The contact is obviously of greater concern in the construction of an integral locking style folder.
There are liner locks better than others but all have similar tendency toward lateral pressure causing the lock to move. Because of this I tend to favor shorter bodied liner locks over the longer bodied ones especially if the liners are .040 or .050 thickness. The longer handles allow more leverage which equates to much more pressure, stress, and weight at the lock contact which can and does cause the locks to move laterally with just the right twisting torque and lateral stress, which has been testified to many times and is many times duplicated easily by simply cutting down a cardboard box.
In the time I've been a member of these forums I can't count on all my toes and fingers how many posts I've read of liner locks defeating on the owner while doing something as simple as cutting a cardboard box down. In my own testing some of the most reliable liner locks have been smaller gents folders no longer than 4" closed. The lateral stress factor which can move the lock off the contact is the weak spot in the armor of this style lock so generally if its a longer handled liner lock I'll avoid it like the flu due to the way they can allow you to really put a lot of undue stress on the lock contact. 65 pounds of weight down on the back of a longer folder is going to equal many times more weight at the pivot than that same 65 pounds on a smaller framed shorter folder.
When possible, especially in thinner liner locks I like to see a choil feature which effectively allows the index finger to get ahead of the pivot and prevent the blade from accidentally closing on your fingers even if the lock did defeat in use. For what its worth though I like the choil in frame locks and lockbacks and ball locks, and would go for that on any style folder.
I like a full spine in my liner locks when I can find it. Its how I made my own.
I built mine so that the blade stop and the rear spacer were all one piece construction of hardened steel. It added a bit of weight but it is negated by the fact that the screwed down spine helps to make the folder more rigid and less likely to allow the lock to fall prey to moving under those lateral stresses because it makes it much more difficult to cause the liners to flex in or out with a full spine in place.
I also like seeing a screwed down stop pin vs one just slapped in there to rattle like many do when done that way but in thinner liner locks I prefer not to see an open construction myself. This doesn't bother me at all with thicker stock liners because they can be very rigid on their own but .050 thickness or less still allows a lot of flex so as a second choice if the stop, and pivot and at least two other points on the build of the folder body hold it all together and the scales are thick enough to add some support I'd go for that.
My main pet peve with the stops just placed in there held in place by pivot tension only is that I have a ton of Emerson "rattles" which always confused me and drove me crazy. I never understood why a soldier would want a rattle in the field but many of the stop pins are placed so that they can in fact move laterally and slap back and forth with movement. Of course the rattling stops when the blade is on the stop pin but once the pressure is taken off you have your rattle back.
A good liner lock is a relative term subjective to the beholder I guess. To me a bad liner lock is one that has no detent ball or one that has a detent ball but may as well not have one because the one in it doesn't keep the blade down to prevent it opening from gravity. The detent should hold the blade to prevent any law enforcement officer that tests it from being able to hold the knife upside down and make it open from a flick type motion. It should hold the blade so that the point can't stick up out of the folder so much so that it can grab clothing or fingers by accident also.
I like when the detent ball grabs and holds solid but a little upward movement of the blade after the ball falls in place is deemed acceptable by most providing it is minimal movement and that what movement it exhibits does not allow the point to come up high enough to grab something with the point with the blade in the closed position and that it still keeps the blade from opening by gravity.
As to how or why Spyderco is good at it. Mostly its due to Sal to be quite honest with you. He tests the locks he uses, but he also seems well aware of the capability and shortfallings of the lock and other than the Military, which I understand he is in the process of discontinuing as a liner lock, I think he has shown that he is very careful about where he places the liner locks in his line up. Its worth mentioning that one of the reasons the Military is a good one is due to the added choil feature though and its also worth mentioning that the Millie as we know it is an older model. We've learned a lot about liner locks since it was first created.
Also, typically stainless locks wear a little slower than titanium ones and indent less so I would rate Spyderco's stainless liner locks as better than Emersons or other thinner titanium ones, but not quite as good as Kershaw's stainless which I feel are the best in productions, at least at this writing. This excludes Spydercos compression locks which in my opinion rate higher than the other style liner locks for both reliabilty and for strength, but I don't think you are asking about those type liner locks so I'll stick to the ones we are discussing. But speaking of that style lock, just the fact that Sal felt the need to create it in the first place speaks volumes to me about his true feelings or thoughts on the liner lock. Its just a guess but I'd have to say we probably see eye to eye on a lot of our feelings for the Walker style liner lock.
I can't say that just because I see one make more than I do another that it has anything to do with how other brands I don't hear about are fairing. Spyderco and Emerson owners are typically more loyal for some reason and are also more likely to invest some $ to repair their beloved companion vs other knives. I see it all the time. It may be that when the other brands wear out or develop a problem they simply get a new one but with Spyderco or EKI they'll contact me or someone else like me to get it back up and running.
What I look for are the things like I mentioned above. Track records tell some which you can trust and which not, but also the company making them. If they stand behind it and will also recognize when they can improve on it, thats even better. Again Kershaw stands out here due to the knives like the JYDII, and the NRG, the Zero Tolerance 0400 and 0200 among others that really shine for how well done they are compared to other competitive products many times for more money than you could get into one of these for. The thicker stainless liners are a big deal to me and speak highly of a company not just wanting to keep up with the pack but to lead them.
This is why I place Spyderco and Kershaw, and BenchMade tops in my ratings of companies in the knife industry because they are trend setters, innovators, and also constantly improving what they make and develop. I tell folks all the time that if you are going to invest in a liner lock to look at any of the ones that these three companies are offering and you stand a higher probability of getting a very well made reliable one you will be happy with. You can get some that will please you elsewhere but its a crap shoot at times compared to these three based on what I've seen. I don't want to leave Buck out of this picture though because they also make some higher quality liner locks and some of the Buck Strider folders I've owned have been top shelf. So I'd have to say that so long as you stick with these brands you should at least be better off than to go for something like one of the many knock offs and cheapo generic names sold elsewhere. Some of Cold Steels higher end peerless locks have impressed me also and these have proven to be quite strong.
As for frame locks. Any frame lock in my opinion is a step up from a liner lock in reliability so if it sits well with you and you like it I'm sure it will be fine. I like the Sebenza and use it as the reference to judge all others. So far none I know of and this includes even many higher dollar customs can come quite to the same level of consistancy and reliability as the Sebbie. Many try and some come closer than others but for the most part all still fall short of what is offered by Chris in the Sebenza time after time after time. I've had five Sebenza folders and each one so close and so identical to each other not just in looks, but in action, wear, weight, thickness, and lock contact that its unprecendented for consistancy of the engineering.
STR
