lockwasher

[rhm1]

Does including a split lockwasher in a joint require more torque than if I used a flat washer? A vendor we deal with claims that a joint with a split lockwasher under a cap screw head (tapped hole) can require up to 3-4 times the torque of the same joint with a flat washer. Is that possible? Also, am I right in assuming that the lockwasher acts like just another joint material, with a different spring constant, as you're tightening the joint?

 

[CorBlimeyLimey]

Lockwashers - To Use or Not to Use
thread404-161524

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[iainuts]

A vendor we deal with claims that a joint with a split lockwasher under a cap screw head (tapped hole) can require up to 3-4 times the torque of the same joint with a flat washer. Is that possible?

Short answer: no, he's nuts.
Long answer: The friction coefficient will be roughly the same between a flat and split washer, thus there is no significant difference between the two when it comes to torque.

Also, am I right in assuming that the lockwasher acts like just another joint material, with a different spring constant, as you're tightening the joint?

Yes, you're correct, though I don't think there's much difference in spring constant. I'd suggest you ignore the difference in diameter between the washer and split washer. The extra material on a washer is not loaded in compression.