[Elecraft] [KX3] Re: Kx2 paddle issue

[Mark Goldberg]

I found this site:

https://engineerdog.com/2015/01/11/10-tricks-engineers-need-to-know-about-fasteners/

They suggest that studies show lockwashers are ineffective, but then go on
to reference other studies that show they are.

I guess is all comes down to that common answer in engineering: "It
depends". You have to design to your specific conditions, and probably
should do some dynamic testing with fatigue loads as referenced in the
article. Since I do not have testing capabilities, I use both lockwashers
and threadlocker, appropriately chosen for the application using
manufacturer's data sheets and selection guides, and hope for the best.

73,

Mark
W7MLG

On Tue, Jul 25, 2017 at 9:12 AM, Ron D'Eau Claire <ron at cobi.biz> wrote:

> It's useful to remember that a screw (or bolt) is a spring. When tightened
> it stretches lengthwise. Like any spring, it offers the best "grip" when
> subjected to the right range of pressure.
>
> Way back in my High School days (1950's - before Mercury was a toxic
> substance) I watched a demonstration using a bolt and nut made of frozen
> Mercury. Mercury is not elastic. Liquid Mercury was poured into molds for a
> nut and bolt and hardened with liquid nitrogen. Using gloves, the
> demonstrator assembled the nut and bolt using a large wrench to apply a
> great deal of torque. That done, anyone could loosen it without a wrench by
> just twisting the nut or bolt with minimal finger pressure (inside the
> gloves of course). There was no resistance since Mercury does not stretch.
>
> It's easy to over torque (stretch) small screws. That's why the Elecraft
> kit
> assembly manuals do not recommend using power screwdrivers. The Elecraft
> factory in Watsonville is equipped with special torque-limiting power
> screwdrivers to allow quick assembly with screws not so tight they are
> damaged or broken.
>
> Since a screw is basically an inclined plane that stretches the screw when
> tightened, vibration will allow the screw to turn (slide along the plane of
> the threads), hence the use of lock washers or chemical compounds in such
> environments to stop any movement.
>
> Perhaps the issue with the KX2 paddles is the vibration as the contacts
> collide allowing the screws to turn. Working remotely on the Elecraft
> manuals I've not been directly involved with the issue, so that is pure
> speculation.
>
> 73, Ron AC7AC
>
>
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