About Thin Lock Cuts (bull pivots and thin locks replacement post for lost corrupted 2009 post)

Shown top is a production Emerson HD7 mangled at the point most all frame locks fail when stressed, (if they are built right) showing what happens when one gets stressed to the point that something has to give. There is a large variance from company to company and from knife to knife in location of the lock cuts and how they are done but one thing they all have in common is that they are taken down pretty thin at the lock relief where we makers bend the lock to put spring in it. Many people question why and have written me asking for comment on this over the years. Pieced together below are copy and pastes from many of those answers which is part of why there are different print sizes from different forums formats.. Anyway, the reasons for lock cuts are worth review. One could say that this aspect of the frame lock is sort of a controlled burn, so to speak.  Being a field tester for several cutlery manufacturers at times I have had some pretty neat experiences from various testings I was asked to do on various models either already being produced or being considered for production sent to me as a proto-type to give feed back on first. Please note I don't mean to imply that Emerson was one of these companies by showing this photo. EKI is one I have not tested for but as you can see looking around my blog or forums I'm certainly familiar with them. This photo simply demonstrates my point quite well.  For those companies I have consulted with some models make it to production based on feedback from various field testers like myself, selected for whatever reasons by some of those behind the scenes folks that keep coming up with all these fine new knives for us nuts! At other times testers catch things missed that are corrected before it is produced and made available to the public. 

During testing I've done, some very thin cut frame locks collapsed like that top picture or worse at 65 to 68 pounds of free weight hanging on the end of the knife. None tested made it to 100 pounds. Many of the locks just jump off popping free allowing the blade to start to close after a certain amount of weight is on there. Some liner locks actually hold more  weight than frame locks done like those in that picture when they do hold. A strong liner lock will hold 100 pounds. A strong liner lock like one in stainless steel .080 thick may hold 130 pounds but even that depends on if it has thin lock cuts, no lock cuts  and many other factors including the pitch angle and contact 'type' for the lock where it mates to the blade when opened.  Forgive me to add a suggestion comment and some thoughts on lock cuts on the outside vs the inside. 

In my testing it doesn't make any difference if the lock cut is on the outside or the inside and seems to have little to no say in how the lock behaves. I've read the theories from some on this supposedly being safer one way over the other.  I even believed it for a time but honestly, this theory of directed energy by where the lock cut is does not pan out in testing at all. I challenge anyone to try to prove that wrong. Primary responsibility for a lock sliding off the blade under pressure on the spine is due to a poor lock contact not where the lock cut is located. At least testing seems to prove this as both will slide off if the contact is bad, both will do what is shown above when done correctly and both seem to be about as thin for the final take down thickness. I will add that in my opinion lock cuts on the outside on frame locks are often times problems for more than a handful of users due to those deep lock cut sidewalls snagging and hanging up on pockets when extracting the folder from the pocket. I'll tell you what also, since this has come up since originally posting here on this. I love my Hinderer XM-18 3.5"  as much as the next guy but the outside lock cuts are what bang up my pockets sliding the thing in and out of my pocket in tip up right hand carry. Its not the clip doing that damage to my pockets over time. Its the outside lock cuts going bumpity bump over my pocket each time I use the folder.. 

Being that I make replacement customized pocket clips this puts me in a unique position in the industry to hear about this from users I guess as this would be why they contacted me and that is just how I discovered this about the lock cuts even being reported to cause folks to drop their knives at times by holding onto the pocket so firmly from these lock cut snags.. I say it is my opinion because my sampling of the industry is small and it is debatable if it a true representation of the larger portions of knife owners but it is likely there are others out there that have noticed this and never said anything. I say it again just for the record, that's my opinion. 

For me putting a lock cut relief area milled on the outside on a frame lock immediately means tip up carry right hand is likely not a good option for carry unless you are mounting the pocket clip on the non lock side of the folder you are building. Of course if it is a left handed folder this reverses on this.  These deep square edged lock cuts with distinct corners done on the outside like those typically seen in the Strider PT or SnG and SMF series as well as others being offered from other manufacturers and makers do catch pockets and it is primarily a problem for folks when the pocket clip is set for tip up carry as the preferred method for carry. The culprit is the 'pinch' as I call it where the clip forces the pocket rim down in that lock relief cut where it hangs up the pocket rim/seam in that cut out milled out area. Granted on some models such as the very tactical SMF folder it could be argued that this snag feature is a built in aid to keep from losing the folder when out there crawling around on the ground or hiding in fox holes. For the smaller 'non military', 'non national stock number models' such as the civilian models I see no reason to do the lock cuts on the outside when you consider the epic damage they can do to a pocket! Add in textured G10 and a tight pocket clip and you will be needing new pants due to the pocket wear when nothing else is wrong with them and in record time...  

In some cases unless you pull the clip stem at the lip getting it up off the folder to reset the clip tension setting to make it grab pockets less this snagging is enough to make one complain about it and even cause them to drop their knives when trying to pull them out to use them. I've had emails over this from users and heard the complaints and had the questions from users over the years asking me to either take down/reshape lock cuts on knives they own or replace/relocate clips etc etc. This question about fixing this issue does come up with lock cuts on the outside. To date I've had this question over the Strider PT the most. I've had others once or twice and several custom knives with deep lock cuts have been sent to me for clips utlizing the pre-existing holes since I refuse to modify anything custom or even work on it when the maker is still around.  


I can tell you that these beefy super thick models with even deeper more profound lock cuts with squared off deep side wall edges and a clip sitting right over that cavern is a snag waiting to happen lets put it it that way. I'm always puzzled by this and I see plenty of frame locks I like other than the lock cuts being out instead of in. If and when new makers ask me I tell them quite clearly if it were me, knowing what I know now I'd never do a lock cut on the outside on any frame lock and if I did it would always be done with sweeping half moon shapes tapering gently as opposed to deep sudden squared off cuts, particularly if there is a pocket clip mounted nearby that cavern. These type of cavernous squared off lock cuts are the ones usually responsible for customer complaints to me when they want to know if I can build a new clip to sit cocked such that it is away from that cavern hole lock cut or reshape the existing lock cut so it is not such a drop off that has a distinct corner.  

40 days previous to this photo this was a thrift store pair of jeans I bought without a mark on them. The only knife these pockets have seen is this Hinder XM-18 in it now for this pic and the smaller version of the same as I have both. The clip did not do the damage to this pocket. Tis the lock cut on the outside. Most of damage and chewing up is on the inside. I could cite example after example of this and I bring it up because people are always blaming the clips not the real culprit! 

For most on the Striders its a matter of lifting the clip so it won't grab pockets so much and this seems to eliminate the pinch snag from the clip catching the rim of the pocket seam in that lock cut. Problem solved really only to create a new one for some. It is really a matter of which is the least concern. Losing the knife from a lose clip tension or dropping it from a snag?  I've owned several PTs myself and rather like the model even if it does have this issue at times for some users.  For others the pinch still happens enough to frustrate them and clips are relocated or they move to a new knife model retiring or selling off the old one.  I rarely flip a clip to tip up carry when it has lock cuts on the outside that are squared off to snag a pocket. In my experience it can just be a time consuming job with a lot of trial and error to try to smooth it all out to make it work cleanly. Anyway, this hang up or snag of the clip issue is also the sole reason I do all my lock cuts on my own frame locks on the inside only. Unlike other makers my 'default' clip position unless specifically asked otherwise is always tip up right hand carry.  

Other than these things I see no real reason why the location of the relief area milled or cut out to thin the lock has any effect on how the lock should behave if it is correctly built and properly mated to the blade. Many makers do some of their knives with lock cuts on the outside on some and the inside on others such as Ken Onion for one example, but I feel it is likely more just playing with designs and different aesthetics than concern with how it makes the lock behave under load due to how the lock cut may direct or affect the lock.  I can't help but think that if Ken believed for one second that one way was worse than the other, or less safe, or more prone to failure of the lock that he would simply not do the one he didn't believe in and only do them one way. So, basically some of the greatest makers in the history of folding knives do their knives both ways indicating to me by the mere fact that they do both inside and outside mill relieved areas sometimes even on the same models to thin the lock means they see no issue either way in their testing as well so I'd say its a non worry for whether your knife has a lock cut on one side or the other regarding safety other than the fact that it has been reported to cause one to drop their folder a time or three to me.   Hope that covers it.

Now back to the picture opening this thread. Contrary to how many readers may feel about that picture above, that my friends is a design that deserves praise for defeating the way it was engineered to go. That HD7 above did its job and so did the designer/maker of the knife. I doubt any sutures or ER trips costing great amounts of money were needed with that defeat. We should all pray to be so lucky should we be the on the unfortunate end of a folding knife lock defeat ourselves one day. While we can all agree it is sad to see a great knife get mangled the fact is the user is still intact and that is what you ultimately hope for when and if this occurs. Being that this above knife is titanium it is quite possible that it is fixable if the titanium did not tear or stretch anywhere during the event that caused it so, with some heat from a torch and a reset of the lock memory that knife may be repairable. Only when they kink bad did they deform beyond repair. Had that been stainless steel it would surely have been ruined. Titanium gives the knife a chance to come back to life showing the amazing durability it is known for. 

How and when a lock fails just depends on so much including the length of the knife tested and the blade length, lock thickness, lock material the lock contact and more like the quality of the materials used and of course what you are doing with it when it happens. As you may have figured out that 100 pounds ain't much weight compared to many of the locks we all see these days being tested on youtube using different lock types. Triad locks by Cold Steel for example will hold two to five times that weight listed above in the same tests and fair better in about all other tests as well from spine whacks to overstrikes and more but does that really make them better?

There are other advantages to frame locks in that the hand helps the lock to absorb some of that shock it may see in use that cannot be duplicated to appreciate when doing static load (free weight hang) tests and in the hand the frame lock can and does do an awful lot of hard use jobs. Even a frame lock with the contact worn such that there is clicking from the up and down blade play from the wear does not prevent the knife from being used and even used hard. Its still my personal favorite type of lock because it need not hold a house on the end of the knife to be useful guys. For one frame locks are usually thinner in the pocket carrying easier even when extra long and they are open designs and as a result they fair better in muck than other designs!

Don't let it sway you from a liner or frame lock just because this can occur. Its still a very good design for most all things we do with our knives. Do we have to take the lock cuts that far down in the frame locks? No we don't. I personally wish makers or manufacturers offered some kind of tough use option or "He Man" option of their own to allow one to get a knife a bit stiffer and thicker. Its too much to ask though. Instead you just have to find a maker willing to work with you on that aspect of the folder. I was one of those makers until I quit doing the rebuilds and really I've darn near quit making knives at this point with all the clips and pry bars I get asked to do. When I did more knife work I've sold some frame locks like those few pictured here all done so the lock relief area was left thicker. Some folks have returned them later for me to thin more with more profound lock cuts so they were not so hard on thumbs when they operated the lock. Its not for everyone to leave the lock cut thicker. With lock cuts left thicker comes a host of other things.

Done with cuts left thicker it will not be a flipper blade unless you licensed IKBS which is a patented ball bearing type set up for the pivot. The detent ball really works and holds the blade closed well when the lock is stout because when the lock is stout the spring tension is too and sometimes the spring tension is such that you can really feel and hear the ball on the blade as you sweep the blade opened and closed and other times the lock is so stout that if you are the type that likes to flick your knife open and closed a lot its just going to cause pre-mature carpel tunnel and a really sore thumb or a really big callus if you keep it up.You'll also notice flattened detent balls on the lock a lot quicker when the lock is done this way and on some the pressure tension from the lock is so strong it off centers the blade when closed! This of course can be controlled some by 'how' you spring the lock because as we know even a thin lock cut frame lock can still be set to have stiff detent tension and hold down but this can be played with in various ways like how deep the ball goes in, and the diameter of the ball used in the lock and even where and how the spot hole in the blade is done to allow the ball to catch and hold it closed well enough to defeat gravity. For those reading that don't know what a detent ball is, it is that little ball bearing seated in the lock inside that sits on the hardened blade during the entire rotation as it pivots. If you look at the open shot of the Military lock in this thread you can see the ball bearing there in the corner of the lock. This ball is your anti-gravity device to keep the point of the blade down safely during carry on these types of knives.

My point before drifting off to detents was that if you were to spring a thicker model the same way as the thin cut models the difference in resistance is where you note serious difference. Hard to explain unless you make them playing with things.  Detent set tension has to be adjusted to make a thicker lock cut and as a result it is quite challenging to find that happy medium where the action of the blade, the release from the detent grab to open the blade, and the detent hold down all line up to work well enough to please your customer. My Demko frame lock that is about ten years old is like that and has been that way since I got it. It has some thick lock cuts probably upwards of .080 each for the final thickness of the slab on the double relief area. This is a stout folder and a good example of about as heavy duty of a frame lock as you would be able to get your hands on. 

 As for why we don't see thicker mill relief areas on frame locks? Well, its my guess that it boils down to pleasing people; as makers and manufacturers have to please a lot of folks. Its better if the action is easy and smooth and that's what everyone wants or they'd complain about it. So these makers doing a lot of frame lock folders or thicker liner lock type folders as well as the manufacturers trying to appeal to a large audience do what they feel is needed to make it strong enough to serve the owner, yet weak enough to be easy to use with comfort once the knife is broken in properly. It doesn't happen often where one fails or gives any trouble such as shown above. In fact many frame locks routinely take a pounding daily from their owners so they still do quite a bit but it happens once in a blue moon where one will fail.  

Try as one may to warn of it some react with anger at times when these things are pointed out. Its not often easy to look at your own favorites with the same eyes you use to view the not so favored knives in your collection. While it is true that strength is not one of the frame locks advantages it is strong in other ways and due to the infrequency with which we see any real problems with frame locks one must conclude they are strong enough. They do have limits though and just because they are not the strongest lock by any means does not mean it cannot still be your favorite. We just have to be honest with ourselves about what we see before us with each type of lock or system that makes up a folding knife. 

I've said before that if people would just for a moment take off the blinders spending half the effort examining the knives they love with the same eyes they use to pick apart knives they hate maybe then they will see more objectively for what is right in front of them instead of being blinded by bias, but unfortunately that is often times like asking someone of one religious faith to examine their own the same way they examine and pick apart opposing faiths. It just isn't happening. With some the bias is so strong that no matter what you tell them they don't want to hear even what amounts to common sense regarding their favorite lock type. 

Like any chain there is a weakest link and any chain is only as strong as its weakest link. In liner and frame locks that weak link is the lock. It doesn't matter how much you beef up the other parts of the system because they have no effect other than making that system more out of balance if the lock remains the same. You can stick a bull pivot 1/4" in diameter in there and you can put a bull stop pin 3/16" in diameter or larger and coat it with G10 scales and a super duty set of screws in it. But if the lock is still a gents liner lock in .045 thickness under all that coating its not advanced one bit more really because those locks are still the point where the knife will fail in say a free weight hang test.  Whats more it would probably fail at the same point it would fail if the knife had bone handles and bolsters and a 1/8" stop pin diameter with a 5/32" pivot barrel using that same lock! 

The truth is even a 5/32" pivot and 1/8" stop pin would still be stronger and outlast most locks in a free weight hang test of this lock type. Some companies have put bull pivots and bull stop pins in their knives ever since they realized they sell better in what I call 'wolf' clothing and while we can't ding them for some marketing to sell their wares we can see through it if we take time to look deep enough.

For what its worth even though a frame or liner lock can fold, kink, or bend and deform similar to the picture shown here these are not the most catastrophic defeats of a lock that one can experience and one could argue that makers create the circumstances such that if and when the frame lock or thicker liner lock type knife gets stressed to that point of something having to give then they'd rather it be programmed in so to speak so this is what occurs just as shown in the picture above of the mangled lock. Of course this relies on the makers skill at creating a perfect contact that allows this to happen instead of the much worse opposite where the blade is free. My contention is that in the hand the frame lock is very unlikely to defeat once gripped properly. This fact means that how energy is directed down the length of the lock is a non issue because with the hand there to block the lock it is going to defeat as the above picture shows whether the lock cut is on the inside or the outside. How is the lock going to slide off the blade when the hand pressure is pushing it the other way? It won't and cannot go that direction no matter where you put the lock cut. It will do exactly what the knife shown above did in the hand from a baton used on the spine of the blade to split a log. And while the lock did collapse it did it's job in the process. 

If you are going to have a defeat I guess what I'm saying is that this would be the way to do it as opposed to the way that requires sutures and costly tetanus shots and more after hours in the ER. Most of the time the blade is still opened and locked in this type of defeat albeit permanently with defeats of this type until you disassemble the knife but so long as fingers are not cut bad and maybe a bad pinch and a bruised ego are the worst of your problems followed by some choice words usually reserved for sailors its a not as bad a lock defeat as other types of defeats can be.  

As you can see if you browse my blogger from most of my old frame lock conversions I used to do a lot of my lock cuts to spring the lock just a bit different than most you'll see from other makers. For one mine are left thicker at the lock cut usually and as a result of a customer requests for me to do that. In fact it was people that bought frame locks from other makers/manufacturers and liked them but wanted more that led me to looking more into the lock cut. My first question to myself was why not do one without a lock cut so thin? Lets see what happens. At other times I was contacted by customers who wanted a folder converted from a thin liner lock that they could feel flexing in use. This turns a lot of people off to have a tactical folder they can see the lock flexing on and so the request was to convert these to a beefy frame lock. People don't like when the lock can be seen to slide down the contact drifting back toward release either. When they'd notice this they'd seek people like me out.  I simply filled customer solicited requests to get me into this. Everything I've learned is from my own playing with various thicknesses to find out and compare how each behaves.

 I've always felt the frame lock sides I did were stronger simply because you could feel the difference in spring resistance quite a bit and they certainly required more ummmph to release the blade. Then there is the visual thing. They do look the part of beefy and to some just the look of beefy is more important than whether it actually is any stronger which again plays into that bull pivot appeal! Boy they wore on the thumb and flattened a detent ball good and quick though when the lock cuts were chunky thick! So, I'd probably put a shallow lock cut not so drastically thin in a frame lock made for my own self. Some have asked me what is the best thickness for a lock cut in a frame lock folder or thicker liner lock folding knife. The truth is you could ask a thousand makers and get a thousand different answers I think. I like about .059-.060 personally. You can certainly get by with thicker though. 

Just because I did some of my frame locks with thicker lock cuts does not mean the same thing would not or could not happen with one of my folders as what you see in the picture here above. In fact it is likely it still would happen to one of mine and very similar to what you see in that picture above should mine be pushed to the same limits only by the time that happened to mine you would really have to stress the knife to double or more the force that it took to even begin to duplicate a situation like shown here. That isn't bragging. From my stand point it is simple physics.  Oh I realize my folders may not open quite as silky smooth with my lock cuts left as thick as some of them are but if thats what folks wanted they'd buy the knives someplace else instead of seeking me out.

For at least the few folks that have used me when I offered these conversions they wanted beefy and strong and were not too worried about a knife they sat around flicking opened and closed all day long like a replacement habit for nail biting. They pull the knife out when needed, it does the job, they put it back and they feel a little better about knowing that if they really lean into it that it should take a bit more before the lock ever reaches this point but its not changing the fact that the lock will still be the first thing to go for a controlled burn so to speak.

While I'm a big big fan of the Triad lock and all it brings, and I can say I own enough of them now I want to stress that frame locks are still one of my favorites among locks in folding knives. Even though it is most often not even as strong as some liner locks I find they are strong enough and to me they are much more reliable giving a sense of security once your hand is wrapped around it good. Of course some models prevent this hand wrapping of the lock by the position of the pocket clip so not all instill this confidence for me personally. I found some like the JYDII to be particularly appealing in frame lock due to the flipper being out there when its opened even if the factory clip does block the ability to get in behind the lock like you can on other frame locks. It is hard to imagine the blade coming back to bite you on one of these flipper models even in one of the liner lock models. In this case since you'd get a bad pinch at worse case scenario I'd have a good feeling carrying one of these even if a liner lock. I like knives with the choil built in because when you have a choil and the ability to position your index finger in front of the pivot it is also hard to imagine it defeating if your finger is there blocking travel.  

The way I have seen some lock backs break when stressed it seems obvious this type of lock would be a more disastrous defeat when it does occur. Based on how a lot of people use their Cold Steel folders it seems to me that when a Triad does fail that it is likely to have a great deal of force and pressure applied to it to make that happen. This could be quite disastrous in the hand and it would be more likely to really mess up the user as well as itself when it happens. So in my final analysis as much as I love the Triad lock, the frame lock design may in fact be the overall higher rated lock for effective and safe use in a folder compared to all others because its more in balance with the abilities and strengths of the human using it and when this type lock does defeat it is usually not as prone to complete disaster unless it is just made wrong from the get go. It is also debatable that the frame lock is better within the limits of what one should do with a folding anything! Perhaps if anything the Triad does set the bar a little higher for what a folder can take but with each step up there is increase in risk to the user and the way I see that it equates to imagining making a forceful cut through something and imagine you have great pressure on it and then it slips out of what you are slicing only to head toward the drapes your wife just bought! Now realize that the momentum of that cut is unstoppable! The drapes are toast!  So that is the point. The increased force brings with it that increase in everything else including increased risk to the user should something have to give. On a folding knife we see the result and perhaps this is the difference between knowing when to switch to the right tool (i.e., a fixed blade) and when to use a folder and when to know something is hype promoting some of the things they do with their products when in fact doing those things would void the warranty and in fact likely ruin the knife if not shorten it's usable life expectancy.  Anyway, that is my opinion on the matter. I hope that helps some of you.  

Lastly, its not really a weak design even made as shown above with all that titanium taken out of the thickness in the back of the folder. Can it be better? I guess so but think about it. We don't see a lot of reports of people doing this to their locks. To spend a lot of time worrying about the lock cuts is really making a problem where there isn't one.  Certainly it can be more balanced in the system that makes up the folder parts if one wants to play with thickness levels of the lock cut  yes but so long as you still design the knife and engineer it such that the lock would go first and hopefully just as shown above when it does reach that point of something has to give when the system gets stressed, I think the frame lock design is the most solid of those being used today. Which once again illustrates why I like the frame lock so much for all it brings to the table.  To make my point clear I'll say it again another way. You don't hear about defeats of this nature often enough due to the thin lock cuts to be a problem so therefore I'd say its really not a problem to concern yourself with. If however you feel you want one that just looks beefy discuss it with the maker and maybe they will compromise with you to give you some visual appeal with the lock cut done slightly differently on your folder. Never hurts to ask. Thanks for stopping by to read this drivel. 

Andrew Demko folder showing the off center blade due to .080 lock cuts . The lock is not sprung that much really.
What is interesting to note is that if you remove the lock tension the blade sits dead center. So as you can see by this visual it would not be for everyone because I know many knife nuts that would reject this folder based on the off center blade when closed. Thin those lock cuts some it would improve. Remove the lock tension so it is not sprung that much and the lock does not self correct for wear all the way in like you expect and you end up with vertical play. (up and down blade play)

Note the detent ball right corner of the lock and the iinside lock cut. The lock cut is thin but how many problems do we hear about with this or other thin cut liner or frame locks really? Not many. This idea of the pop in lock contact replacement is brilliant. Note also the stop for the lock built into the off hang of the insert which is made of hardened stainless steel. That keeps one from hyper extending the lock out the wrong way and does so quite well. Knife nuts can note the same thing on the Strider SnG and AR knives as well as all Rick Hinderer products. Hinderer patented and licensed this invention to Strider and others I think too at this point.