Lock back play?

P

padwan08

Joined
Dec 21, 2008
Messages
82
In another forum, some posters were wondering if play in a lockback was normal. Sal Glesser responded that lockbacks built for strength would inherently have a bit of play.

Is there a mechanical or engineering explanation for why a bit of play is necessary in lock backs? I've observed that my knives do have a slight bit of play. It doesn't bother me but I am quite curious as I have yet to find a technical explanation for this phenomenon.

Thanks!
 
The lock pivots around a pin, meaning its path is an arc. Therefore, you can't have a lock bar's "hook" sit perfectly flush in the notch of the tang.

However, my friend's SS Endura doesn't have any play... It's the only lock back knife I've ever handled that didn't have any play.
 
I've got a bunch of lockback knives from Spyderco (Endura, Police, Rookie), Buck (110, 111, 112), A.G. Russell, Ka-bar, Gerber, Moki, etc. Of these, precisely NONE of them have any noticable play, either vertically or sideways. I don't understand why there's an expectation of 'a bit of play' in a well-designed and executed lockback. I can see, over time and with heavy use, a lock can loosen up on a knife. But that's not exclusive to just lockbacks, it'll happen to any locking knife eventually if it's used hard enough.

Maybe it's a question of how some define the term 'play', or maybe the 'expectation' is that it'll EVENTUALLY develop some play? I don't know...

Edited to add:
Or, maybe it's a reference to play when blade is in the closed position? Many lockbacks will seem a bit loose when closed...
 
Last edited:
Obsessed with Edges said:
I've got a bunch of lockback knives from Spyderco (Endura, Police, Rookie), Buck (110, 111, 112), A.G. Russell, Ka-bar, Gerber, Moki, etc. Of these, precisely NONE of them have any noticable play, either vertically or sideways.

...

Maybe it's a question of how some define the term 'play', or maybe the 'expectation' is that it'll EVENTUALLY develop some play? I don't know...
Click to expand...

If I open my knife, put my pinky through the hole, and then tug multiple times, I can hear some small clicking, and under my thumb I can feel the lock bar shifting slightly. I can't see any motion, though.

I expect it because all of my lock back knives have it, and they've all had it since I bought them.
 
Perhaps it's a matter of degrees. When checking for 'play', I'll hold the handle in one hand, and pinch the blade between thumb & fingers of the other hand, while applying moderate pressure up/down. Then, I will look for visible deviation up/down or left/right, and then I'll 'feel' for tell-tale 'bumping' of the lockbar's tab against the forward & rear face of the notch in the tang. If I don't see any deviation, and don't feel that bumping back & forth, that's what I'd call satisfactory (no significant movement).

There's bound to be at least a tiny bit of lateral sliding/shifting of the mating surfaces of the lockbar & notch if enough pressure is applied, unless the knife is built like the proverbial battle tank (and priced accordingly, I'm sure). But again, that's to be expected from any type of lock, or any folder for that matter. It's two pieces, so it's gonna move at least a little.
 
Yes, a bit of wobble when closed I've noticed . But Bucks 110's,111's and 112's lock up like a bank vault . DM
 
THG said:
If I open my knife, put my pinky through the hole, and then tug multiple times, I can hear some small clicking, and under my thumb I can feel the lock bar shifting slightly. I can't see any motion, though.

I expect it because all of my lock back knives have it, and they've all had it since I bought them.
Click to expand...

Yeah, that's the kind of play I noticed in my blades. No side-to-side or fore-and-aft when locked open. Like I mentioned in the original post, it doesn't bother me, but I just wondered why it is built as such. Was sure the factory had a good reason.
 
With the FRN-handled Spydercos, they will flex a bit. They do have the nested, skeletonized stainless liners, but those are relatively thin nonetheless. When the handle flexes even a little bit, that'll allow a little bit of movement of the blade/pivot/lock bar.

I've been using one of the green G10 Enduras (which have thicker, full liners) and, as with the stainless-handled Endura mentioned earlier in this thread, it's quite a bit more rigid than the FRN models.
 
David Martin said:
Yes, a bit of wobble when closed I've noticed . But Bucks 110's,111's and 112's lock up like a bank vault . DM
Click to expand...

I have a 110 brand new that has maybe .001- . 002 thou. up/down play. It really doesn't bother me though. Whenever there are two,mated moving parts, there is going to be a extremely small amount , or it would probably be stiff to open. I'd rather it be a little loose than too tight. The up/down play I have is probably the lockbar interface with the blade notch. It's very small.
 
there has to be a certain amount of clearance between 2 moving parts in order for them to move freely.i have to laugh when i hear the term"zero tolerance" as zero tolerance=no movement.
 
You must log in or register to reply here.
Back
Top