What the heck is "blade play" anyway?

Klesk

Klesk

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I've been carrying knives regularly for around 20 years now, and I have a bunch of good knives (my EDC rotation currently consists of a Sebenza, Surefire Alpha, Lone Wolf Harsey, SnG and Spyderco Police Model), so I'm not exactly a newbie, but I have no idea what "blade play" means. I've heard this phrase thrown about all the time, especially when people ask about a knife's condition, and I've heard others trash a certain knife for "excessive blade play". Does anyone actually know what this means?

In all my years, I've never seen a locking liner NOT move over enough to wedge the blade between the locking liner and stop pin; even in cases where the liner (improperly) moves all the way to the right, it still is holding the blade back. So I can't imagine that "blade play" means a blade that is not locked securely. If "blade play" means a blade that wiggles left and right when opened or closed, it's just a pivot tension problem, not a major issue (in itself; improper blade tension can mask a myriad of other problems). If "blade play" means a blade that moves back and forth along its long axis, then it is a problem with the pivot hole in the blade, I can't imagine this happening very often.

So, in the cases I've discussed above, either it's a minor problem (pivot tension) or it is a major QC issue (locking liner or pivot hole) which would seem to be very rare. Why then, does it come up all the time? Or is it something that I've missed?
 
I think when people refer to blade play they mean the vertical or horizonal movement of the blade where it is attached between the bolster of a lockback and between the liners of a liner lock. It doesn't necessarily mean the knife is not any good, I think it's more sub-conscious feeling that it's inferior. Of course tighter is better for safety.
 
Razorback - Knives said:
I think when people refer to blade play they mean the vertical or horizonal movement of the blade where it is attached between the bolster of a lockback and between the liners of a liner lock. It doesn't necessarily mean the knife is not any good, I think it's more sub-conscious feeling that it's inferior. Of course tighter is better for safety.
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This is correct. I will add also though, that blade play is possible in any folder no matter the lock type. Even Old slipjoints with alot of use can develop blade play.
-Kevin
 
to me, blade play is one step away from an accident, thats why I like fixed blades a lot, no lock failure. Even though locks are built strong now adays, I really am still scared of losing a few fingers.
 
blackhorde said:
to me, blade play is one step away from an accident, thats why I like fixed blades a lot, no lock failure. Even though locks are built strong now adays, I really am still scared of losing a few fingers.
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If you get a good folder there is almost no chance of having a lock fail on you. Spyderco's Martial Blade Craft rated knives take 200lbs. of pressure per inch of blade to create failure. Example: A Spyderco Lil Temperance would take 600lbs. of pressure to break the compression lock. (Now this isn't to say that you can't forget to clean the lock area, or not fully open the blade. :footinmou )
-Kevin
 
yeah, I heard they are really good knives, but no matter how good they say their lock strength is, I still get paranoid. I guess I've just been cut a lot. I agree though all folding knives do develop blade play after time, and heavy use. Especially when you're like me and like to flick em opem a lot. :)
 
blackhorde said:
yeah, I heard they are really good knives, but no matter how good they say their lock strength is, I still get paranoid. I guess I've just been cut a lot. I agree though all folding knives do develop blade play after time, and heavy use. Especially when you're like me and like to flick em opem a lot. :)
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Yea, they are good. Benchmade and CRK are two other great companies for modern folders. And yes, can't go without flicking! :)
-Kevin
 
Thanks for the discussion guys, but my original question is still somewhat unanswered as I haven't heard the mechanical reason for "blade play".

As I mentioned, I have a lot of knives and I have bought/sold/traded hundreds of knives, so I have handled quite a few. Also, I am very picky about my knives, yet I have exactly zero that show any kind of blade movement when locked open.

I can understand how a back lock can develop some slop over time, as the mating surfaces wear against each other, but a linerlock is somewhat self-adjusting. The locking liner will move farther and farther into the blade tang as the parts wear, but the blade should always be wedged between the locking liner and the stop pin.

The only way that I can see a linerlock developing any movement is for the pivot hole in the blade becoming out of round, or for the stop pin to be so deformed by hard use or flicking that the relationship between the locking liner and blade tang is affected. However, in the first case, that should be relatively rare, most likely a manufacturing defect, and in the second case, the locking liner should pick up that little bit of slack.

So now we're back to incorrect pivot tension adjustment, which may manifest itself in the form of blade movement, even when the knife is locked open. This, of course, is so easy to correct, why would it even be an issue?

I'm still confused... :confused:
 
Klesk said:
Thanks for the discussion guys, but my original question is still somewhat unanswered as I haven't heard the mechanical reason for "blade play".

As I mentioned, I have a lot of knives and I have bought/sold/traded hundreds of knives, so I have handled quite a few. Also, I am very picky about my knives, yet I have exactly zero that show any kind of blade movement when locked open.

I can understand how a back lock can develop some slop over time, as the mating surfaces wear against each other, but a linerlock is somewhat self-adjusting. The locking liner will move farther and farther into the blade tang as the parts wear, but the blade should always be wedged between the locking liner and the stop pin.

The only way that I can see a linerlock developing any movement is for the pivot hole in the blade becoming out of round, or for the stop pin to be so deformed by hard use or flicking that the relationship between the locking liner and blade tang is affected. However, in the first case, that should be relatively rare, most likely a manufacturing defect, and in the second case, the locking liner should pick up that little bit of slack.

So now we're back to incorrect pivot tension adjustment, which may manifest itself in the form of blade movement, even when the knife is locked open. This, of course, is so easy to correct, why would it even be an issue?

I'm still confused... :confused:
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Well, as hardheart says, lockbacks sometimes have vertical play. The reason for this is a small space inside the lock area. I'm not sure of all the technical terms... :o

As for liner locks, sometimes the blade is too thin for the handles, or the handles just weren't adjusted right, and this will cause lateral blade play. Meaning you can wiggle the blade the slightest bit side to side by pushing on the tip. Usually liner locks don't have vertical play. Does this help?
-Kevin
 
Blade play - Throwing knives at each others bare feet, :eek:daring the other not to flinch or move. We did this when we were kids....................
 
Well, I don't think that the statement in the original question is completely true. You can not adjust all blade play with pivot tension. Sure you can always eliminate side-to-side (lateral) blade play by cranking on the pivot screw (which is not possible if you have a rivet), however, in doing so your folder may become a fixed blade since you've wedged the blade so much that it doesn't move at all. To have a smoothly opening knife without any lateral blade play puts sever constraints on the washers at the pivot and on tolerances.
Up-down (vertical) play can easily develop if the stop pin deforms or the mating surfaces of a lock back don't mate. Once you have developed play, the stress on the pivot increases and under heavy use the play is necessarily going to increase to the point of failure, so it is a serious issue, which is why some companies void the guarantee if the blade has been flick open excessively. Fore-back play, I have never seen, and don't want to see ever. If I do, the knive goes right back to the ventor, period.
 
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