[TowerTalk] Good Fastener Practice

[Grant Saviers]

Washer/no washer?  I think it makes no difference because split 
lockwashers are pretty useless to start with.  The sharp ends should dig 
into the nut and fastened surface to prevent the nut from unscrewing.  
Of course, once flattened there is no exposed sharp end.  The other 
theory is the spring action loads a slightly loose nut's thread pitch 
with enough force that it doesn't unscrew.  Not enough spring force, so 
it doesn't work.   Flat washers do prevent digging into the fastened 
surface, which defeats part of the design.  Does make it pretty though.
https://engineerdog.com/2015/01/11/10-tricks-engineers-need-to-know-about-fasteners/

With U-bolts around antenna aluminum tubing it is doubtful that a nut 
could be tightened to its designed torque spec without damaging the 
tube.  For structural bolts that is the design and some pretty amazing 
torque values are specified for the A325 bolts.  No lockwashers are 
used.  When the threads are highly loaded the friction keeps them 
tight.  However, these fasteners are generally not subjected to high 
vibration, oscillating stress, or large temperature cycling.

So IMO, the practical ways to secure u-bolt nuts on antennas are 1. 
sleeve the tubing so it can take the stress of nuts properly torqued, 2. 
use nylocks, 3. use loctite medium grade so disassembly is possible, 4. 
use Nord-locks when vibration, stress cycling, or temperature cycling is 
expected.  Or use 360 degree split collars with straight bolts ala 
Stauff clamps instead of u-bolts. JKantennas uses custom made full 
collars on the big antennas.  DX Engineering cast saddle clamps are next 
best and very good.  U-bolts against a flat plate are a distant third.  
A u-bolt + flat plate may have only two point contacts, depending on the 
tolerances - a pretty weak connection.

Grant KZ1W

On 2/21/2018 18:57 PM, N4ZR wrote:
> I am in the process of reassembling an old F12 C3E, and noticed that 
> there were no washers with it.  Somewhere I think I recall reading 
> that when you use split lock washers, for example with U-bolts for 
> attaching elements to flat aluminum brackets, you should also use flat 
> washers between the split lock and the bracket.  True or false?
>
> 73, Pete N4ZR
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