Lockback geometry what am i doing wrong

[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

 

[Rat Finkenstein]

I am not a knifemaker, but my lockbacks have vertical and not angled locking surfaces. the cutout in the tang is square.

 

[Bill DeShivs]

Get rid of the angle!

 

[Ryan Minchew]

All but one of my production lockbacks do as well. One is angled. The two books i have show 4 different examples by 4 different makers and 3 angle on one or both.

 

[12345678910]

I agree something in the lock bar angles


http://knifedogs.com/showthread.php?28969-Lockback-Folder-Tutorial

I read the book, don't remember all the details

IN this photo, on the left, it makes sense to me for there to be an angle to allow tapered fit wear adjustment

On the right side, angle on that side with blade down pressure will cam the lockbar out of that joint
90 on that side makes sense to me.


KR also did the eight degrees too

How are you cutting that notch?
by hand, or mill ?

Visually it looks like more than eight degrees on the right side
I'd try to do a right angle, maybe a degree off or so

 

[Ryan Minchew]

I used a mill. And I just looked Centofante used a square lock, Clay says slight angle on both faces, Ron Lake shows 4 to 5 degrees on the front and 6 to 8 degrees on the back. The other books calls for 8 to 9 degrees on the back and square up front.

 

[Ryan Minchew]

Im going to make another blade tomorrow with a square cutout. I would have to double check, but i think input a 7 degree angle on the back. I split the difference from the book. Thanks for the help and any any more ideas keep em coming.

 

[Ryan Minchew]

After reading through the books again and talking to other makers i "think" ive got this going my way
I ended up making a square lock notch in the blade. With the back of the lock notch about .010" behind centerline of the pivot. On the locklug itself i did an angle on both faces, but not angled to where it makes a tapered lug. They are running parallel to each other. This is the way Frank Centofante did it in the book. Even with very little to no spring pressure it locks up in the mocked up liners. Ive attatched a picture on how I cut the lock lug. The drawing is exaggerated in reality the angles are 2 to 3 degrees.