On 8/13/2015 11:21 AM, towertalk-request@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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