How do you deal with nailbreakers?

[kirk13]

There's always one. A pocket knife with a blade or tool that just won't open easily;that won't open even if you tear out your thumb nail trying. What do you do? What's the cure?

[dks]

Apart from washing, lubricating etc. Leaving the blade partly open, at around 90° stresses the spring and weakens it. Check daily - worked well with a few RRs

[AimlessWanderer]

1) Identify the cause
Four potential causes for a tool being difficult to get out are debris, friction, overpeening (or overly tight pivot screws) and strength of backspring.

2) Clean and oil the tool thoroughly. This will help eliminate any contributing factors from the first two causes, and it will aid visibility for identifying the other two.

3) If the tool has adjustable pivots, slacken them off temprarily ubtil there is slight side to side play. If this helps there may be some size discrepancy between the thickness of the backspring and the thickness of the tang, which means that whilst the tang of the knife is being supported properly, the backspring is being "clamped". If possible, dismantle the knife, and sand down the thickness of the backspring to slightly less than the thickness of the tang. Reassemble and try again.

4) If all else fails there is likely excessive strength or tension in the backspring. This can really only be addressed if the knife is dismantled, and even then must be done carefully to avoid inducing new problems.

The only real way to safely reduce the strength of the spring itself, is remove some of the thickness of the backspring, so that a thinner section is being flexed. Care must be taken to avoid weakening areas around support or pivot pins, avoid stress raisers at abrupt changes in section (sharp corners - all thickness transitions should be smooth and "sweeping").

If the knife cannot be dismantled for any reason, but the backspring is flush with the back of the knife, it may be possible to slightly thin the backspring by linishing the entire back of the closed knife. This should be done slowly and cautiously, noting where and pins (including hidden pins) may be.

Failing that you can try and sprain the spring by leaving it open at it's maximum point of tension for a while. This again may shorten the life of the spring. Once you have taken material to it's yield point and deformation occurs, the material has been irrevocably damaged. It may continue to function as a spring for many many more cycles (though less than it would previously), or it could fail much sooner. Chances are that a spring failing this way would noticably get more and more weak before it finally breaks, so at least you'll get some warning.

The only other ways to overcome this without adapting the backspring, is to rehouse it in new liners, with the backspring pivot in a fractionally lower position, and/or modify the tang of the blade, so the spring is under less tension and/or doesn't need to flex as far when the tool opens and closes.

There is potentially another cause, and that is an incorrectly hardened backspring. If the spring wasn't tempered back enough at the manufacturing stage, the steel may be too hard and too strong. This not only makes it a nail breaker, but means it will likely develop stress cracks and fatigue sooner. You're average bloke in the street doesn't have the facility to test for or correct this though, and if this is assumed to be the case and the metal is tempered back further, it could lose some of it's spring and over time will become deformed and the tools will not be held secure in the open positions. The only viable actions are to return the knife if bought new, or simply to blame Kirky, and carry a different knife instead

[AimlessWanderer]

Oh, I forgot the curse of the galled pivot. 

If a pivot pin/screw has galled, it won't matter what other work you do to the knife as effectively part of the pivot is the same size (or even slightly bigger) than the hole that's running on it. Only way to identify it for sure, and indeed to fix it, is to replace the pivot

[AimlessWanderer]

Well that killed that conversation. 

Just call me Al the thread killer 

 

 

[Toolslinger]

There's little to add to what you've already described Al. Very detailed and informative.

[PTRSAK]

The only problem with reducing the strength of the backspring is that it reduces the force with which the blade is held open, increasing the risk of a slipjoint blade closing on your fingers if you do something dumb like try a piercing cut (and who hasn't? I have the scar to show how dumb I am).

There is another way of reducing the force required to start opening the blade but it is rather fiddly and on some knives will be hard or even impossible to do without dismantling the knife.

It involves reshaping the side of the tang that sits against the backspring when the knife is closed.
This will be on the edge side of the blade when it is open but the area you want to get at will probably be between the liners. As I said... fiddly.

Removing material from this side only of the tang will reduce closing force, but will leave the snap holding the blade open at full strength.

How much material you need to remove and from where depends on how the tang contacts the backspring. If it is a flat contact you can bevel or radius the heel end of the tang which will lessen the force required to start the blade opening due to increased leverage.
To do the same with a concave tang closing surface is a little harder because removing material from only the heel can effect the closed position of the blade. You don't want your knife having the blade sitting with the tip exposed.
In this case you need to remove material from the blade end of the tang also.

This is all MUCH easier if you can do it with the knife apart and it is surprising how much a tiny amount of material removal can alter snap strength or blade angle.
GO SLOW AND CHECK OFTEN.!!!

[cbl51]

I just get rid of it.

I learned a long time ago, that they never get any better, and to just move on. This is why I only buy knives from a store where I can examine it. I don't buy on internet or mail order. Besides, the mom and pop brick and mortar stores need to be supported. In the end, it's worth it.

I'll never own a knife that I can't open with cold and/or wet hands.

[firiki]

Well that killed that conversation. 

Just call me Al the thread killer 

 

 

Wrong thread... See here: http://forum.multitool.org/index.php/topic,56735.0.html 

[firiki]

Loads of great info in this thread

Personally, I tend to use cbl51's approach. Especially this:

I'll never own a knife that I can't open with cold and/or wet hands.

[rebel]

There's always one. A pocket knife with a blade or tool that just won't open easily;that won't open even if you tear out your thumb nail trying. What do you do? What's the cure?

At first I thought you meant women. Anyway, my original Leatherman has that tendency. I just try to remember it and be a little careful.

[PTRSAK]

I just get rid of it.

I learned a long time ago, that they never get any better, and to just move on. This is why I only buy knives from a store where I can examine it. I don't buy on internet or mail order. Besides, the mom and pop brick and mortar stores need to be supported. In the end, it's worth it.

I'll never own a knife that I can't open with cold and/or wet hands.

That's fine if you are dealing with a new knife.

But many people here (and I know Kirky is one) like to rotate some vintage stuff through their EDC.
Personally I like to occasionally throw a m1908 pattern SAK in my pocket for the day. Usually it's a Wengerinox that's seventysome years old and it was a real nailbreaker (typical for a m1908) before a little tuning. Now it's pleasing to use and look at.