It seems anymore that not a day goes by that I don't get at least one email, private message from a knife or blade forum member or a phone call from someone with a knife question and many times the main question and concern of the person contacting me is regarding the lock on their folding knife. My advice is usually simple. Whenever possible I suggest that you contact the manufacturer or maker directly about it. Sometimes the things I have said in passing regarding certain types of locks have been misinterpretted to indicate to the person that hears it later from someone else through the grapevine by a third or fourth party that I am not a fan of one company or another. I assure you this is not the case. If its a folding knife I'm a fan.
Its your fingers the lock is supposed to be safe guarding and in order to help that along and make sure it does just that requires some effort on your part to insure your safety when using a locking folding knife with a razor sharp blade. I might add that this goes for anyone and any knife regardless of who made the knife you carry. So, if you are going to carry any folding knife that locks and especially if you intend to put your knife to 'hard use' at least test the lock on occasion to be sure its doing its job securing the blade as it should and learn a little bit about the lock you prefer so you know enough about it's characteristics to be aware of just what it does under different loads of stress from twisting type lateral stress to vertical spine pressure on the tip of the blade. Periodic tests are OK now and then for your locking system on a folding knife but more importantly maintenance and examinations are highly recommened for folding knives, particularly if you carry it in a pocket deep where it rolls around among pocket change and keys down there where it can end up collecting pocket lint. So, to properly insure they are functioning as they should I'd suggest you occasionally test it and clean it. Just a simple thing like pocket lint can change the nature of how safe or unsafe your lock can be so be alert when using one.
Contrary to popular belief you can test your folder lock without spine whacking it and I recommend you do test it in other ways than this. My personal opinion is that spine whacking is bad and spine tapping is better but more on that in a few. Many people believe spine whacking does not harm a folder but believe me when you have seen the insides of as many knives as I have seen you know it can take its toll on them. I see the knives up close exposing the parts where I can separate out each individual part to examine it closely under magnification. This is when I can tell that spine whacking does indeed take its toll on a folders locking mechanism and even sometimes on other parts in the system. The lock mechanism on a folder is made to exacting tolerances. If a part in a folding knife is just a few thousanths off things can really get out of whack in how it functions. Believe it or not spine whacking does appear to be responsible for sometimes knocking things out of whack in some knives. Folder lock mechanisms are not big bulky pieces of machinery folks. In many cases you can damage a folding knife's locking system the very first time you shock it with a spine whack. Of course you can easily do this and not even realize it a lot of the time. So what other method should I use you ask. Ok just keep reading.
In the past I have at various times been asked to be one of several "field testers" for some knife manufacturers and they have sent me knives to evaluate and get back to them about after testing. Seeing a knife taken apart brand new to examine it and comparing it to one spine whacked repeatedly I can see things like sheared metal, indented spots on the locks, rounded off edges that used to be crisp straight lines or nice sharp corners and even hair line fractures that are all from that sudden tremendous shock to the locking system. So if you are in the habit of repeated spine whacks to make yourself feel better about your lock performance you may find this very well worth your while to read. Honestly after hearing from some of you that have sent me knives for repairs I'm surprised your locks have worked as well as they have after suffering regular intervals of this type of sudden shock and abuse to the small parts in the lock system. You may not be aware of it but it is highly likely that you have voided the warranty of your folding knife also because of abusive treatment. Spine whacking is not considered 'normal use' so keep that in mind when you think to do that to your knife.
Granted some folder lock designs seem to suffer more from this type of sudden shock than others. There are many that suggest a 'tap' vs a 'whack' in the industry and although I do a tap myself on my own folders from time to time the real problem I have with even suggesting a tap verses a 'whack' to the spine of a blade to anyone else is that the definition of 'hard' or 'soft' or 'tap' or 'whack' is so subjective from one individual to the next that I'm sure some will still end up whacking the blades spines not meaning to, all the while being fully convinced that they are simply tapping it. For the record all lock types can show signs that this test method is not good for them at all, particularly when repeated. So as a caution I would suggest you not make a habit of doing this test to your lock.
I recommend a simple spine 'pressure test' putting the blade under load while your hands and fingers are clear from the path of the cutting edge. You can see me holding a folding knife in the picture I've enclosed here below in the first link pasted at the end of this writing. This is the way I test my locks. The first thing to do if your lock defeats from this test is don't panic. The main thing you are doing with this test is discovering how the lock behaves under load. Does the blade move vertically at all to where you can visibly notice it moves away from the stop pin? Does it feel secure? Does the lock slide toward release under load or is it rock steady? Things like this are good to know. Get to know the folder you carry and how it behaves now under controlled circumstances so you can know when to be on guard in normal uses and gauge if it will work for you or not. In the event that your lock does defeat contact the manufacturer or maker and discuss it. I'm sure they'll agree it is not normal and want to see it and since you have not abused it to find out how it performs you will be fine for a warranty. Steady spine pressure is a normal occurrence in the hand when using a knife.
I find it risky to mention one particular lock type here but its hardly possible to talk about lock defeats without mentioning the most frequently seen lock type in the folding cutlery industry. That of course is the liner lock. If you have a liner lock barely engaging the blade and you intend to hard stab it into a phone book to show off to your buddy I'd suggest you think again. I know at least three individual knife testers that quit hard stabbing liner locks or even testing them at all in some cases due to the fact that they can be very unpredictable from this kind of use when new. A liner lock is one that you need to break in good before you can drop your guard using it this way and even then be very careful using one if you didn't give the blade a good snap to open it. The liner and frame lock needs to engage properly to be effective and safe. Just like with a lock back design where pocket lint can jam in the lock notch and make the lock ineffective the liner lock can also suffer from things getting jammed in there to block it's travel to secure the blade opened. Pocket change and keys can get down inside there and cause blockage just as easily as jammed up pocket lint.
Its also worth noting that many makers build liner locks on purpose with very little lock engagement when the knife is new. This is to allow the lock to break in slowly because we all know that eventually with use the lock will wear and move in more to self adjust for wear, which is what it is supposed to do but many users of the knives do not realize how precarious and easy to defeat many of these new locks can be when they barely engage the blade they are assigned to support. Further still, many users do not realize the risk of not giving a new lock, or even an old well used one for that matter, a good snap to open the blade to make sure the lock comes out and engages the blade well. These things can be dangerous folks if you do not understand them. So until you get them broke in and understand how it works you may be unknowingly risking your safety by not educating yourself in advance. Most accidents are from user error, not a faulty lock. When used as they are designed the locks most often do just what they are supposed to do. So, don't be stupid or too proud thinking just because your favorite maker or favorite manufacturer built you a knife, or just because you saw it do this in a video DVD that it means the knife in your hand is perfect. First test it, and then use it with common sense.
Now lets discuss the test. Here are the test methods I prefer. The first test I always do is this one. I recommend standing with the knife like you see me holding one of my favorites here in the first link to a picture I have pasted below. But, pay special note here if you have a liner lock. I also recommend you make sure the lock on your folder is getting behind the blade well at least to the full thickness of the liner material itself before doing this test with a liner lock. If you just took the knife out of the box and the lock is not even coming out to engage the blade all that well yet because its not even broken in yet, skip this for now and come back to it later when you've broken it in. With liner and frame locks that have thicker slab type locks its not necessary to wait until the lock comes out to fully engage the blade. In fact on many of these that could be many years before they do that if ever. So most of those unless they are just barely engaging at all can be tested fine using this method. I would caution against spine whacking any lock that is new and particularly one that is just barely engaging the blade. Doing that could shear parts of the lock face and not only void your warranty but cause serious damage to your fingers or hands and maybe even cost you a lot of money for sutures. Again, remember always that these things are sharp and serious and you need to use common sense.
Hold your knife so if the lock defeats you won't get cut just as I'm doing here in the link. You owe it to your fingers to know not suspect or blindly trust that the locking mechanism on your folding knife works as it should. You don't have to cock your wrist as I did here in this photo. I'm just doing that for my wife to get it in the shot easier. Hold it with both hands and using your strong hand with the blade resting on that index finger knuckle simply push up on the spine of your blade holding the body tight so its steady keeping all body parts clear in the event the blade snaps shut. If you feel it is more comfortable to hold the knife with the lock sideways or up or down from the way I do in this picture and simply push down on the spine rather than up then do that. Its the same test in the end and it really does not matter which way you put pressure on the spine of the blade. The idea here is to load the blade. Sometimes if I have a blade to test I'll put on some gloves to make it easier to really muscle it.
The second test I will do on rare occasion is a spine tap by tapping the blade on the toe of my boot or palm of my gloved hand. As I have said many times, this tap method is an entirely different test than a 'whack' on a hard surface. A tap represents to me more of a duplication of a 'real world' use of what can happen on rare occasions when using a locking folding knife. Lets say you managed to wedge the tip of your blade really well in a log and had to pull hard to get it out and accidentally just tapped it some into a soft or hard object behind or to the side of you from the momentum of your pull out. That is a real world tap. So, a single tap that can be sharp is all I recommend and I hesitate to do that as a habit. The biggest differences for me between a tap and a whack is the repitition and the force used. However, there is more to it. A single tap or even three light ones is far less damaging than ten hard whacks or even more to the spine of your locked folder. Spine whacking a liner lock hard can indent your lock from the much harder blade forcing itself into the contact suddenly and can lead to both sticky locks, vertical movement of the blade and increased movement across the tang contact we makers call the interface. This contributes to wearing out your lock and in the worse case scenarios it can lead to the lock leaving the contact on the blade altogether or trying to by crossing clear across the interface and wedging into the washer space area on the non locking side of the folder. In the event the washer is thick enough to allow the liner to fit in the space between the liner and the blade from too much lateral blade play in the pivot you could wedge it in there and get it stuck.
So, regarding taps. Once you have tested the knife this way it is not necessary to continue doing this test if it passed the first method and a single tap or three. You know that the lock is good. Now use it and more importantly maintain it and keep it clean. Use the first method periodically to make sure nothing has changed. Also, and once again to be sure this sinks in, never tap or whack your folder if the liner lock is barely engaging the blade to secure it. This can not only damage the lock permanently by possibly shearing metal beyond repair or indenting it terribly but it can allow the blade to fly shut cutting whatever is in its path. I would also say in closing that its not a bad idea to test any locking type this way whether it be your trusted lock back, frame lock, Axis lock folder, or any lock type in between.
Here is another link to liner lock and frame lock information on contacts.
In this thread I have linked below I made several post that can also tell you a lot about the pros and cons of either a liner or frame lock as well as what I look at when buying one for myself.