why relief cuts in framelocks/linerlocks?

[harkamus]

This thread got me thinking as to why makers put relief cuts on the lockbars of framelocks and linerlocks. I understand that the relief cut functions to allow the lockbars to bend, but that thread listed some makers as having been able to make lockbars without relief cuts. Of the top of head, I know Ray Laconico makes some knives without relief cuts in the lockbars. So, I know this can be done to a certain extent, thickness. Is it a function of lockbar thickness that dictates whether you can bend the piece? I really don't buy that. I'm sure you can apply heat and bend the lockbar without causing too much structural stress. At any rate, even if there was some stress incurred from bending the lockbar, I'm willing to bet that a lockbar of even thickness throughout the length is still stronger than a lockbar with a relief cut out. It's got to be a function of how hard the lockbar is to engage/disengage that dictates whether a relief cut is needed.

I'm all for overbuilt knives if they last longer. I'm jumping on the bandwagon that holds the notion that a lockbar is only as strong as the relief cut out. So what if you have a lockbar that's .15 inches thick if the relief cut makes that portion of the lockbar .05 inches thick? It just doesn't make any sense to me. I suppose a lockbar that's fully .15 inches thick throughout would be way too hard to close, but some knives have such huuuge relief cuts it's ridiculous. Seems to me that there should be more experimenting before milling away a big ass chunk of metal.

I wonder how fat a lockbar can be before it becomes too difficult to disengage.

 

[stabman]

I find that anything above 0.070" to be annoying to close. Doable, but annoying.
I think 0.060" thick is perfect.
I want a knife with a cut-out of 0.060" thickness and a lock-bar of 0.135-0.150" thickeness; the lockbar thickness makes for a nice big lock contact face when the tang angle is right and it wears in a bit.:thumbup:

 

[JNewell]

See the last paragraph in the recent post below.

Its not so obvious you are correct. Generally speaking it seems the only people/makers/manufacturers that say the thickness or the flexing doesn't matter are the ones that have made them that or still do. Honestly I don't know anyone that can really say they feel assured by the fact that simple spine pressure makes the liner lock they carry visibly flex under the light load.
Most feel that if it flexes that easy its unreliable. In testing thats not always the case. You can test some that jump right off the blade freeing it up and watch the blade snap shut hard and test others that the lock moves toward a tighter lock up. The nature of the lock type dictates that it begins self destruction from the first opening so its pretty easy in testing to develop vertical play. I've been surprised at the number of users that are not bothered by a little play and simply figure its just going to happen, and they've learned to live with it.

In an ideal world where the pressures exerted are always correctly directed at the stop pin the lock is of little concern so long as its staying put. As we know its not an ideal world and in use, particularly harder uses its quite easy to apply spine pressure to the tip of the blade quite easily. This is where a good lock pays for itself in my book. For liner locks I like at least a .050 thickness personally. These are harder to flex and quite noticeably more difficult to flex than a .040 lock liner. I don't feel now and never have agreed with anyone making a .040 or even a .045 liner lock and calling it hard use. Whatever though some do and thats fine. Apparently they work fine for a lot of folks. I wouldn't own it though.

Regarding the thickness at the interface or contact where the blade and lock meet: Most people just assume the entire lock contacts the blade. It does not. In fact the inside corner on the bottom third area of the lock should be all that contacts the blade. Actual surface area of the contact on a frame or liner lock can be pretty close to the same size on many knives. Only on certain models such as the already mentioned Sebenza where a concerted effort is made in the build quality do we see a more evened out larger foot print of contact over the same bottom third area of the lock contact. This I believe is perhaps the key difference between the Sebenza and other production folders. Chris has the best engineered lock contact of all production folders and while others will tell you they make their contacts the same way as Chris the truth is anyone can see at a glance comparing them side by side that only in theory are they the same. In practice Chris goes above and beyond to insure a more refined larger foot print area. How many Reeve locks do you have that stick and bind terribly? Not many I know. There is a reason for that believe me.

As for the cut out. Oh boy. Here I've already covered it so much in other posts I really don't know if I want to type it again. Most users would complain terribly if makers or manufacturers began making frame locks with thicker lock cuts. Only a person really wanting that extra strength and not really minding the extra baggage that comes with it (harder to close, harder to flick, more wear on the detent ball etc etc) will want that. Oh you can refine it down and find a happy medium with experimentation and by limiting the thickness of the slab you use as I did by using my .095 solid bar frame locks but overall a .125 or thicker lock simply has to have a lock cut of some kind to be functional or it will just be a failure to even try to use it. The only real draw back to a thin thin thin lock cut on a frame lock is when the folks buy one and decide to carry their frame lock clip less. Most clips act somewhat as a block for excess lock travel out the wrong way when closing the blade. This excess travel or hyper extension of the lock can cause it to lose spring tension. Its not reported often enough to worry with a whole lot but it has happened enough to make it a real world possibility.

STR

 

[harkamus]

I find that anything above 0.070" to be annoying to close. Doable, but annoying.
I think 0.060" thick is perfect.

First post I've read referencing different relief cuts. Just what I was looking for. Thanks!

EDIT: Interesting, so someone's actually gone as far as .95 inch without a cut out. Wonder how that feels to engage/disengage. This is something else I was hoping to find out by posting this thread.

 

[STR]

This thread got me thinking as to why makers put relief cuts on the lockbars of framelocks and linerlocks. I understand that the relief cut functions to allow the lockbars to bend, but that thread listed some makers as having been able to make lockbars without relief cuts. Of the top of head, I know Ray Laconico makes some knives without relief cuts in the lockbars. So, I know this can be done. Is it a function of lockbar thickness that dictates whether you can bend the piece? I really don't buy that. I'm sure you can apply heat and bend the lockbar without causing too much structural stress. At any rate, even if there was some stress incurred from bending the lockbar, I'm willing to bet that a lockbar of even thickness throughout the length is still stronger than a lockbar with a relief cut out.

So why do it? I'm all for overbuilt knives if they last longer. I'm jumping on the bandwagon that holds the notion that a lockbar is only as strong as the relief cut out. So what if you have a lockbar that's .15 inches thick if the relief cut makes that portion of the lockbar .05 inches thick? It just doesn't make any sense to me. I suppose a lockbar that's fully .15 inches thick throughout would be way too hard to close, but some knives have such huuuge relief cuts it's ridiculous. Seems to me that there should be more experimenting before milling away a big ass chunk of metal.

Hmm...makes me consider contacting my custom knife maker before he starts on my knife to see what he says about this.

You have to ask yourself, 'when is the lock strong enough?' And, could it be 'too strong?' Also, what are the pros and cons in doing it one way vs another. http://www.bladeforums.com/forums/showthread.php?t=808644

Based on the number of reports of 'real' problems with the frame lock, which are very few I don't think there is really a lot that needs changed. I mean lets face it they can do a lot of things, even with thinned down lock cuts and there may be some truth to the thought that the hand helps the lock to absorb many of the shocks that may cause it a problem if the hand was not there wrapped firmly around it but I can understand the desire by some to have stronger, at least enough to try to accommodate the requests. Personally I think people like flipping and flicking their blades opened too much to put up with a lock with that much spring pressure on it like it would have with a thicker lock cut model. I would agree with Stabman that thicker slab models over thinned down at the lock cuts to .070 or more can be at best, annoying, especially if you like flipping your blade opened and closed like its some kind of a worry stone habit.

 

[stabman]

First, I've read of a post referencing different relief cuts. Just what I was looking for. Thanks!

EDIT: Interesting, so someone's actually gone as far as .95 inch without a cut out. Wonder how that feels to engage/disengage. This is something else I was hoping to find out by posting this thread.

No problem.
I'd imagine that a 0.095" cut-out would develop some serious callouses on the thumb (let alone a 0.95").

 

[harkamus]

I would agree with Stabman that thicker slab models over .070 can be at best, annoying, especially if you like flipping your blade opened and closed like its some kind of a worry stone habit.

I don't have that habit. Once or twice here and there when I'm bored over the course of a week or even longer than that just out of admiration of the knife, is probably the most I'll do that. Other than that, the knives only flip out when I need some cutting done.

As far as this post, I was mainly asking in reference to linerlocks since that is my preference. I just don't like how framelocks feel since only one side is a scale.

If as you say, .07 is at best annoying, how does it feel to engage/disengage .095? I can deal with hard to close as long as it's doable and not dangerous to the point where I risk dropping the knife every time I disengage the bar. I have an iron grip from over a decade of strength training. Just curious. I doubt I'd ever want .095 inch thickness at the relief cut (should the lockbar have one that is). But a happy medium is what I'm trying to find.

What I would give to have a bunch of different thickness lockbars to see how they feel. haha. Now that would be an experiment.

 

[Darrel Ralph]

Hark,
I agree with STR that there is not a lot of need for change in LB set ups.
I know of ten of them that work just fine.
Making the relief thicker is a problem.
It becomes hard to close the lock, pushes the blade off center, tweaks the frame off center and a few other things.
This is up for much discussion and debate.
One system that I always was interested in was the one that Tony at Micro Tech came up with.
He used a hinge as the relief with a 17-4-ph lock on the lock of some of his otf and socom knives years ago. So if the hinge is as strong or stronger as the bar, you have a winner. That is one way you could possible achieve your quest.
Every knife maker worth their salt has a formula that has evolved over the years (if they have enough time in) and they know what works well and what does not work.
I think this boils down to trust in the maker More than speculating a air theory.
Lock bars are like a recipe. There are many ingredients that are up for speculation and many hours of design work that go into them.
A good maker has a method that is in stone and it works.

Finally you can beat this to death if you want.
It is like many things in life, everyone has an opinion. The nice thing is when people can talk it is nice when they realize that what they are saying should always be an opinion, not a statement, unless they can prove what they say technically and for certain is true and not their opinion. The best lock is the one that works and lasts for years of use. That is a statement.

So basically if you trust the knife maker you are working with, then that should be enough.
DDR

 

[STR]

I don't have that habit. Once or twice here and there when I'm bored over the course of a week or even longer than that just out of admiration of the knife, is probably the most I'll do that. Other than that, the knives only flip out when I need some cutting done.

As far as this post, I was mainly asking in reference to linerlocks since that is my preference. I just don't like how framelocks feel since only one side is a scale.

If as you say, .07 is at best annoying, how does it feel to engage/disengage .095? I can deal with hard to close as long as it's doable and not dangerous to the point where I risk dropping the knife every time I disengage the bar. I have an iron grip from over a decade of strength training. Just curious. I doubt I'd ever want .095 inch thickness at the relief cut (should the lockbar have one that is). But a happy medium is what I'm trying to find.

What I would give to have a bunch of different thickness lockbars to see how they feel. haha. Now that would be an experiment.

I have actually done that experiment with my own folder model which I now call the "He Man" and in my own experience .050 to .059 seems to be about the perfect place for the lock cut to me. Of course if I had just opened my eyes and paid more attention earlier I could have saved myself the work by simply examining the Sebenza closer. Chris does one of the better lock cuts in the industry in my opinion. I wish I liked the model more and could actually take to the shape of the blade and handle but I've owned three Sebbies and sold or traded all three great as they are for engineering, build tolerance and quality.

In a liner lock .070 works fine. A solid .070 liner and a .125 or thicker slab thinned down .070 are not the same animal and do not feel anywhere near the same to the thumb or the action of the blade. Something adds ummmph to the thicker slab models and I'm not sure how to explain it. Buck made the Buck Strider liner lock 880 and 881 models with .070 liners of titanium and they never gave anyone any problems at all. There were no lock cuts at all in those liners and none were needed.

The current He-Man model I've made in .0935 to .095 solid ti slab sides are a long term trial and error effort. The lock has to be long enough to allow good leverage so you can manipulate it, with the idea being that its easier to move a longer piece of metal than it is to bend and manipulate a short stout one and the spring tension has to be just so to allow it to work well. Even trying to do this I tell folks its not the kind of knife you'll want to sit around opening and closing for the fun of it. You'll develop carpal tunnel fast doing it lets put it that way! If you only pull it out when you need it they can be used and you'll come to appreciate it I think.

I've done them both ways and more have a slight lock cut done shallow than not but there are several out there now that are solid lock bar models. The owners don't seem to be complaining about the locks so I guess they work okay for them although I did have one sent back to have a lock cut put in it after he had it for a while. Apparently in his case anyway it was just too much spring tension fighting his thumb all the time. I can understand that and had no problem thinning it in back some to ease that pressure for him.

STR

 

[harkamus]

I love healthy discussion. This is what makes bladeforums so amazing. You can get views from users and makers alike. I wasn't aware of the other variables that could get tweaked by a thicker lock bar like the blade and frame being thrown off center.

That hinge mechanism lockbar sounds interesting. I wasn't aware that there was another maker that used a hinge beside Cold Steel.

So basically if you trust the knife maker you are working with, then that should be enough.
DDR

You know your stuff. Of that I have no doubts. Definitely looking forward to stopping by the booth at Blade this year. Maybe I should be the one buying you a drink. haha

there are several out there now that are solid lock bar models. The owners don't seem to be complaining about the locks so I guess they work okay for them

The one thing that I'd be worried about for a knife that has a thicker than .05 - .07 "area where the lockbar bends" (I put that in quotes since now we're talking about solid lockbars at that thickness or lockbars thicker that have that area thinned to be .05 - .07) is the ball detent wearing out prematurely.

EDIT: Speaking of ball detents, I am reminded of when I owned a ZT 0350. I think the lockbar was .08 or close to it but with a relief cut out. I took the knife apart to replace a broken a/o spring (and cut myself pretty bad but that's another story) and noticed the ball detent had cut a channel on the s30v blade. Kind of the opposite of what I was expecting. Guess the ball was harder than the s30v.