why is eveyone changing the cut out on the lock bar from the inside to the outside.

E

ericvar101

Joined
Feb 24, 2012
Messages
738
I have several Ti frame locks that are a few years old, the cut out on the lock bars are all on the inside. I noticed that on most of the newer TI frame locks have changed the cut out to the outside of the lock bar. It looks kind of silly to me, I guess it's supposed to make it stronger or something. Anyone know why this change?
 
When there is stress on the lock, the resulting force on the cutout area can be divided into two components: one that compresses the metal and one that tries to bend it.

There's a bend in the cutout area, and the smaller its angle, the bigger is the compressive force and the smaller the bending force. Making the cutout on the outside reduces that angle reducing the bending force which should make the lock a bit stronger.
 
First, I'm not sure "everyone" is doing that, but the theory is more or less as outlined in the post above. However, when you consider failure modes of framelocks, the chances that it makes even 0.0000001% of a difference is very optimistic. ;)
 
It might be aesthetic preference of the manufacturer. It could also be due to that specific design you are looking at. Not all frame locks are created equally, there are a lot of variables involved in figuring out what will work the best for that particular product. Chris Reeve (father of the integral lock) seems to have left it on the inside.
 
Outside of said technical purposes, I prefer them on the outside. I feel that is adds some aesthetics to some knives such as the southard. The triple groove design is much more appealing than a flat slab of Ti.
 
steff27 said:
When there is stress on the lock, the resulting force on the cutout area can be divided into two components: one that compresses the metal and one that tries to bend it.

There's a bend in the cutout area, and the smaller its angle, the bigger is the compressive force and the smaller the bending force. Making the cutout on the outside reduces that angle reducing the bending force which should make the lock a bit stronger.
Click to expand...

Well said. To put it another way for the OP: When force is applied to the engaged lock, compression forces are imparted upon the lock bar. Since the weakest part of the lock bar is the relief cutout, it makes sense to put more material in line with those compression forces. To make this happen, material needs to be as close to the center of the handles as possible without interfering with the blade when it is in the closed position.

NOW, there are several other things to consider, like the radius or angle (if flat) of the lock face on the blade. The steeper the angle/radius, the more force is applied in a lateral direction to the lock bar, potentially amplifying (or even decreasing) the bending forces upon the areas above the relief.
 
An outside cut out may transfer more bending force into compression force (ie. stronger) but doesn't it increase slipping of the lock?
 
Cypress said:
When force is applied to the engaged lock, compression forces are imparted upon the lock bar. Since the weakest part of the lock bar is the relief cutout, it makes sense to put more material with those compression forces. To make this happen, material needs to be as close to the center of the handles as possible without interfering with the blade when it is in the closed position.
Click to expand...

In engineering terms if the cutout is on the outside, there is less eccentricity on the material left at the cutout. A compression element with a lot of eccentricity also has a bigger lateral force component on it, and the photo that I saw of a failed lockbar showed it failed in sidesway buckling due to the bigger lateral force component. I think it would be a pretty extreme event for this to make any difference, and I don't know under what circumstances the one that I saw actually failed. Personally I like the cutout on the inside so you don't see it, especially on my ZT 0561.
 
bdmicarta said:
In engineering terms if the cutout is on the outside, there is less eccentricity on the material left at the cutout. A compression element with a lot of eccentricity also has a bigger lateral force component on it, and the photo that I saw of a failed lockbar showed it failed in sidesway buckling due to the bigger lateral force component. I think it would be a pretty extreme event for this to make any difference, and I don't know under what circumstances the one that I saw actually failed. Personally I like the cutout on the inside so you don't see it, especially on my ZT 0561.
Click to expand...

No, seriously. In engineering terms, if you put the cutout on the outside, you can bolt the lock side down after drilling a few of the key holes and then do ALL of the milling operations on one side. It's a really really good reason to do it that way.
 
Like most features/changes these days as others have mentioned, they are likely driven mostly by trying to make the product at a cheaper cost. Look at the current trend of Ti/G10 handle knives, I'd bet a lot of money/time is saved by not milling/assembling a second G10 scale on both sides of knife, when having an exposed lock bar has more negatives downsides. It's the whole reason companies are using the liner/frame lock design in the first place, it's easy and cheap compared to far superior lock designs. Unfortunately it's not easy to do right consistently and we see posts displaying that every day.
 
You must log in or register to reply here.
Back
Top