lockback folder design question...

G

gixxer

Joined
Sep 21, 2006
Messages
1,472
So I have been hitting the autocad pretty hard the past few days, got an inkling to build a lockback from scratch with no plans from another source. My question is this. How deep does the actual hook (lock, whatever you wanna call it) on the lockbar have to be in the blade for a safe and positive lock? 1/8"? 3/16"? This would be for light duty, steak cutting, whatever, and the blade itself is about 3 1/2" from tip to pivot. Gonna use .093 stock for the blade.

Interesting sidenote. Although learning how to do CAD can be irritating and time consuming, it helps cut down on trimming and fitting time (I would hope) by being able to rotate parts to see if you have clearance and such.
 
I end up with about 1/8". A deep lock is nice because you get a tight feel and have room to make adjustments before the key bottoms out. BUT you must lift the key over the edge of the lock buy pressing on the back. if you center the pivot pin then the back must go down 1/8, if off center then more or less depending on if you move the pivot forward or back.

the bigger issue is the spring, you need a really tough spring or the knife lacks snap on the open and close.

I make a plastic model after drawing to work bugs out, you should be able to get alot of the design worked out on the CADD.
 
I always made my own few lockbacks so they sunk in to what I felt was adequate for the size and spring design allowances in the folder. If they sink too deep sometimes the spring bottomed out and it was difficult to close. Most always I left the rocker arm notch so it would not bottom out in the blade notch. This allowed some space so lint could not affect the lock right away if it got in there, which in my mind was a plus to allow for some space to prevent accident. It would only be affected once it would be extreme levels of build up which would probably be noticed faster than a tiny bit. Thats what I felt anyway, at least in my own mind.

The old saying that we used in my old business was to pick someone you feel is doing it right and emulate them doing all the same things they do and basically I work on so many folders for folks that I had a pretty good idea of which makers and companies were doing some exemplry work and which were so so. I picked the ones I felt were the best and basically copied what they did.

You see various ideas of what is best in all the makes and from varioius makers. For me my main focus was the heavy duty and medium duty users from the manufacturers. I've noted the ones built in Japan seem to always seat all the way bottoming out and fitting together precisely filling the lock notch in the blade nearly exactly leaving little room for any build up and as a result these and some like the Fallkniven U2 and others all have locks that are affected nearly immediately with the slightest bit of lint build up.

I don't just say this lightly. I've seen it off and on. I can't count on both hands how many times folks have sent me their lockback knives out of the blue without first talking to me on the phone or in email about their knife that had a lock that worked great and then suddenly stopped working right. They send it off without noticing that its just lint in the lock notch and I get the knife and its a two second fix with a dental explorer. These that I speak of are most always a high quality Japanese knife of that 'precise fitting mold' or one of the others made the same way. In contrast, I have never been sent a Spyderco for this or a Buck lockback which both have some space under the lock cut so to me the ones that didn't bottom out built like these seemed to be better although, I'm not looking to get into it with those who have opinions that differ but thats just my opinion based on what I have seen.

To me this is probably as important as how deep and the angle of the contact so its almost wedged in there instead of squared off when it connects. I always look at the Spyderco Manix and Mini Manix as what I think of as 'perfect lockups' personally. But thats just me.

STR

Good lock.jpg
 
Yup. figured out how deep to make the finger cutout on top by rotating the lock till it cleared the blade, then drew the cutout.
I plan on making a couple different spring grooves to get the angle right for the right amount of tension without having to bend the spring at all.

Right now what I have drawn has the lock a hair under 3/16 give or take.
 
I think 3/32 or so is good because the deeper your lockup the deeper you must press lockback to unlock. This can become difficult with a strong spring. The depth of lock is reliant a bit upon strength of spring. Position of pivot pin on lock also affects depth of notch. The closer the notch is to the pin,the deeper you must depress to unlock.
 
STR, awesome post for sure. I was contemplating the wedge also while in the deer stand last earlier this week. In my uneducated opinion I thought that if enough pressure was placed on the spine, then the lock would slip. Thanks for posting the pic for a reference. Without really looking at the actual lockup you would be led to think that 100% contact was key to a positive and safe lockup. Good point on the lint factor.
 
gixxer said:
STR, awesome post for sure. I was contemplating the wedge also while in the deer stand last earlier this week. In my uneducated opinion I thought that if enough pressure was placed on the spine, then the lock would slip. Thanks for posting the pic for a reference. Without really looking at the actual lockup you would be led to think that 100% contact was key to a positive and safe lockup. Good point on the lint factor.
Click to expand...

Glad you feel it was helpful. I'm sure there are folks that feel precise fit is best. Truth be told its obvious that both designs work but it just seemed to me the more precise fitting lockback rocker bars were more prone to immediate safety issues if you got something in the lock notch. As a result it appeared they needed more frequent care and maintenance and as most know to be fact, most end line users do not have real maintenance of their folding knives in their vocabulary. I think thats why most end line users (other than the knife nuts like here on the forums I mean) run around with knives with only vaque semblances of a cutting edge and consider it to be just fine. Based on my experience these types will sooner complain about a spot of rust on the blade than any edge keeping problems although there are some that will dig out first base with their blade and then write the makers with a complaint about what a crappy edge keeper the blade is. Go figure.

Anyway, the CAD should help a bunch. I am very illiterate with such things personally. Mine are still done with trial and error and card paper when I make one. Old dogs. You know the saying. ;)

Good luck with your project.

STR
 
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