"Drop-shuttyness" and how to optimize with bearings

Just use them.

 

Probably the person(s) on the vids had the pivot loose so they'd fall free at the expense of positive lock up.

 

Most moderately priced knives are gonna take quite a bit of open /close before they are broke in. Until then they are gonna be a bit stiff. As the man said, just use it.

 

I bought my first Chinese bearing knife recently, a Kizer.
I thought it would have that drop shut action that many talk about so I was a little surprised when, in fact, it didn’t come close to that at all.
In fact, as I opened and closed the blade it was so rough I could almost imagine that I was able to count each individual bearing as it clunked along its glide path.

I disassembled the knife, cleaned it, it wasn’t really dirty as it was new,oiled, reassembled and had the same clunky action.

So I disassembled it again.
This time polished the bearing races and the detent track on the blade using Mothers Mag Polish.
What a difference, no more clunky action, silky smooth and ‘drop shuttyness’ with proper blade tension.
I suppose I just sped up the brake-in process that others have mentioned above.

 

The lock bar and detent are going to have more of an effect on the action of a knife. Take any bearing knife (or well made PB washer knife for that matter) and hold the lock bar off the blade. It will be completely free swinging. Now let go of the lock bar and the detent acts as a "brake" on the blade. Polishing the detent track can help, but I'd guess that the reason YOUR knife wasn't like the one's you've seen is because your knife's lockbar was bent more from the factory. Causing the detent to "brake" the blade more.

 

Well ideally you'd want the lock bar sprung at least to the other scale, so that as the lock wears, it adjusts, and you get the full life out of the lock. That doesn't exactly take into account the action of the knife though. I've bent plenty of lock bars and there is a risk in doing it, if you bend it backwards enough the the knife might not lock up anymore. Or it might lock up but slip if there is little tension and/or the geometry of the interface is off. Trick is to go very slowly, a little at a time, and reassemble and check how it all fits often in the process. Since you're talking about a ZT you'll need to remove the lock insert to over extend the bar.

In my mind there are 2 routes you can take concerning how sprung your lock bar is:

1. Bend the lock bar fully to the other scale so that your knife is self adjusting for the life of knife. You'll have to get over the action not being "drop shutty" but you can rest easy knowing it will lock up the same forever.

2. Bend the lock bar so it is just passed or just to the point of locking up. This will give you the best possible action with the given engagement point but you run the risk of the knife not locking up properly, possible lock slip if the geometries are not good, and the real possibility of developing lock rock as the knife wears and breaks in. If it gets to that point you'd have to disassemble and add a little more bend for it to lock up properly, sacrificing opening action every time you have to add more bend. The positive being you may have a drop shutty knife now, again dependent on the engagement point.

The absolute most drop shutty action is going to come from knives that have a very early lock engagement coupled with a very weakly sprung lock bar. Early engagement allows the minimum of lock bend, minimum lock bend allows the most free action aka drop shuttiness.

Keep in mind that lock bar tension also plays into flipping action. It's not solely responsible but factors with how far the detent ball is pressed into the lock bar, the depth and size of the detent hole in the blade, and the general interface of the detent ball and hole (different makers set up their detent ball/hole interface differently). Removing/adding tension to the lockbar will undoubtedly change the flipping action of the knife, not necessarily in a bad way (personal preference) but it will change it