Mainspring in the barrel channel***UPDATE***

[Cory Joe Stewart]

Hello all,

I know it is common for the mainspring to come into the barrel channel and be filed off the fit.  But I am wondering how much is too much.  I am working with a late ketland lock from Chambers on a mountain rifle project.  As you can see from the images the lock is not 100% inlet and already the spring is well into the channel.  How much can be safely filed off the mainspring and it still function correctly and safely?




As is always the case any advise from you folks will be greatly appreciated.

Coryjoe

[Jim Kibler]

Cut some off of the mainspring and then cut some out of the side of the barrel with a rounded chisel or rotary burr / mounted stone.

[Dave B]

What Jim Says.  You don't have far to go and the corner will just be bobbed off and a small bevel on the spring where its not going to matter at all on both points. Use Prussian blue on the spring and keep going on the inlet as your blue starts indicating on the barrel  file off  the blue on the barrel and re mark. Now file a little on the lock spring only at the point of barrel contact.  I would go at it back and forth till seated. The reality is you can get more bang for your buck by getting after the barrel. There  is at least a good 1/8" at that corner that is dead space. Cory was this a pre-carve with the lock pre-inlet? I only ask in that you can avoid this if you put the lock on the barrel and mark its best position with the fence in place at the point of the touch hole. When inlettign the lock now you know you have to stay below the mark you have indexed on the barrel. With a pre-carve and lock inlet you are stuck with making these modifications to get things lined up.

[Cory Joe Stewart]

The barrel was inlet, not the lock.  The lock is my fault, I cocked the very front a little high to avoid the ramrob channel since that was the problem with my first build. 

Thanks for the help fellas.  I will work on it some tomorrow once I am done with the honey do list.

Coryjoe

[smart dog]

Hi Cory,
This problem is common and you will find that a lot of guns have mainsprings that break through to the barrel channel.  The real remedy for this is to have mainsprings with long tabs that fit under the lockplate bolster.  That lowers the upper leaf of the mainspring, allowing it to clear the barrel channel.  Notice how low the upper leaf is on the lock below.  That solves the problem but unfortunately our commercial lock makers don't make them that way.



dave

[PPatch]

Coryjoe;

I am glad you asked this question since I am dealing with the same problem at present. My main spring pushed its nose into the barrel inlet just yesterday as I was bringing in the lock a final little bit and that stumped me, now I have the answer.

Good luck on your build and thank you.

Dave

[Bob Roller]

I am not a "commercial"lock maker in the definition of production work but on locks that require
an upper limb with a turned up end to secure it under the lock bolster,I make them that way.
Most of these are in the Ketland.Chambers Ketland,3 different L&R types that I use as a basis
for my flintlocks.
The caplocks usually have a milled plate and I make them to use a "shotgun"style mainspring that
works quite well.I wouildn't think of making a mainspring like the one in that lock shown with such
a horse shoe bend and the claw to the stirrup needs attention as well.

Bob Roller

[Mark Elliott]

I grind the mainspring to fit up against the barrel and only cut the wood away where I must.  Usually,  I just cut away enough wood for the spring to just touch the barrel and only a slot in the wood about the thickness of the spring leg that is touching the barrel.   Generally,  I break through to the barrel channel at the upper end of the upper leg of the spring and at the bend of the spring.   I always grind on a bevel to match the flat of the barrel and maintain the geometry of the spring.   Also,  always grind, sand or file length wise along the spring, not across the spring.   It is best to polish this edge so as to eliminate scratches that can be the source of a stress concentration and fracture.    Taking a little off the top leg of the spring is not going to significantly affect the strength of a well made spring.  As in all cases, take away only as much metal or wood as is necessary.   

[Jim Kibler]

One thing I've noticed...  Many if not most original springs I've encountered, even on fine English or continental pieces, were finished much more coarsely than we seem to think is necessary today.  I'll admit to being in this camp.  File marks being stress risers is something that makes sense, but I suspect it doesn't have the impact we sometimes beleive it does.  It's not uncommon to see file marks at a fairly steep angle relative to the spring axis as well.  Just some things to consider.

[smart dog]

I wouildn't think of making a mainspring like the one in that lock shown with such
a horse shoe bend and the claw to the stirrup needs attention as well.

Bob Roller

Hi Bob,
Please explain your statement so that I can learn from it.  I made that spring.  The lock is copied from an original Wogdon pistol and I made all of the springs and screws. It is one of a pair and they function superbly, in fact they are the best pistol locks I've ever fired.  The open bend was designed such that when at full cock the lower leaf of the spring clears the upper leaf and makes a straight line to the stirrup (i.e., no bend in the middle of the lower leaf).  An alternative would be to pinch the bend tighter but have the upper leaf angle downward. The claws on the springs are beefy because the springs are very strong.

dave 

[Bob Roller]

Using that picture as a guide,it looked to me like the upper limb on that spring was too
high.As to the horse shoe bend,when I was learning to make V springs over 50 years ago
I was told that the sharp forged together limbs seemed to work better and rarely broke.
If you have an original antique English lock with such a spring as is shown'you have an
oddity. I have made it a point to look at every English and German lock I can and have
never seen such a spring. The bottom line is,if it works and gives no trouble,it is a good
one and only time will tell that. One reason so many European/English locks survive in
pristine condition is apparently they were little or seldomly used.

Bob Roller

[T*O*F]

Dave,
Perhaps pictures speak louder than words.  Here's one of Bob's locks; at rest and at full cock.

[Jim Kibler]

I've got to say, that that backwards bend at full cock is less than desirable.  For a well designed, set-up lock, the spring should ideally be straight at this position.

[FL-Flintlock]

I've got to say, that that backwards bend at full cock is less than desirable.  For a well designed, set-up lock, the spring should ideally be straight at this position.

And the reason would be?
Mark

[Jim Kibler]

Well, I wish I could give you a good reason but I can't   I'll just put it this way.  When you study finely made original locks, no matter where they were made, there was an obvious effort to set them up this way.  It's also commonly accepted as one characteristic of a well made lock today.  If someone is building a custom lock, it is certainly something the builder wants to obtain.  Perhaps Flintriflesmith might have some thoughts. 

Jim

[smart dog]

Hi Lads,
I started a new thread about mainspring design so that we don't distract from  Cory's original question.  Perhaps we could move the discussion about spring design there? Cory, I apologize for straying from your good question, one that affects many builders including myself.

dave

[Cory Joe Stewart]

Hello everyone.  I followed your advice and got the lock inlet and the barrel are both resting comfortably togther.  It did not require as much material removal as I imagined when I was laying in bed worrying about it.  Notice how much bigger gaps are when you are thinking about them after the fact.

Anyway, I really appreciate everyones help and you all taking the time to lend advice.





Coryjoe

[Acer Saccharum]

What's the problem? Looks good to me! 

good job. sometimes things like this can really be a mind-bender, until you see the makers 200 yrs ago ran into the same problem.

[whetrock]

Hey Cory,
Good job with the fix!

I wanted to add a few notes about touch hole position in relation to mainspring. This is not about your current build, but may be of use to you in the next one...

As Dave B mentioned above, this problem can often be avoided by checking how the lock will sit against the barrel before the barrel is inlet. Sizing up the situation by just holding the lock up against the bare flat of the barrel. that way allows you to determine the highest point the touch hole may sit without causing conflict. This is important. The proportions of some locks and barrels are such that they just won't work well together, and the problem can't be fixed by minor adjustments (like filing the corner off the mainspring.) This is especially the case with locks that have deep (thick) internal parts, or with locks that are too large for use with barrels of narrow dimension.

The touch hole does not have to sit right on the centerline of r the barrel flat. It is acceptable to drop it down a bit. We all like to see the fore stock follow the center line of the flat. But if you look at old rifles, smiths often made adjustments in the vertical position of the lock, even if that adjustment didn’t agree completely with the upper edge of the fore stock (which was centered on the flat).

This kind of vertical adjustment wasn’t necessary an afterthought, or a fix to a mistake. Sometimes it was an intentional part of the design. See, for example, this photo of an antique brass barrel (thought to be from the “third quarter of 19th century”). Note that the integral (cast in place) lugs have never been drilled—the barrel has never been fitted to a stock. And yet the touch hole was predrilled, and drilled below the centerline. Interesting, from a design perspective…

 

So my point is to note that a touch hole drilled a bit lower than the centerline is not necessarily a weakness. Especially if the touch hole is lined with a coned insert, or coned from the inside, then the influence on ignition may be negligible. The more important issue re touch hole location is whether or not the touch hole is drilled properly in relation to the pan. It cannot be drilled to high or too low in relation to the pan.

[Gaeckle]

..........looks your shootin' perfe3ct "x"'s...........

[Pete G.]

Take a close look at what is really going on. The energy from the mainspring is transferred from the part of the spring that flexes, for the most part the bottom leaf. The top leaf doesn't really add a lot to the process, consequently thinning/narrowing doesn't really affect the action a whole lot. Cock your lock slowly and watch the spring action. It will pivot around the anchor pin. The bend will tend to move down, but the portion of the upper leaf from the rear end to the peg will not move much if at all. I does little more than hold the spring in place.

[Jerry V Lape]

I have been following this thread because I had exactly the same problem going on at the same time - main spring making contact with the barrel.  Solved it the same way: filed a little off the corner of the upper arm of the mainspring.  Haven't yet figured out why I had the problem as I did lay the lock on the barrel in the position for the inlet and it had clearance.  Perhaps I rotated the nose of the lock upward somehow as I inlet it. 

[whetrock]

okay guys,
I'm gonna try one more time with the brass barrel image. here goes... take note of the low-slung touch hole, predrilled before the barrel was ever installed in a stock.