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Designing springs for locks.

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Matt Maier

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People with more CAD experience than I, what is your process for designing lock springs? I am working on designing a miquelet lock and the springs are proving to be the most difficult part.
 
I'd copy an old lock for the first try. They did the cut and try for you already.
 
That's what I am doing for the most part. My issue is that I can design the spring in its uncompressed state, but then it looks weird in the assembly. I might have to figure out how to design the spring as it would be compressed and assemble it that way, then I have two models of the mainspring. There's only so much I am likely able to do with the free version of Fusion 360.
 
I have no idea how to computer model a spring.

I have made a bunch of springs. "looks weird in the assembly" You mean on the computer? I would bet they could not model the spring properly in the software. The taper of thickness and width is important. It is like the parabolic action of a fishing rod. The actual mathematics of it would be quite complicated. I would speculate it involves calculus to model it correctly.

Perhaps you could make a virtual leaf spring with multiple leaves in you model rather than a tapered solid steel spring?

I'd make the real spring and try it. You may need to thin it, re-heat treat, reshape, or make a new one. I doubt a computer model will help you. Sometime you just need to cut metal.
 
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Hi Matt,
Looking at typical mainsprings on Spanish locks they seem very simple with no hook or spur. I could probably make one in an hour. The key is the bend is hammered flat and you need enough width to make the double tab that goes through the lock plate. I would use SAE 1075 steel and use pretty stout stuff. The metal must be heated bright red and the bend formed in stages to prevent cracking. When the spring is fully bent back on itself, there will be a bulge at the bend. Keep heating and pound the snot out of it until it is flattened. You can go back and open the bend a little if needed. The photo below shows the mainspring I made for an L&R Queen Anne lock. You can see how tight the bend is. I could easily file the bend to look like a Spanish lock.

dave

62aeNxa.jpg
 
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Hello Dave, you would be correct. Springs on Spanish locks do have simpler geometry than standard flintlock springs. Since its the heel of the cock that acts upon it, it doesn't need a hook to engage the tumbler, which is a part not present on the majority of miquelet locks.

One of my questions would be how would you clean the scale off the inside of the bend? Or is it even necessary to do so? Machining is my forte, I have never engaged in blacksmithing, which it seems some amount of it will be necessary in order for me to be really serious about lock making.
 
"looks weird in the assembly" You mean on the computer?

Yes, exactly it. I'm pretty sure there is a way to do it, but I am not an engineer nor are my mathematics skills any more complex than the shop math I make use of during the course of my job. Perhaps I need to try and look at this from a different perspective than that of a machinist.
 
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