Repost
On 2/24/2011 11:48 AM, GEORGE BETHEA wrote:
> My 620/340 Magnum survived Katrina... 180 mph winds... downdrafts did
> snap the elements (all three 40 meter elements on one side of the
> antenna)... as they were working against the linear loading cables.
> None of the element rivets ever loosened. The largest diameter 40
> meter element tubes that extend from the boom... sheared off 4 inches
> outside of where the first rivet joint connected it to the second
> largest diameter element piece. The aluminum tubing shown signs of
> stretching (like an aluminum can bent back and forth) and that is what
> caused the failure of the tubing. It was never designed for the
> pressures of Katrina and these downbursts. The elements were almost
> pointing to the ground at times and then they would violently whip
> back into place.
> All of the rivets on the boom to element brackets were loose... only
> the 1/4x20 bolts were holding the element brackets firmly to the boom.
> I have added two additional 1/4x20 316 stainless bolts to those
> brackets... replacing 4 of the existing rivets (two on each side of
> the bracket). I also have a C49XR (120MPH version) and I followed the
> same procedure on it and without a single rivet failure. Its element
> brackets are welded in place and bolted.
> I also use Phillystran for my boom trusses as 10 years in the
> Mississippi air totally rotted the F12 cables to the point of
> failure. An N1217D has needed no such treatment and I had a C31XR up
> for about 7 years and none of this extra engineering was needed on it.
> Anyway, there is no way that an antenna can be stressed any more than
> my 620/340 was stressed during Katrina. I watched from my front porch
> as it was hammered for 12 hours... and if the element rivets held
> during that test... rest assured that I will continue with my tried
> and true modification. YMMV but it works for me... and I do love my
> F12 antennas!
> 73,
> George K5JZ
>
> --- On *Thu, 2/24/11, K8RI on TT /<k8ri-on-towertalk@tm.net>/* wrote:
>
>
> From: K8RI on TT <k8ri-on-towertalk@tm.net>
> Subject: Re: [TowerTalk] Force12 rivets
> To: towertalk@contesting.com
> Date: Thursday, February 24, 2011, 9:27 AM
>
> On 2/24/2011 8:30 AM, Gary E. Jones wrote:
> > I have a bunch of Force 12 antennas up in the air, all without
> any problems
> > for years. However, that is probably because a good friend of
> mine bought a
> > bunch before me, and rather quickly had one of the sections of
> element tips
> > simply drop to the ground. The preferred method of construction
> was to have
> > three rivets, all on positioned on the bottom of the element and
> on only one
> > side of the element. There was enough "play" in the telescoping
> elements
> > that the rivets would simply gradually be worked by the play
> until the
> > rivets dropped to the ground and the element sections worked out
> of their
> > telescoping tubing and drop to the ground also.
> >
> > MY friend (K5JZ) spent a lot of time talking with Force-12 and
> they came up
> > with the process of using 6 rivets per junction, three on one
> side of the
> > tubing and opposed by three on the other side of the tubing so
> they were 180
> > degrees apart. Placing them on opposing sides removed all the
> very small
> > "wiggle" of the elements and held them firmly in position.
> I "would think" that two or 3 sets at 120 degrees staggered with a 60
> degree offset would give the most secure connection.
>
> BTW I mentioned way earlier in this thread that my force 12's didn't
> have blind rivets, but I discovered the two packages of *spare*
> rivets
> from force 12 ARE blind rivets. Not sure why those in it aren't.
>
> OTOH I really don't see as if it'd make much difference. If properly
> seated either type should seal and if not neither type would seal
> properly.
>
> I don't like the idea of rivets on line 180 degrees apart. It makes a
> good secure connection, but at the expense of the element strength
> along
> one axis which is admittedly in a low stress area so it probably
> makes
> no difference. OTOH it would be a good idea to avoid the practice in
> higher stress (or loaded) areas.
>
> 73
>
> Roger (K8RI)
>
>
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