[TowerTalk] Mast slipping

[K8RI]

On 7/22/2012 10:00 PM, Gregg Seidl wrote:
> I just got down from my tower after turning my XM-240 in line to match the rotor and other antenna AGAIN.
> I have done this several times now and I just can't get a grip on why this continues to happen. I haven't had trouble with any other of my antennas,some have more windload than the XM-240.
> As I was up there enjoying the view and thinking why this one turns I had an idea and wanted to ask others ideas.
> First it is up 85 feet and has been up for 6 years and I think it works great. It is much more stout than the 40-2CD that I had up before but came down piece by piece in a bad windstorm.
> I am using the stock clamp which seems to be great,the only thing that I haven't used one other antennas but did on this one was a galvanized mast from Texas Towers. Could it be that the mast is too "smooth" to grip? The U-bolts are not loose when I go up to straighten the antenna. It only happens once a year or so nd always after a 70-80 MPH windstorm which we get here sometimes.
> Looking for ideas.

It has been my experience...which makes this completely anecdotal: 
Depending on the clamp, It's not that the galvanizing is too smooth, but 
at some point if the pressure is great enough, the galvanizing which is 
softer than the underlying mast becomes like a lubricant. Not a good 
one, but one that allows the mast clamp to slip.  I'm not sure how else 
to describe it. Under high pressure some materials flow. Given enough 
pressure almost any structural material will flow...or fracture.

"I think" what is happening is the wind reaches the point where there is 
enough leverage applied to the mast clamp that the point is reached 
where the Galvanizing can no longer hold the mast and it slips.  Inspect 
the mast where the clamp fits and see if there are places where the 
galvanizing has been abraded or is now smooth.

I think this would probably be a good place for the slipnot fixture.  It 
grips all the way around and not just at the teeth of the mount. Also 
check for the teeth being flat or rounded.

A good substitute might be to bore out a piece of malleable iron as long 
as the mount is tall, (or a tad longer-it's not critical) to the size of 
the mast (IE Interference fit) and cut/split it into two equal size 
pieces with a relatively fine or thin saw.  It only needs to be an 1/8" 
thick or even less.  It gives a very good grip on the mast over a wide 
area and the teeth on the mount can easily "dig into" the relatively 
soft iron/steel.

The down side is this material rusts easily so you might want to give 
the whole works a good coat of clear paint, plain paint,or just LPS2 
which is kinda messy, but they will prevent that big brown stain, called 
rust, from migrating down the tower.

73

Roger (K8RI)


> Gregg  K9KL
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