[TowerTalk] Broken Element Tip

[Eric Scace K3NA]

   For a small diameter piece of tubing, a large quantity of rivets is not required.  The purposes for multiple rivets are:

-- reduce degrees of freedom for movement between the two pieces of tubing.  As K7LXC pointed out, this can be done by placing the
rivet(s) at one or two locations around the circumference of the tubing.

-- increased shear and strain resistance.  This is the purpose of multiple rivets (and rivets of larger diameter) in larger pieces
of work.

   Since we are not dealing with large tubing where shear or stain forces are large, it would be adequate to place three rivets
around the circumference.

   Additional suggestion:  By staggering the distances of the rivets from the end of the larger piece of tubing (i.e., locating the
rivets in a spiral), one avoids (a) having the holes too close together and weakening the material, and (b) collisions inside the
smaller tubing between the internal pieces of the pop-rivets.

   For example, one could place a rivet 2cm from the tip on the top of the element... another rivet 3cm from the tip on the lower
lower face (120 degrees around the circumference)... and a third rivet 4cm from the tip on the rear lower face (240 degrees around
the circumference).  If more joint strength is needed, one can continue the spiral with additional rivets.

-- Eric K3NA

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com]On Behalf Of K7LXC at aol.com
Sent: 2004 May 12 01:18
To: ve5ra at sasktel.net; towertalk at contesting.com
Subject: Re: [TowerTalk] Broken Element Tip


In a message dated 5/11/04 9:17:01 PM Pacific Daylight Time,
ve5ra at sasktel.net writes:

> The tip of the reflector on a Force-12 6L 10M yagi (EF-610) broke off
>  right at the rivet.  The tip is 0.375" OD dia and 44.375" long and fits
>  into the next larger 0.50" dia section.  I suspect that it vibrated until
>  it fatigued and then fell off.  Force-12 does not mention that dampening
>  rope is needed in the element tips so none was installed.  With such a
>  small diameter of 0.375", 1/4" rope would probably not fit....maybe string
>  would work to act as a dampener?
>  Has anyone had a similar case and if so what did you do to prevent the
>  element tip from vibrating again?

    Here's what I recommend. In addition to the standard 3 rivets inline for
element attachment, add a second row of 3 (or 4) rivets opposite the original
ones. Or add a third row so that each row is 120 degrees around the element.
You'll be good to go for years now.

    The problem is that with only the single row of rivets there's still lots
of slack in the element pieces, enough for the element to work itself back
and forth and then down to the ground. Two or even three rows of rivets will
totally eliminate the wind working on the element and you'll never have to worry
about it again.

Cheers,
Steve    K7LXC
TOWER TECH -
Professional tower services for commercial and amateur
Cell: 206-890-4188
_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free,
1-800-333-9041 with any questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk