rbernie
Contributing Member
The title says it all – what are the function tests that I should do to a new liner lock to verify that it's safe?
Function test a liner lock?
- Thread starter rbernie
- Start date
- Status
Many recommend whacking the spine of the blade forcefully on a surface to see if the lock with disengage and allow the blade to close, but that's risky unless you're wearing protective gloves and it doesn't represent use.
Wedge blade to hold it in place and grasping the knife twist back and forth paying careful attention whether the fingers or hand partly disengage the lock. You can test by gently pushing the handle towards the blade to see if it isn't secure. Don't just give it a single tweak and don't just use the same grip. Get the meatiest part of the fingers and hand on that lock where you'd unlock it and see if it gaps the contact with the tang. That's how I've gotten every inadequate liner lock to fail that has done so.
Look at the lock engagement to see if the lock goes past the engagement on the tang at all. That's going to eventually fail to make full contact and the lock will get sloppy and unsafe. Look at the angel of engagement and if the face of the lock is angled slightly so the tang "digs in" on the face of the liner lock so that over time it keeps digging in instead of digging out.
Look at the part of the lock that you use to unlock the knife. If it is prominent enough to protrude below the frame or it is easy to get too because of an overly large cutout in the scale then it will unlock on you.
Wedge blade to hold it in place and grasping the knife twist back and forth paying careful attention whether the fingers or hand partly disengage the lock. You can test by gently pushing the handle towards the blade to see if it isn't secure. Don't just give it a single tweak and don't just use the same grip. Get the meatiest part of the fingers and hand on that lock where you'd unlock it and see if it gaps the contact with the tang. That's how I've gotten every inadequate liner lock to fail that has done so.
Look at the lock engagement to see if the lock goes past the engagement on the tang at all. That's going to eventually fail to make full contact and the lock will get sloppy and unsafe. Look at the angel of engagement and if the face of the lock is angled slightly so the tang "digs in" on the face of the liner lock so that over time it keeps digging in instead of digging out.
Look at the part of the lock that you use to unlock the knife. If it is prominent enough to protrude below the frame or it is easy to get too because of an overly large cutout in the scale then it will unlock on you.
Good advice.
Along with my basic "don't buy cheap liner locks".
Even most inexpensive lockbacks will be safe. A cheap liner is an accident waiting to happen.
Here's an article about it, though of course hso covered most of these points. I'm not a big fan of the spine whack, but everything else is valid. I tend to feel for blade play on new knives without even really thinking about it, and if you use knives regularly, should know if you'll be able to use a knife productively just by drawing the knife, cutting something, and replacing it a few times. Also get in the habit of quickly checking the lock engagement and wear when you do your weekly clean-and-lube.
Along with my basic "don't buy cheap liner locks".
Even most inexpensive lockbacks will be safe. A cheap liner is an accident waiting to happen.
Here's an article about it, though of course hso covered most of these points. I'm not a big fan of the spine whack, but everything else is valid. I tend to feel for blade play on new knives without even really thinking about it, and if you use knives regularly, should know if you'll be able to use a knife productively just by drawing the knife, cutting something, and replacing it a few times. Also get in the habit of quickly checking the lock engagement and wear when you do your weekly clean-and-lube.
Side to side play may exist safely if small, but if you open normally by hand and there is any up or down play the lock isn't properly constructed and is unsafe.
Last edited:
As a general rule, this is what I do:
- ensure the position the tang locks up at is correct (different knives have different lock positions, but if the tang locks up too far or too shallow, that's an issue). Also ensure the tang is not locking up at a different position, because if the position of the lockup is changing, that is a potential concern.
- perform a light "spine whack" (I HATE using that term) test against the back of your hand or knee. I emphasize light because whacking the spine hard will, over time, ruin the lock and it will not tell you anything more than a few gentle taps against the hand. Obviously you want to hold the knife in a position that, should the lock fail, the blade does not close on your fingers.
- check for blade play by gently pinching the blade in one hand and the handle in the other. Almost all knives will have some degree of play, but if the amount of play is significant or if it is increasing, you may need to adjust the pivot screw
- ensure the blade locks up correctly with whatever method you use to open the knife - for example, if you use a very gentle thumb flick, ensure that the inertia used to open the knife results in the lock engaging properly
- apply a protectant to the locking mechanism designed to protect against wear - I find a good product will dramatically reduce the metal-on-metal wear that virtually all locking mechanisms are prone to
X-Rap
Member
- Joined
- Sep 23, 2006
- Messages
- 6,657
Here is a discussion about testing using the "spine whack" from a few years ago. It is a method I use and feel comfortable with in testing the overall durability of the lock.
http://www.thehighroad.org/showthread.php?t=484389&page=2&highlight=110+buck+knife+failures
http://www.thehighroad.org/showthread.php?t=484389&page=2&highlight=110+buck+knife+failures
Last edited:
A friend showed me the scars from some wicked cuts when his expensive liner lock knife folded up on his fingers. Ive since regarded liner lock knives as no lock knives in use. Theres plenty of good lock backs that fill my needs. Example and opinion of one and all that. YMMV
longspurr
Member
I believe a safe way to check the lock on a folding blade knife is to clamp the blade in a vice. That stabilizes the blade and insures it will not go anywhere. Then grab the handle and twist away. You can also modernly smack the handle part with the hand to simulate hitting the blade against something.
Since the blade is securely held by the vise I think your hand will be safe. NOTE: blade securely held by vice.
Since the blade is securely held by the vise I think your hand will be safe. NOTE: blade securely held by vice.
Look for full engagement of the lock and minimal "ramping" on the blade and lock. I don't like to look at the lock/blade engagement and see that the lock is barely engaging the blade and that the blade surface where the engagement takes place is ramped in such a way that force on the blade would tend to squeeze the lock out of engagement.
You want the lock to be sturdy. It won't do any good to have a solid engagement if the lock will simply bend/fold when stressed.
Make sure that the lock tension is reasonable. If it's too light, it will be too easy to disengage it unintentionally either with a tight grip or if the knife is jarred.
Hold the knife carefully so your fingers aren't in the way of the blade closing and tap the spine of the knife against something solid--maybe a 2x4 or some similar piece of wood. This is a pretty extreme test because it tends to jar the blade and lock out of engagement for an instant and then sort of squeezes the lock out of the way if there's a slanted engagement surface. I've run into liner locks where just a light tap on the spine would cause the blade to close even when the engagement looked good.
If the blade closes with the tap test, but the lock looks sturdy and the surfaces aren't too slanted/ramped, then you can see about increasing the engagement and/or increasing the lock tension. Sometimes you can salvage one.
You want the lock to be sturdy. It won't do any good to have a solid engagement if the lock will simply bend/fold when stressed.
Make sure that the lock tension is reasonable. If it's too light, it will be too easy to disengage it unintentionally either with a tight grip or if the knife is jarred.
Hold the knife carefully so your fingers aren't in the way of the blade closing and tap the spine of the knife against something solid--maybe a 2x4 or some similar piece of wood. This is a pretty extreme test because it tends to jar the blade and lock out of engagement for an instant and then sort of squeezes the lock out of the way if there's a slanted engagement surface. I've run into liner locks where just a light tap on the spine would cause the blade to close even when the engagement looked good.
If the blade closes with the tap test, but the lock looks sturdy and the surfaces aren't too slanted/ramped, then you can see about increasing the engagement and/or increasing the lock tension. Sometimes you can salvage one.
rcmodel
Member in memoriam
+1
I have only had one liner-lock fail in the last 30 years.
That was a Benchmade Mini-AFCK I loaned to my son.
( But, I make it a habit not to put spine pressure on folding knives, as there is no real reason too.)
I don't know what he did to it, but I fixed it when he came back whining about it.
I took it apart, and sprung the Titanium liner-lock further into the center line of the knife.
It's still going strong 20 years later.
rc
I have only had one liner-lock fail in the last 30 years.
That was a Benchmade Mini-AFCK I loaned to my son.
( But, I make it a habit not to put spine pressure on folding knives, as there is no real reason too.)
I don't know what he did to it, but I fixed it when he came back whining about it.
I took it apart, and sprung the Titanium liner-lock further into the center line of the knife.
It's still going strong 20 years later.
rc
T.R.
Member
I love my cheap liner lock by MTech. Yes it must be tightened up from time to time and the edge doesn't last as long as a BUCK but the shape and size are perfect for EDC.
TR
TR
Last edited:
Price doesn't determine the design aspects of a liner lock. As mentioned, expensive ones will fail. I've had that happen. On the other hand, the cheap - under $30 knife I currently carry is reliably safe.
What should be looked for in the design aspect is a liner leaf cut from thicker stock, with the pivot point as far from the blade toward the butt as possible. The longer leaf will have less cant when engaged and that is what causes the liner to walk out as the blade wobbles - it literally pushes the liner to one side working it out of engagement. A thicker leaf has more surface area and more friction, resisting that motion even more.
It goes to having solid bushings on the blade, too, not squishy Teflon liners that let the blade wobble. It's the motion that creates the disengagement.
What the angle of the lock is ground also affects it. Steeply angled lock ups can be problematic.
Any one of those items could be less than optimal and the knife perform well, but in certain combinations they consistently fail. I've got a Kershaw Boa that will not pass a spine whack or hold reliably in use - not a cheap knife at all. And the Camillus I currently carry, for less than $30, has never had a questionable moment.
Price means nothing. If it was truly a guarantee then the expensive knife makers wouldn't need a Customer Service department, because by the logic of price alone, it would be guarantee enough. The reality is less so. Expensive knives can very well fail, and making the mistake of trusting them without checking is where expectations get cut off.
What should be looked for in the design aspect is a liner leaf cut from thicker stock, with the pivot point as far from the blade toward the butt as possible. The longer leaf will have less cant when engaged and that is what causes the liner to walk out as the blade wobbles - it literally pushes the liner to one side working it out of engagement. A thicker leaf has more surface area and more friction, resisting that motion even more.
It goes to having solid bushings on the blade, too, not squishy Teflon liners that let the blade wobble. It's the motion that creates the disengagement.
What the angle of the lock is ground also affects it. Steeply angled lock ups can be problematic.
Any one of those items could be less than optimal and the knife perform well, but in certain combinations they consistently fail. I've got a Kershaw Boa that will not pass a spine whack or hold reliably in use - not a cheap knife at all. And the Camillus I currently carry, for less than $30, has never had a questionable moment.
Price means nothing. If it was truly a guarantee then the expensive knife makers wouldn't need a Customer Service department, because by the logic of price alone, it would be guarantee enough. The reality is less so. Expensive knives can very well fail, and making the mistake of trusting them without checking is where expectations get cut off.
A note on "squishy" pivots- self lubricating metal (bronze) is the gold standard once we step down from bearing, teflon followed by polyethylene follow. Bronze is far less compressible than the polymers.
Some pretty good tips in this thread. For me first thing I check is lockup. I don't like early lockup.
I don't flick my knives much in normal use but I do it repeatedly with any new Walker Liner Lock. Lets the lock face and the tang settle in to it's sweet spot. And I never do spine whacks. But Sal Glesser has said they do do it at Spyderco as part of QC.
I have never had a problem with a well made Walker Liner Lock.
This is a Military being used to push cut an oak sapling, shortly after I bought it.Lots of side to side tourque as I nibbled away at it. I just used body weight to bury the blade in as deep as it would go, then twisted/pulled it out, and repeat.
My Military's lock up after wearing in. Perfect in my eyes. Military on left, Emerson Mini CQC 15 on right.
I don't flick my knives much in normal use but I do it repeatedly with any new Walker Liner Lock. Lets the lock face and the tang settle in to it's sweet spot. And I never do spine whacks. But Sal Glesser has said they do do it at Spyderco as part of QC.
I have never had a problem with a well made Walker Liner Lock.
This is a Military being used to push cut an oak sapling, shortly after I bought it.Lots of side to side tourque as I nibbled away at it. I just used body weight to bury the blade in as deep as it would go, then twisted/pulled it out, and repeat.
My Military's lock up after wearing in. Perfect in my eyes. Military on left, Emerson Mini CQC 15 on right.
Just to clarify, I'm not talking about hitting the spine so hard that it seems I'm trying to break the knife or whatever I'm hitting. If it takes that much to make the knife unlock then I would consider it safe and besides I'm not comfortable beating the crap out of a knife I paid good money for.
The ones I've had unlock didn't require extraordinary amounts of striking force to achieve that. In fact, it's often surprisingly easy to get them to unlock.
- Status
