The Mechanics behind Lock Rock Explained.... (Pics Included)

JR88FAN

JR88FAN

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May 5, 2013
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First of all, I want to apologize if this thread is in the wrong sub-forum.
I took a long look at my options, and 'maintenance' was as close as I could find...

The purpose of this thread is to quickly explain and show the issues behind lock rock for those that may be interested in seeing what contributes to this problem.

If I miss anything, please fill the gaps, it would be much appreciated.

I am using Two Strider SMF's for my example pictures. (all makes of frame locks can and have developed this issue if the geometry is not correct)
The SMF is hands down my personal favourite folder, however, it's no secret that earlier generations had issues with lock rock. Let's see why:
 
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On the left is a newer SMF using a much better tang cut angle.
The SMF on the right is Striders old tang geometry.
If you look closely, not only is the angle much more steep on the old geometry, but the actual right side of the tang has a very abrupt upwards cut:

 
As the titanium lock bar wears against the metal tang of the blade, it will start to slowly move closer to the show side.
This is normal wear. However, depending on many factors, including tang radius, lock bar cut out/tension, carbodization, this may happen very gradually to Almost no noticeable movement of the lock bar over many years of use.

Unfortunately, the lock bar tension on this SMF coupled with the overall geometry of the bar itself, and radius of the tang (especially that very steep angle) are the perfect combination for developing lock rock relatively quickly.

Notice lock bar contact with the blade tang: New Geometry:



Old geometry: (only the very top portion of the lock bar is touching the tang....

 
When such a small portion of the lock face is making contact with a blade tang that has an extremely steep radius, what you end up with is much faster wear because all of the pressure is on that small top portion of the lock bar.



Lock rock occurs when that small portion of the lock face meets the the extremely steep angle of the tang.
The titanium lock face is trying to stick to what is essentially a slope (radius of the blade tang in the old version) Any negative pressure on the spine of the blade will make the lock face slip off the tang.
The small contact point and the highly sloped radius ensure the knife will have up and down play (lock rock)

The lock face will slide down the slope of the blade tang with any negative pressure applied to the blade spine, and stop as it hits the less sloped part. As the pressure is removed it will try to slide back up the overly sloped part.

To simplify, if you apply negative and then positive pressure to the blade, you will see the lock face slip back and forth, and the blade will have up and down play, hence the term lock rock.

On a knife with a tang this steep, bending the lock bar farther in will not solve the problem. The angle is so steep, there is no way the lock face and the tang can form a solid locking surface.
The only real option here is larger stop pins, putting pressure on the lock bar, to not allow the lock bar to travel to where the angle of the tang is really steep.
 
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If I made any errors, or left something out, please correct me.

I hope that by posting this, it may answer some questions for anyone curious about lock rock and why it develops.

Thank you.
 
Yea.....what he said. ....good read 88fan.....SMF is my fav also. Awesome pics by the way man. I compared mine and I have the new lock geo. Locks up like a bank vault.
 
Hey bud thanks so much for the posts and pics!! I can tell you put a lot of work into this! Would you say there is a difference between lock slip and lock rock or would you say they are one in the same?
 
Sounds right to me.

The old tang was ground with a 1" wheel while the new one is done with a larger wheel. At least that's what Strider told me when I told them about my SnG. Seems like taking a file to the tang would help, but only if you catch it soon enough.
 
Great write up Alex. Definitely put some Time into this. Makes perfect sense after seeing both side by side here.
 
razor-edge-knives said:
Hey bud thanks so much for the posts and pics!! I can tell you put a lot of work into this! Would you say there is a difference between lock slip and lock rock or would you say they are one in the same?
Click to expand...

Hey Josh!

From my experience, yes and no.

The condition of lock rock does involve the lock face slipping back and forth from the crazy radius corner to the more 'flat' side, hence the word 'rock' however 'lock slip' can mean many things;

To me, first it means a very early lock-up coupled with a bad geometry/cut out so the lock has a tendency to fail.
That issue can usually be fixed by bending the lock bar.

Lock slip can also mean that the lock slips all the way across the tang and gets stuck.
That would also be a geometry/tension issue, or it can be caused by excessive lubrication on either the tang or lock face.
I saw this issue with an XM, it was a result of both.
 
Gizler00 said:
Great write up Alex. Definitely put some Time into this. Makes perfect sense after seeing both side by side here.
Click to expand...

Thanks Mark, appreciate that...

I wish I could take better pictures, the older version Strider tang looked like a wave!!
It was never going to work, and it's not hard to see that coupled with the bad lock face contact, lock rock was inevitable.
But hey, they addressed the issue.
 
Good observation!!

If more tension on the lock bar or frame adjustment does not solve the problem, then either a larger stop pin or a new frame side are the options.

Although you are using Striders as examples let's be clear that this is a potential issue for any frame/liner lock knife.
 
Thanks guys.

I think there are a lot of mis-conceptions about lock rock, and I was hoping to clear some of that up.
Also, when you buy a frame lock, these photo's should really help you understand the geometry of what you have and the potential issues down the road, based on how it was put together.

This is NOT anti-Strider.
I will say this again, I never go anywhere without an SMF in my pocket, and in for me, Strider makes the best tool.

This geometry issue is not exclusive to Strider, and has been seen on everything from productions to customs....
 
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