Grip stability vs ergonomics + misc.

[JoHnYKwSt]

Greenjacket,

Once the blade is deep into this type of material, it becomes stuck. Its the getting the "dam" knife out that puts the pressure on the lock.

I realize this. But what are you cutting into that binds to the knife so much that when you pull it out, the force caused generates enough pressure to bend the liner?

If we only used a knife for making straight cuts; why have any thickness to a blade?

What do you mean by this? No one ever said we use knives for only straight cuts.

The gerber went flying and he bust his hand.

Can you explain this in more detail? It sounds like he was cutting the branch and when he got through the branch flew back. How does this cause the lock to break?

-Johnny

 

[Cliff Stamp]

John, I made some comments about strength as your argument against the examples I used was that the knife user would not be strong enough to exert enough force to break the lock and/or be able to maintain his grip on the handle. As for impacts vs loads, both will happen, the loads are usually much less dangerous as they are not as sudden and the blade is not likely to close on your hand once it fails.

For example in the cutting heavy material examples, once the blade binds, you don't pull it out, this is very difficult and fairly dangerous as the release is not going to be very controlled. I usually just press down very hard on the handle so as to loosen the blade. Some cutting requires a constant torquing around the piviot as you are working through the material. This is putting the same stress on the blade as if I viced the blade and repeatily pressed down and hauled up on the handle.

There are variations of course, on some brittle materials like wood I will first try to just twist the blade so as to break the wood sliver off. This would also put a lot of stress on a lock in a diffent plane though and I don't know in which one the various locks are stronger. If this fails then I will again do the torquing to loosen the hold on the blade. It would be nice if break tests were done for torques around various axis.

In terms of impacts, splitting wood is a example of how a lock can see a sudden impact. Jeff Randall and Chris J., have both described using folders for this. So have I, the Uluchet.

-Cliff

 

[JoHnYKwSt]

Cliff, I still do not understand how cutting rope or whittling wood and having the blade slip can in any way cause a lock to break. As for the blade binding, even if anyone was a complete idiot and pulled out the blade in the worst way, the force generated is not strong enough cause the lock to break. This may sound very general but I do not see how cutting anything and pulling out a binded blade can cause the lock to break.

 

[Cliff Stamp]

John :

pulled out the blade in the worst way, the force generated is not strong enough cause the lock to break.

Neither I nor the other individuals who gave examples were pulling along that axis. The listed descriptions were of the user pushing down or pulling up on the handle and thus creating a torque on the piviot in the same manner as if the blade was viced and you pressed down / pulled up on the handle.


-Cliff

 

[JoHnYKwSt]

Neither I nor the other individuals who gave examples were pulling along that axis.

You can pull along any axis you like, it makes no difference regarding my point.

The listed descriptions were of the user pushing down or pulling up on the handle and thus creating a torque on the piviot in the same manner as if the blade was viced and you pressed down / pulled up on the handle.

What is your point?

OK Cliff, I'm going to put an end to this discussion since it seems you will not. The majority of this thread has been nonsense.

-Johnny

 

[Cliff Stamp]

John it makes a tremendous difference how the the force in being applied for two reasons. First of the all the strength of the lock is vastly different depending in which direction you exert the force on the lock. Second, the necessary grip strength to support the force varies hugely. In more detail on the second factor :

Assuming a 200 lbs thrust, you can easily support a downward push on the handle because the grip will rest in the center of your palm and all you have to do is stop it from twisting, which will not be much effort assuming you can press in a fairly straight line.

However pulling straight up on the handle (or to the side) exerts the full force of the pull on your fingers. On such a tight grip as would be used (because knife handles are thin), your grip will probably fail long before your ability to pull will, unless you have trained one and not the other.

And fincally, if you are pulling out on the blade you must exert enough force on the handles to generate the necessary friction to stop the blade from slipping out of your hand. Depending on the frictional coefficent and the ergonomics, this could be twice as much force or more than the pull - so you are in the range of a 400 lbs compression. There is currently only one person capable of that level of compression with his grip on the planet.

As for generating these forces in the first place, awhile ago I did some measurements and it required over 200 lbs to get some blades to penetrate into 1/2" cord, at at 300 lbs they had still failed to go through the material. They were all freshly sharpened, but some of the popular tactical knives have very thick and obtuse edges and require extreme amounts of force to push cut through things.

This of course is why the strength of the user is a factor, if you can't push or pull hard enough you are not going to obviously generate these forces when cutting. If you can then you will be able to whittle very deeply, pull blades through very thick cord, work them through very resistant plastics etc. .

By the way, for reference, in comparision, a well ground blade from Boye, Wilson , Schott etc., will make the push cut through the cord at around 30 lbs.

-Cliff

[This message has been edited by Cliff Stamp (edited 09-22-2000).]