Lockback lockup trouble

[Ryan Minchew]

Howdy gentlemen. Ive been playing around with trying to make a lockback and Im having a heck of a time. I have the "How to Make Folding Knives" with Lake, Clay, Centofante and I also have "The Lockback Folding Knife From Design to completion".
Ive beem following the Ron Lake method the most. Ive got the knife and lockbar back and ive been attempting to mock up all day. Once i get it set up and acting as a knife, i can easily push down on the blade and make the blade close with no real effort. The only way i can stop this from happening is to put so much preload on the spring that you cannotnpress the lock bar to release the knife ive tried piano wire and the square wire the normal supply houses carry. I can get the lock bar and blade to stick together no issues like several examples in the two books show. At first i had a bronze bushing that did not spin in the blade with a 1/8" pivot. This left the back of the lock right even with the back of the 1/8" pivot. I knocked the bushing out and used a 3/16" pivot trying to move the back of the lock towards the center of the pivot. Either way when i assemble the knife I can easily override the lock. I am going to attatch some pictures to see if anyone sees anything wrong. Thanks in advance for any clues or help

 

[Ryan Minchew]

Here are some pictures.

 

[KenH]

Ryan - have you read this WIP? http://knifedogs.com/showthread.php?28969-Lockback-Folder-Tutorial&highlight=lockback

It shows the spring a bit longer than your spring - I'm hoping to learn enough on these threads to make a Lockback folder for 2014.

Ken

 

[Don Robinson]

Hi there, Ryan! Your spring is way too short. Everything else looks fine.

 

[KenH]

Ryan, on the WIP I referenced above, go to page #6 and see a GREAT WIP on just the part you're having trouble with.

http://knifedogs.com/showthread.php?28969-Lockback-Folder-Tutorial/page6&highlight=lockback

My goal for 2014 is to make a lockback folder!

Ken H>

 

[Frank Hunter]

In his lock bar, that feature appears to be a notch to retain a free-floating spring instead of a short spring itself. I've attempted it that way myself before going to an integral spring brought out from the back spacer.

As for the lock not staying locked, the notch looks OK - in my limited experience and without being able to first-hand see the knife, I'd assume it's play in the pivot allowing it to come unlocked. Huge spring pressure should cram the blade to the edge of the pivot hole and attain lockup - but again then you can't get it undone as mentioned.

 

[Ryan Minchew]

Thanks for advice guys. I also asked on blade forums because i like to collect as much information as possible.
Leads me to a couple of questions. As far as the spring being too short wouldnt changing the position of piece to hold compression on the spring and adjusting the preload of the spring solve this problem? I maybe wrong thinking this is the case. Or is it too short in relation to where it is by the pivot? Ive changed the position of where and how much preload there is and no change until it doesnt work at all.
I went back through the books and one example has a square lock cut in the blade with a slightly angled front lock lug. The others all have angles to varying degrees. I pulled out the few cheap productions i have and all but one has square locks cut with a slight angle on the front of the lock lug.
The more i look and play with it, makes me think i shouldnt have put the angle on the back of the lock notch in the blade. It looks like it has a good cam effect that can be overridden.
As far as play in the pivot this was my very first thought. When i had the bronze in i had very slight play, i knocked it out and used a 3/16 pivot i had to actually lap into the liners and blade by alot, eliminating blade play. It didnt change the problem any. All the advice is appreciated and thanks for the wip link. I can only get it to partially pull up on my phone, but wi get to a computer later. Thanks

 

[Frank Niro]

Mr. Robinson is very sharp on the folder particulars and has written WIPs that are marketed. As well he also lives in Texas that makes him special just for that he told me. Frank

 

[Don Robinson]

Well,Frank, I'm no more special than any other cowboy.

Ryan, all you need to do is make a longer leaf spring that bears against the back spacer on the end of the knife. Insert it into your existing lock bar cut.

 

[Ryan Minchew]

Mr. Robinson is very sharp on the folder particulars and has written WIPs that are marketed. As well he also lives in Texas that makes him special just for that he told me. Frank

Well,Frank, I'm no more special than any other cowboy.

Ryan, all you need to do is make a longer leaf spring that bears against the back spacer on the end of the knife. Insert it into your existing lock bar cut.

:thumbup::thumbup::thumbup:

 

[Ryan Minchew]

Im hesitant to post this for fear of upsetting the "things seem to be headed in the direction gods" but after messing with it and talking on the phone with Ron Lake, i believe it was an angle problem.
In the book it shows the blade as having a 6 to 8 degree angle on the back and 4 to 5 on the front. Mr. Lake said he has gone 5 to 6 on both with the lock lug being one or two degrees less. Also i misread or miscalculated the lock spot in relation to the pivot. He said manufacturers put the back of the lock lug right dead centerline of the pivot. He puts his back .010 or .020".
also reading the book the Centofante method uses a square slot cut in the blade. The lock lug itself has a slight angle on both front and back, but not opposite making a taper the angles run parallel to each other.
Ron Lake also told me I would have a solid lock up with very very very little spring pressure. Well using a conglomeration of all the info I received here, books, and Mr. Lake i "think" i have something that will work.
The lock bar in these pictures is heat treated, the new blade is not.
Square lock notch in blade, back of lock notch on or just behind centerline, and slight parallel angle lock lug. Even with no spring the knife locks up. No amount of downward or upward force moves the lock bar.
The above picture is just the lock notch cut out of blade steel. Wasnt going to profile the blade if the lock sucked lol.

The next picture i hope shows the angles on a new lock lug to a lock bar i havent made yet. I still need to grind the relief into the bottom of the blade the let the lock bar sit flush closed, i was just trying to get the lock working.

 

[KenH]

Well shucks Ryan - now I see that your spring wasn't all that short after all. I only saw the very short metal that I thought was your spring, that's why I was thinking your spring was too short. BUT, that wasn't your spring at all - just the holder for the spring. Good point on putting the back of the lock lug .020" back of the pivot point. That would give allow lock to be free just a bit easier than dead center.... I think anyway.

I'm sure learning a lot about lock backs!

Ken H>

 

[Ryan Minchew]

Well shucks Ryan - now I see that your spring wasn't all that short after all. I only saw the very short metal that I thought was your spring, that's why I was thinking your spring was too short. BUT, that wasn't your spring at all - just the holder for the spring. Good point on putting the back of the lock lug .020" back of the pivot point. That would give allow lock to be free just a bit easier than dead center.... I think anyway.

I'm sure learning a lot about lock backs!

Ken H>

Lol, i was confused a bit on the short spring, then realized what you were refering to. I made two integral springs for this blade and just did not like them i orginally madenone 5 or 6 years ago and it broke the first time i mocked the knife up. I decided to go with a seperate spring because i felt i had more adjustment options being my first lockback i saw this as a plus. I habe put piano wire flattened on that one end and used this flat stock and i cannot feel a difference in either material.

 

[Don Robinson]

Ryan, looks like you've matched the angles on the blade and bar lock notch so well that you have a mechanical lock. Use a slight angle on the blade notch at the rear to prevent this. The bar lock can remain square.

 

[KenH]

Sounds like Don has the right idea - with the sides on both blade and bar notch being very straight, that would provide the mechanical lock. Remember, the bar comes up in a "circle" with the center at bar pivot, so there MUST be an angle that at least matches that circle. Straight sides would require the lock bar to lift straight up. I'm sure everyone else realizes that, but it just now came clear to me the "why" of the angle in the blade notch.

Ken H>

 

[Ryan Minchew]

I drew a picture that shows the angles a bit exaggerated, but would this do the same? I put together a mock up before i did it this way and it seems to be working. When the lock bar pivots on its circle the points making contact pull away from the lock notch in the blade.
Will a mechancial lock cause issues? Sticky lock ect? Thanks again for the help and advice, trying to take this all in.