Mainspring at rest below lock mortice/plate. rectify?

[M. E. Pering]

With the exception of Jim Chambers locks, I have always had to tune an off-the-shelf lock for optimal performance, and even the Chambers lock need a little touching up.  This is one of the reasons I am going to start forging my own locks... It won't take much more time to make it myself as it does to fine tune those offered commercially.  Another advantage to a forged lock is that it is stronger than cast, though with today's metallurgy, the casting come pretty close in strength.  But the real advantage will be the ability to make a lock exactly the way I want it, and control the geometry of everything.

But in this case, ddoyle, I would do a bit of filing on that bridle.  I prefer that the notch in the cock hit the lock plate before the tumbler hits the bridle.  But as close to simultaneously as possible.  This way, once the lock is broken in, the slight peening that occurs will make it simultaneous, and I believe this might add to the life of the lock, with a bit less stress on all involved parts.  Just my opinion on how a lock should function.

Matt

[Bob Roller]

Having a tumbler to impact the bridle is a good way to bend or break the screw(s) that hold it to the plate
and that indicates either poor workmanship. The frizzen spring can act as a brake if it doesn't open prematurely and then the cock shoulder should impact the top of the plate.I would like to see one of these pretty little locks with the cock using the flash fence for a stop after 500 shots.Most if not all the old ones I have seen were in good shape due to lack of use,mostly cased sets,status symbols for the wealthy  and rarely used beyond the proof house. If I make any more flintlocks I will stay with what I know works and I have more than a passing idea as to what does.

Bob Roller

[L. Akers]

As stated in another thread, "commercial locks should be considered as kits" and need a lot of fitting and tuning up.  But back to your original mainspring question.  Consider that a lock at full cock has the spring exerting maximum force where it is least needed.  As soon as the sear is tripped the spring begins to diminish in power.  At the bottom of the stroke where the force is least is where it is needed to be the greatest.  This is why the spring needs to have some pre-load.  A spring with 0 force at the end of the stroke will not produce sparks.  True, you could make a plate wide enough to cover a fully relaxed spring but you would have a very clunky looking rifle. Good luck with your experimenting and your build.

[ddoyle]

Much thanks for learning.  First 5 hours into this lock complete maybe another 50 and I'll have something.

Cheers

[doug]

What no one seems to have said so far is that the mainspring uninstalled and which has the tip below the lock plate is what I understand the term "preload" to mean.  In other words, the spring , when installed has x number of pounds to thrust loaded onto it before you start cocking the gun and loading it further.  You could make a spring to replace the supplied one and which had an equal amount of thrust but it would have to be significantly thicker to achieve the same end.  I have had several locks which sparked markedly better after increasing the preload

cheers Doug

[Long Ears]

Well, one of the best lock makers in the world has weighed in here and I suppose if you have a better mouse trap then have at it. Kinda strange to ask for advice and then argue with it. Your lock, your money and your idea. Have at her. Bob

[mattdog]

Where is Mike Brooks to say " put the darn spring in the lock and stop worringing about it". 

[David Rase]

I would forget about what the spring looks like out of the lock and worry more about the spring when it is fully compressed.  Is the spring flat wen it is compressed, is the whole lower arm flexing or is it bending in the middle of the lower arm.  That is what will cause your spring to break, not the initial preload.
David
I couldn't help myself.  I just had to open up another can-o-worms.

[ddoyle]

Dave,

Thanks for the heads up on what to look for in a mainspring. much appreciate it.  I really gotta get educated on springs. Is the trouble you describe (not flexing equally) a function of the heat treating or of the springs shape and dimensions?

Re pre load: I see where this whole thing started for me. I was under the false impression that it would not matter if the spring tip moved a little or a lot as long as it was compressed when installed on the tumbler cam. I thought that a flat spring was going to have the same resistance to moving whether the pre load moved the tip 1/128ths or if the pre load moved it 1/4.

Obviously  I am wrong about that.  So now I understand that springs need to 'warm up' to the idea of being springy by gradually building up strength in the pre-load portion of travel (more the better).   

When I squeeze small v- springs with my fingers the force feels the same thru the length of travel Likewise a fish scale spring moves in a straight line linear relationship with the amount of force applied. I guess  flat springs are just different and the force it takes to move them does not graph as a straight line but as a curve.  (so the spring is kind of a cam and the tumbler has a cam........no wonder matchlocks seemed like such a good idea for so long )

 


Doug, thanks for your constructive post. I appreciate the thought out input. cheers.

[ddoyle]

Yep. My confusion was that I did not understand the difference between a linear and no linear spring.
Definitions

A linear spring is one with a linear relationship between force and displacement, meaning the force and displacement are directly proportional to each other. A graph showing force vs. displacement for a linear spring will always be a straight line, with a constant slope.

A nonlinear spring has a nonlinear relationship between force and displacement. A graph showing force vs. displacement for a nonlinear spring will be more complicated than a straight line, with a changing slope.

It is the changing slope that we move along in the pre load phase. crystal clear now.