[TowerTalk] [Bulk] Re: Shorty Forty Hose Clamp thread

[Grant Saviers]

I'll offer a contrarian view - I don't use hose clamps or rivets. One 
exception is a pair of hose clamps when the tip of the element is 
intended to be adjusted e.g. cw to ssb.  Usually a 1/2" to 3/8" tube joint.

Riveted antennas I have acquired and rebuilt had missing and loose 
rivets.  I drilled the remaining ones out and used 2 bolts/machine 
screws per joint.  Structurally, pop rivets squeeze a joint together, 
they don't fill the holes with rivet material.  Bridge rivets (hot 
forged) and Boeing rivets do fill the hole and prevent motion (airplane 
rivets are very precise fasteners, essentially each hole is reamed to 
very tight tolerances and then the rivet is cold forged closed).  A pop 
rivet allows the tubes to move which eventually loosens the rivet or 
shears it off and it falls out.  I don't think a pop rivet can achieve 
the force needed for a "slip critical" joint - 
https://en.wikipedia.org/wiki/Slip-critical_joint

Hose clamps are for hose, not aluminum and the thread strength is poor 
(why there is this thread!).  There is no secondary resistance to 
loosening - no lockwasher, nylock, etc.

I subscribe to the Dave Leeson ("Physical Design of Yagi Antennas") bolt 
the elements together philosophy, particularly two cross bolts since the 
bolts tighten against each other as the tubing goes a bit oval from the 
force.  Nylocks or K-L nuts help keep them from loosening but cross 
bolted, they do get tight enough to stay tight. I have yet to see one 
loosen when properly tightened and then re-tightened when the connection 
stress relaxes over a few days. Cross bolts also restrain the  elements 
in two planes, just as a pair of orthogonal set screws are best for 
stuff attached to shafts.  For my 2- 3" center sections I use 5/16-18 
and for small 1/2 to 3/8 diameter joints 6-32 works fine, stepping down 
as needed as element diameters decrease - 1/4-20. 10-32. 8-32.

I use hex head bolts and then socket head (allen) for smaller sizes 
which are preferable to phillips, although one pro builder who built 
some of my antennas managed to find hex head #10 and #8 machine screws, 
but those are pretty rare.  With Penetrox on the threads of SS fasteners 
and on the overlapped tube sections, disassembly/reassembly with 
threaded fasteners is simple.  Just did that for seven large yagis that 
had been up 7 years.  Not a single fastener was loose or missing.

Grant KZ1W

On 8/8/2015 20:19 PM, john at kk9a.com wrote:
> Hose clamps come in different widths, materials and styles. I am not sure
> what MFJ/ Cushcraft uses or what failed for K6UJ, but on my homebrew
> antennas I use worm drive hose clamps with a 9/16" wide band and a 300
> series stainless steel screw.  For 1 1/4 or larger tubing I use a bolt style
> hose clamp.
>
> John KK9A
>
>
> To:	"<towertalk at contesting.com>" <towertalk at contesting.com>
> Subject:	Re: [TowerTalk] Shorty Forty Hose Clamp thread
> From:	Robert Harmon <k6uj at pacbell.net>
> Date:	Fri, 7 Aug 2015 22:02:00 -0700
>
> Doug,
>
> I no longer use hose clamps after having them strip as you had happen or the
>
> connection
> loosening after flexing back and forth in the wind (I am also in the Pacific
> NW)
> Now I only use rivets.  I have had a number of Force 12 antennas and no
> problem
> at all with the connections.  Their riveted conns sold me.  The HF beams I
> have
> fabbed have riveted elements
> and no problems.  I wipe on Penetrox when assembling and later when taking
> apart
> the tubing is like new.  Plus to change element lengths it is super easy to
> drill
> out the center of the rivets, they pop right out.  Now I can sleep easy
> while
> the winds blow,  hihi.
>
>
> 73,
> Bob
> K6UJ
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>