What causes lock stick?

Bailey Knives

Bailey Knives

Knifemaker / Craftsman / Service Provider
Joined
Oct 18, 2004
Messages
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I have started making frame locks and I will have one that the lock works just as smooth as butter and the next that it sticks like I coated it with superglue. I think I am doing the same thing but I must be making a tiny error that has a large effect (affect I can never remember which to use). Any insight would be appreciated.
 
Can you explain tolerance stacking? The pivot is tight but i am using a threaded stop pin that could possibly shift. Maybe that is my problem.
 
Smoothness of the mating surfaces can contribute. Rougher surfaces will obviously stick more.

If you're using Titanium, Ti does tend to be a little "stickier" of a metal. A lot of makers mitigate this by either carbidizing the lock face on the ti side (depositing a thin layer of harder carbide over the ti) or using a hardened steel lock insert which won't stick/gall like titanium.
 
I have a carbidizer, but it seems to make little difference
 
Bailey Knives said:
Can you explain tolerance stacking? The pivot is tight but i am using a threaded stop pin that could possibly shift. Maybe that is my problem.
Click to expand...

OK real quick. Everything has a +/- tolerance. If you mix a blade that's +/- and a lock that's +/- it's all good.

Build a knife that's +/+ and a lock that's +/+ and it sticks. Make one that is -/- lock and -/- blade and it's loose.

So if you can lay out 10 blades and ten locks and mix them till you hit the ideal on all you're set.
 
What angle are you grinding your lock face at?
 
There are a couple things that can cause lockstick if you are carbidizing. You need to make sure the carb is even and then sanded down, I do mine to about 600-800 grit. You will need to let it set with a couple of hard lockups. If it still sticks check your lock geometry, not the angle but where is the lockbar face engaging the lockface. If you have a side groove, that's an issue you will have to polish out and recarb.

Too much attention is paid to the angles instead of what surfaces are actually interacting. Lockbar design is far more important in my opinion.
 
Bailey Knives said:
Thanks Pittknife, What exactly do you mean by "side groove"?
Click to expand...

Thats when your lockbar face is higher than your lockface, the angle that it meets should never be flush so you have your lockface digging into the side of your lockbar face. You will get a groove into the inside, near the detent ball. That burr & groove surface will cause lockstick. Only way is to remove the surfaces that are rubbing.
 
If I may... I never get the lock-stick thing. If the lock sticks, so be it. That tells me the lock is in place and it will just break in with time.
As long as that lock works, no worries!
rolf
 
Lycosa said:
If I may... I never get the lock-stick thing. If the lock sticks, so be it. That tells me the lock is in place and it will just break in with time.
As long as that lock works, no worries!
rolf
Click to expand...

There is lockstick and then there is real lockstick. Real lockstick you can't disengage without some type of tool to pry it open, in those cases your folder becomes a fixed blade without a sheath and cannot be carried.

Anyone that has made a folder out of titanium knows that real lockstick is a pita. Lock geometry is simple yet complicated to do right.

On higher end folders, it shows your knowledge, skill and attention to detail that you can make a very secure lockup while having little to no friction during disengagement.
 
Lycosa said:
If I may... I never get the lock-stick thing. If the lock sticks, so be it. That tells me the lock is in place and it will just break in with time.
As long as that lock works, no worries!
rolf
Click to expand...

I'm with you on this one. I have one knife that had some lock stick when I first bought it and after using it for about two weeks it smoothed out.
 
Sometimes relieving the end of the lockbar, near the detent ball (on the inside corner of the lockbar face) to limit the point of lock contact to the front corner of the lockbar, will help. Basically that is lessening lock contact and choosing specifically where it occurs. That's also a good way to eliminate "rock" feeling in your lockup, should it occur.

I have used flat ground, as well as 2" radius lock faces. I think a radius or hollow ground lockface sticks less.

Hitting the top edge of the lockbar face slightly with a scotchbrite wheel or belt, to deburr and very slightly round it, can help- and it also helps your lockbar glide more smoothly over the detent ball.
 
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