Up & Down Blade Play

[bhuber]

Does anyone have any tips/tricks to reduce some slight up and down blade play on a 1970 Case 6344?

[OLDE CUTLER]

Does anyone have any tips/tricks to reduce some slight up and down blade play on a 1970 Case 6344?

If you mean that the blade has some looseness in the direction of the arrows with the blade open, probably wear in the joint and is not readily fixable without a major effort.

[tallguy606]

I was wondering the same thing about a Schrade USA LB 7 folder that I have. With a thick steel blade, massive brass bolsters, and a heavy steel pivot pin in those bolsters, how could slight vertical play have developed? Which of these parts deformed a little? Assuming there was no play when the knife was new.

[Jeffinn]

I was wondering the same thing about a Schrade USA LB 7 folder that I have. With a thick steel blade, massive brass bolsters, and a heavy steel pivot pin in those bolsters, how could slight vertical play have developed? Which of these parts deformed a little? Assuming there was no play when the knife was new.

Could be a worn pivot pin or a worn pivot pin hole in the blade. I’m not sure how common that is or why it would occur.
Jeff

[bhuber]

Does anyone have any tips/tricks to reduce some slight up and down blade play on a 1970 Case 6344?

If you mean that the blade has some looseness in the direction of the arrows with the blade open, probably wear in the joint and is not readily fixable without a major effort.

IMG_2983.JPG

Yep, that is what I’m experiencing. Thanks for taking time to answer. It’s only slight and still a good knife for light cutting chores.

[glennbad]

I see up-down blade play in lock backs, not typically in slipjoints. As others mentioned, probably a work tang on the blade or pivot pin. Sometimes you also get that if the pin has been replaced, and is undersized for the hole.

[ea42]

Up and down play on a pocket knife is caused by wear on the back tang, or a combination of the back tang and spring. Normally there is a gap beneath the spring when the blade is fully opened. This keeps downward spring tension on the tang, forcing the blade back tightly against the end of the spring. If that gap is closed due to wear, the spring winds up resting on the flat, cancelling out the forward pressure against the tang. If the wear continues to the point in third illustration, you've got a wobbly blade:

This can also happen if the spring is too short, but in that case the blade will appear to be over-extended when open, kind of sticking up beyond where it seems it should have stopped. this is referred to as a broken back.

A loose lockback blade is usually the result of the lock lever not engaging tightly due to a poor fit.

Eric

[TripleF]

Up and down play on a pocket knife is caused by wear on the back tang, or a combination of the back tang and spring. Normally there is a gap beneath the spring when the blade is fully opened. This keeps downward spring tension on the tang, forcing the blade back tightly against the end of the spring. If that gap is closed due to wear, the spring winds up resting on the flat, cancelling out the forward pressure against the tang. If the wear continues to the point in third illustration, you've got a wobbly blade:

Knife tang wear.jpg

This can also happen if the spring is too short, but in that case the blade will appear to be over-extended when open, kind of sticking up beyond where it seems it should have stopped. this is referred to as a broken back.

A loose lockback blade is usually the result of the lock lever not engaging tightly due to a poor fit.

Eric

Awesome illustration and explanation Eric. Thanks!!!

[Dinadan]

Thank you, Eric, for a very informative post!

[ea42]

My pleasure guys, always glad when I can contribute something. Glad you can make sense of my rudimentary artwork!

Eric

[muskrat man]

I was wondering the same thing about a Schrade USA LB 7 folder that I have. With a thick steel blade, massive brass bolsters, and a heavy steel pivot pin in those bolsters, how could slight vertical play have developed? Which of these parts deformed a little? Assuming there was no play when the knife was new.

Big heavy knives are subject to abuses because people assume because a knife is heavy and well built it is indestructible, pins will bend/wear under excessive forces. I see it all the time with LB&, buck 110 and similar lockbacks. It is also possible that the steel in the mating surfaces has been worn or displaced from these forces/lack of lubrication over the years as well

[cudgee]

I have had this problem with 2 brand new purchases this year. Sent them back. But was annoyed, should not happen with brand new knives after two months of light use.

[orvet]

Excellent topic! I really appreciate the input and Eric's great drawing!

Some of the newer LB blades have a larger pivot hole drilled in them and they also use a bushing. If that bushing is worn significantly couldn't that also cause the up & down play in the blade?
What do you guys think?