of this quality.
John

[Bob Roller]

Helmut Mohr  of Mayen/Hausen Germany shot an original Jaeger
in competition in 1980 at the World International Muzzle Loading
Competition held at the USMC base in Quantico. It was marked
Frederich Ries and dated 1671 and it had a thick lock plate with
blind holes for all screws.The sear arm broke on the last shot and
I took the lock home with me and repaired it with a new sear and
tumbler.The mainspring was going to come off the cam ramp so
I fely a new tumbler was needed.When Helmut and his wife got
to our home here in WV,he was surprised to see the lock fully operational
again.

Bob Roller

[Sawatis]

That sounds like a really challenging repair job, Bob!  Were you able to use the original sear screw? were the treads a finer pitch to give more contact in the shallow hole?  Do you by chance recall how thick the lock plate was? I made a few locks about 20 years ago...haven't since, but feeling the bug to do this again.
John

[Bob Roller]

No real challenge but it ate up a half a day in time. Yes,I did reuse the old screw
thru the sear but had to go modern on the cock screw.It had some old German
pitch I had no gauge for.Diameter I THINK was about .120 or American #5x40.
The plate thickness was at least 6MM or about 1/4" and it had no pan bridle.
I did another fix for Manfreid Kroschel on his Whitworth long range rifle.The tumbler
shank thru the lock plate broke so I made a new tumbler for it as well with fly and
all original dimensions as they used to be.

Bob Roller

[Sawatis]

Thanks for the info Bob. New tumbler, sear and cock screw in a half day...man are you fast!
John

[Bob Roller]

John,
Years of experience will add speed and accuracy.I knew Helmut and Mary
would be in our home the next day and having proper materials on hand
made the job go easier. The same for the Whitworth lock for Manfried.

Bob Roller

[Artificer]

Here is the original gun. I find it odd that such a quality lock is found on a very plain, almost primitive, gun.

Sounds like the original owner and or gunsmith knew what was really important, I.E. Good Barrel, Excellent Lock, stock fit correctly to the owner?  Everything else is icing on the cake?
Gus

[Artificer]

Helmut Mohr  of Mayen/Hausen Germany shot an original Jaeger
in competition in 1980 at the World International Muzzle Loading
Competition held at the USMC base in Quantico. It was marked
Frederich Ries and dated 1671 and it had a thick lock plate with
blind holes for all screws.The sear arm broke on the last shot and
I took the lock home with me and repaired it with a new sear and
tumbler.The mainspring was going to come off the cam ramp so
I fely a new tumbler was needed.When Helmut and his wife got
to our home here in WV,he was surprised to see the lock fully operational
again.

Bob Roller

Helmut was fortunate you were there, Bob.

That was an especially interesting shoot in that Hershel House brought a Team in traditional Rifleman's Dress and fired modern replica Kentucky Rifles in an Exhibition Shoot.  International Rules did not allow for reproductions at that time and after Hershel and his Lad's shot a score that would have won had they been allowed to compete, the International Committee changed the rules and added matches for reproduction guns. 

Gus

[hammer]

Re flint position in the jaws.    If the lock is properly built then the flint protrusion should be adjusted so the edge travels right to the bottom, nearly, before the steel springs away.  Ease the cock forward while easing the steel back, allowing the flint edge to slide down the face.   If the steel springs back before the edge has reached the bottom, or pretty much, set the flint back a little and repeat.  Or vice versa.

I have never understood this bevel up/bevel down argument.  Seems to me that locks are precise pieces of engineering that rely on everything being exactly, or near, repeatable to be efficient.  With flints coming in different thicknesses the only form in which the flint edge can be consistently presented to the same position, or nearly, and at the same angle throughout it's arc of travel is with the edge as an extension of the bottom jaw platform.   The only fixed parameter.   Bevel up just produces too many wide variables.

Peter.

[Acer Saccharum]

Re flint position in the jaws.    If the lock is properly built then the flint protrusion should be adjusted so the edge travels right to the bottom, nearly, before the steel springs away.  Ease the cock forward while easing the steel back, allowing the flint edge to slide down the face.   If the steel springs back before the edge has reached the bottom, or pretty much, set the flint back a little and repeat.  Or vice versa.

I have never understood this bevel up/bevel down argument.  Seems to me that locks are precise pieces of engineering that rely on everything being exactly, or near, repeatable to be efficient.  With flints coming in different thicknesses the only form in which the flint edge can be consistently presented to the same position, or nearly, and at the same angle throughout it's arc of travel is with the edge as an extension of the bottom jaw platform.   The only fixed parameter.   Bevel up just produces too many wide variables.

Peter.

Peter, while your argument seems sound, if the sparks don't hit the center of the pan, all the theory is for naught.  When and where the frizzen flips is a very important part of the engineering and tuning. Fast reliable ignition is the first priority in a lock. Whether your lock has bevel up or down flint should be based on best performance, not on principle.

Tom

[Chris Treichel]

So we should be able to take a compass with one pin on the axis of the tumbler and the other point should transcribe neatly into then just behind face of the frizzen so as to push it open as the flint shaves the metal...