How strong/secure is the ball-bearing that holds framelocks closed?

peacefuljeffrey

peacefuljeffrey

Joined
Feb 24, 2001
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Well, the question in the thread subject says it all, except another question: How do they construct those things, i.e. how do they get a tiny ball into a hole, and in such a way that it does not come out? Oh, and another question: if the ball were to fail/come out/etc., would that mean the blade would just hang loose and free and the knife would be somewhat uncarryable?

If that last were possible and true, it would be one strong argument for lockbacks and axis locks.

Sometimes I'm able to put faith in things like springs, and "iffy" designs that seem to have inherent weaknesses -- particularly if the failure of only *one* aspect of a design would render the entire item unserviceable.

Other times, I want to stick with the least-possible-failure-prone designs, and that would have to be lockbacks (from the standpoint that their springs are both thicker than axis-lock omega springs, and tougher, and that they don't depend on some tiny fragile thing to remain held closed when not in use).

Different takes/opinions are invited.

---Jeffrey
 
How strong or secure the ball bearing is for a liner based lock? They varies. My Spyderco Salsa (compression lock, something quite similar to a liner lock) has a ball detent that holds the blade close very well. In fact, you can feel that it does hold the blade tight.
As to whether the knife would be uncarryable if the ball detent fails, I think a tip down knife in that situation won't be seriously affected unless something on the spine of the blade that tends to catch on things when you reach in your pocket. Tip up knives would be kinda troublesome unless you carry it such that the spine is right up to the seam of the pocket.
 
A few factors are involved. How deep is the detent hole drilled in the blade, how deeply set is the detent ball, how heavy is the lock and how well aligned is the detent ball with the detent hole. Done properly, this system works well. Most makers have this down with no real issues. I haven't had any problems with factory knives either. Of coure, that is just my experience.

The detent ball is press into the lock. The hole is slightly undersize to the diameter of the detent ball. Then the detent ball is pressed into that hole. If the hole is the correct size and the ball pressed into the correct depth, it won't be coming out with any ease.
 
I have found that the security of those ball detents can vary widely from manufacturer to manufactorer. In general frame locks seem to have exceptionally stiff ball detents. The Camillus EDC and my Greco Falcon are very secure, in the case of the EDC perhaps even too much so.

Some liner locks are similarly secure, while others are very loose.

In most cases the ball appears to be a simple friction fit inside a hole drilled through the liner (or frame). As long as the dimensions are correct this should provide a very reliable assembly. I have never personally seen a ball detent fall out or otherwise fail, and I have not heard any reports of this happening. If it does occur it is certainly a rare event.

I have seen some liner locks which have the detent simply stamped onto the surface of the liner, so the entire thing is composed of one piece. These do not appear to be as secure, and are subject to more wear than a true ball bearing which can be hardened to a greater degree than the liner material. Of course it is impossible for a stamped surface to fall out, so this could be seen as an advantage over assembled designs.

It is easy enough to see how secure a knife would be without the ball detent. Simply open the blade until the ball detent is bypassed, and there you have it. Running a couple quick tests on a Greco Falcon and a BM 690 it appears that there is a satisfactory level of friction to keep the blade closed even without the ball detent, although it is significantly less secure.
 
Thank you for the responses.

Based on the responses, for the most part, I think I did not make my question clear enough. I specifically was wondering about the security of the ball that is placed into the leaf spring of a liner lock or the inset spring of the scale of a frame lock. One poster said that the ball is pressed into a hole that is slightly smaller diameter than the ball, so the ball is held tight. I don't see how this is possible. I am picturing a semi-circular depression in the spring, and a ball pressed into that. Unless the aperture of the hole is less than the diameter of the empty space inside the metal, wouldn't the ball just fall out?

I understand that the security of how well the ball-bearing detent holds the blade closed is dependent on several factors, such as the depth of the depression in the blade tang and the spring tension of the lock itself.

Has anyone had the experience of the ball bearing falling out of the lock spring?

---Jeffrey
 
Originally posted by peacefuljeffrey
I am picturing a semi-circular depression in the spring, and a ball pressed into that. Unless the aperture of the hole is less than the diameter of the empty space inside the metal, wouldn't the ball just fall out?
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I believe that the manufacturers (the good ones, anyway) use a true drilled hole rather than a semi-circular depression. On all of the liner/frame locks that I have available right now the hole clearly goes all the way through the liner.

Think of if this way. If you took a golf ball and smashed it into a piece of pipe that was just slightly smaller that the outer diameter of the golf ball, it would likely never come out. This is effectively the same thing that is happening when the knife manufacturer inserts the ball bearing into the liner.
 
Having owned and used hundreds of knives I have never had one fall out. Not only is the ball press fit into the hole, many makers peen around the hole to hold it tighter.

I know Mike Obenauf had a batch of balls that were not heat treated properly and had to replace a few.

The detent ball that Mission uses on their MPF is made from UMHW which is a slippery plastic material, I felt this was a pretty cheesy design but they were keeping with the totally non-metaillic theme of the knife. Mine wore flat pretty quick.

Chris Reeve has a cool design where they use a ceramic ball and then I believe they weld a plate in over top of the ball to prevent it from falling out. If you look at the detent ball on a Sebenza you will see that the material around the ball is a different color than the lock bar itself, it's pretty impressive however they do it. Maybe someone who has talked to Chris about this can chime in, as I have not.
 
I've had ball detents fail. The ball in my mini AFCK wore off quickly and I a can see on some and sense on others the wear on other frame and liner detents I own. It's not a particularly durable system in the long run, IMHO.

BM replaced the whole liner on that AFCK, and not just the ball.

Phil
 
I will restate what I posted before. If they maker/manufacturer does this properly. correct alignment, correct depth of detent hole and detent ball, correct lock pressure this system works well.

The hole used to set the detent ball in is in fact drilled into the liner or frame lock. Some makers drill completely through the material others drill just far enough in to permit the detent ball to be seated properly. The diameter I was referring to was across the hole used to seat the ball in, not the depth of the hole. After rereading my post, it is a little fuzzy. Sorry.

I have seen detent balls wear to the point they no longer will engage the detent hole in the blade. That comes from using a ball that wasn't properly hardened. Since these are basically small ball bearings, they are purchased in massive quatinties from outside manufacturers. There will occasionally be problems like this.
 
If they maker/manufacturer does this properly. correct alignment, correct depth of detent hole and detent ball, correct lock pressure this system works well.
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There are plenty of variables and wear that can make this vary widely knife to knife and over time from the same maker. As both Dirk's "well" and my poorer statement are subjective, it really depends on what issues are important to you in a knife.

Do a search, there are many examples of the ball detent failing on tip up knives with this system while simply carried in a pocket. For me, it's too easy to defeat with the failure mode being unacceptable for my purposes.

The search isn't working for me right now, but there was a post a while back where a guy was playing with his daughter and she got stabbed shallowly because his knife opened in his pocket. As I recall, it was a liner or frame lock.

Phil
 
If the detent ball ever came out, the blade certainly shouldn't "just hang loose and free." Losing the ball wouldn't disable the "springiness" of the liner/ frame bar, which would then press directly against the closed ricasso. The ball functions to keep the bar from directly pressing against the blade itself, after all, and multiplies the spring resistance by concentrating it into a very small contact surface. While the bar alone wouldn't be nearly as secure as the detent ball, it should offer some resistance.

I would imagine that failure here would result from gradual wear, as some have noted above, rather than from having a ball immediately fall out. The former problem is addressed by good makers by using bearings much harder than the blades they secure; the Sebenza solves this by using a ceramic ball, also noted above. The latter problem would be exceedingly rare, as the ball is nearly always in contact with the blade surface, and the applied pressure works to keep the bearing in place. A closed blade that opens inadvertently will far more likely be caused by other factors, e.g., insufficient spring tension, dirt/ lint obstructing the area, etc.

To repeat the obvious, a folding knife is, by nature, a compromise. Of the various components that go into a good frame or liner lock, the likelihood of the bearing coming out would be one of the very last points of failure -- and less serious than failures on the locking end of the equation.

As for the "least possible failure" design ... Well, that's why God made fixed blades. :)

Glen
 
Originally posted by storyville
As for the "least possible failure" design ... Well, that's why God made fixed blades. :)

Glen
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And Bali-Song's :p :p :p
 
Originally posted by cpirtle


Chris Reeve has a cool design where they use a ceramic ball and then I believe they weld a plate in over top of the ball to prevent it from falling out. If you look at the detent ball on a Sebenza you will see that the material around the ball is a different color than the lock bar itself, it's pretty impressive however they do it. Maybe someone who has talked to Chris about this can chime in, as I have not.
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I know what youre talking about, that triangular area around the ball thats slightly colored, i dont think its a seperate plate though, i think its the area that they harden with heat to make the lock face wear more slowly, which is why it has that typical rainbow color that hardened Ti gets.
 
phatch is right. It comes down to personal experience. You gotta go with what works for you. However, if this were a truly bad design and really prone to problems, no one would use it. I need to amend my previous statement. I said I never had any problems. I forgot, I had a couple of issues with liner locks opening in my pocket. They were tip up knives and I got a nice little slice on my finger from that. That's why I now primarily carry tip down. That, is another topic and one that will be argued until the end of time. :)

Also as pointed out, a folder is a compromise for a fixed blade. As you increase the complexity of something, you increase the possibility of failure.
 
I'm told the ball is hardened 440C, and sometimes the stop pin is also hardened 440C. I know of a maker who only uses Superglue to hold the ball in place and he pretty much makes his folders impossible to dismantle. I don't think its a good idea, but thats a sure way to ensure the ball doesn't fall out !! I have seen the really cheap Taiwanese made folders where the "ball" is actually stamped from the opposite side of the liner, creating a hump that functions like a ball. Of course this is on the thin type liners. Jason.
 
I purschased a folder at a show from a well known maker who had an excellent reputation.By the time I got home the ball bearing fell out.I sent it back to the maker.After he apologized and paid for the mailing I got it back in a few days.That was about 3 yrs.ago and its working great.One of the reasons I bought the liner lock was the ball bearing was a little higher out than other ones and made a loud click when the blade passed it.This also kept the bladefrom opening accidently.
 
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