[TowerTalk] Shorty Forty Hose Clamp thread

Howard Hoyt hhoyt at mebtel.net
Thu Aug 13 11:59:07 EDT 2015


On 8/13/2015 11:21 AM, towertalk-request at contesting.com wrote:
> Why would this be a better method than simply drilling through both
> tubes and running a machine screw all the way through and using a nylock
> nut which is a more common way to do it?

The counter-bore clamping method is ingenious and interesting, kudos to 
whomever thought of it!  A through-screw compressing both inner and 
outer tubes will distort both to a similar shape and therefore not 
really compress them against each other except directly in the area 
around the head of the screw.  The bolt then acts like an axle and lets 
the tubes pivot slightly which I have felt myself.

On the other hand bolting only the inner tube will oval it, compressing 
it inside the round outer tube over a relatively large area.  If bored 
correctly sized, the head of the cap screw will accurately locate in the 
wall of the outer tube and locate it.  I have no experience with this 
approach, but it seems to have merit.

Regarding the worm-clamp discussion: Some have commented that the normal 
clamps work good enough, which is most likely true, but that doesn't 
mean it is the best way, and I too have seen worm clamp failures while 
used on aluminum elements.  The question that went unanswered was: "what 
were they originally designed for?"  They were designed to hold 
compliant polymer hoses onto barbs, in this usage the thermal expansion 
and contraction of the hose (and barb) was taken up by the compliance of 
the hose.  When clamping metal tubing, it would be the clamp itself 
which would have to give in response to thermal expansion which would 
explain the failures seen by many including myself.  It would seem that 
the constant-torque clamps would be more suitable, if one could be found 
permitting high enough total loading:
http://www.breezehoseclamps.com/breeze/constant-torque/
I have used them on turbochargers, but I have no experience with them in 
this application.  Perhaps an investigation could prove fruitful.

Experimenting and theorizing is the path towards eliminating problems, 
but I also agree with the thought: do what you can as best as you can 
with the materials available to you...and get that antenna in the air 
and enjoy using it!

Cheers & 73!

Howie - WA4PSC




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