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Thread: Strength of liner compression lock vs frame compression lock

  1. #1
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    Strength of liner compression lock vs frame compression lock


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    The Salsa would be a good example... How much stronger is the Ti salsa than the normal Salsa?

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    I'm not sure it is. This is probably something that could actually be calculated. Assuming the primary failure mode is compression of the tab, rather than failure of the frame/liner or the stop pin, you'd compare the crush (I think the steel geeks call it 'yield'?) figure for the Ti to the steel, taking into account depth and width. I wouldn't be surprised if the steel was stronger, even though it is thinner but that is a pure guess at best.

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    Would a frame style compression lock done in fullsteel be best?

    Im thinking about the coming Szabo folder. Im considering sending it to Reese or Nathan for a Ti locking side mod.

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  4. #4
    I think it really comes down to the shear strength of the stop pin. At some point those screws will crack through the liner and the lock will fail. With this in mind, i dont see liner or frame making any difference

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    Then further reinforced stop pin is in order? I wish Demko approached spyderco first.

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    Quote Originally Posted by Charlie Mike View Post
    Then further reinforced stop pin is in order? I wish Demko approached spyderco first.
    If you've ever looked at charts that show shear strength's for different sized pins, the increase in strength goes down rapidly as the size increases.

    If I remember correctly, a 1 mm solid pin (made within specs) has a shear strength of over a thousand pounds. (Edit: over 500 pounds)

    I'd be more concerned with how strong the liners are, and where the screws are placed, rather than the size of the pins.
    Last edited by Cynic2701; 03-31-2011 at 01:14 PM. Reason: Incorrect

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    What about a hollow stop pin? 1mm wall thickness?

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    Quote Originally Posted by Charlie Mike View Post
    What about a hollow stop pin? 1mm wall thickness?
    1mm wall thickness, with a hollow interior?

    The problem is that materials placed in situations of shear stress also have a range, under their shear limit, within which they will take a set (basically, they will deform).

    For maximum strength, you want solid pins. Screws are very strong, but even Chicago screws aren't as strong as a solid pin. (Imagine the inclined plane of a helix providing leverage points).

    I'm unfamiliar with what they use for knives, but since compression style locks rely on the stop pin, I'd try and get that screw changed over to a solid pin. A beefy pivot screw wouldn't hurt either

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    So reaming to a 1/4" pivot and a solid 1/4" stop pin would be best? I'm down!

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  10. #10
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    CM, have you had any Spyderco locks (liner, RIL, or compression) fail?

    To be clear, I see NOTHING wrong with enjoying the process of overbuilding something for the sake of the satisfaction it brings...I am just curious if there are many people actually cracking these locks.

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    Quote Originally Posted by Charlie Mike View Post
    So reaming to a 1/4" pivot and a solid 1/4" stop pin would be best? I'm down!
    Hahaha, yeah, I suppose that would be hard to beat.

    When you do, make sure that you don't thin out the liners/scales above the stop pin too much.

    Also, pics when you do!

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    Quote Originally Posted by Cynic2701 View Post
    Hahaha, yeah, I suppose that would be hard to beat.

    When you do, make sure that you don't thin out the liners/scales above the stop pin too much.

    Also, pics when you do!
    Sounds good! Many projects, few burners.

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    Quote Originally Posted by Kronos View Post
    I think it really comes down to the shear strength of the stop pin. At some point those screws will crack through the liner and the lock will fail. With this in mind, i dont see liner or frame making any difference
    IIRC, the stop pin, although hollow and retained by opposing screws, fits into a hole on each liner, so the shear strength of the stop pin is not dependent on the shear strength of the screws, and applying force to the stop pin wouldn't directly stress the screws. In other words, the pin is primarily held in the assembled knife by the liners, not by the screws, if that make sense. Either way, I agree that steel liners vs. titanium frame probably makes no difference. Of course, in real life, I don't think anyone has ever broken a compression lock of either variety, so this is academic at best?

  14. #14
    Ahh JNewell that makes perfect sense. so what is the limiting factor to lock strength on the compression lock? How much liner material surrounds the stop pin?

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    Frame compression lock ala the ATR?

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    Quote Originally Posted by Reeek View Post
    Frame compression lock ala the ATR?
    That seems ideal.

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  17. #17
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    Quote Originally Posted by Kronos View Post
    Ahh JNewell that makes perfect sense. so what is the limiting factor to lock strength on the compression lock? How much liner material surrounds the stop pin?
    I would guess there's a lot of variables...thickness of the tab, liners, stop pin...the material(s) they're made from...but.... -> Charlie Mike, I'm not sure this isn't gilding the lily? The compression lock, in both varieties, is probably as strong a lock as Spyderco ships...I doubt it needs added strengthening???

  18. #18
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    Three possible points of failure:

    Pivot - probably going to be equally strong in both.

    Stop pin - Probably easier to rip out of a liner than a frame (assuming 2 steel liners vs an all steel or all titanium frame)

    Lockbar - Steel does not crush easily, but a narrower piece would, at least in theory, be easier to crush than a broader one

    So, in theory, a frame compression lock "should" be stronger than a liner compression lock. However, Sal has said they can build any lock to any rating, so presuming one knife is stronger than another is presuming it was designed to be stronger.

  19. #19
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    Titanium is presumably more ductile than steel, depending a lot on which alloys are used and other variables...if I had to guess (which is all it would be) how a Ti "framelock" version of, say, the ATR compared to the steel-based "linerlock" version, I'd guess they're probably about equal, as shipped by Spyderco.

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