[TowerTalk] Mast slipping

[K8RI]

On 7/22/2012 10:41 PM, Rich Hallman - N7TR wrote:
> I modified mine with the hy-gain clamp.   Been up for many years and major winds with no problem.  I think those cast clamps are pretty cheap from MFJ now.
>

Cast Al tends to be quite granular and under enough pressure will 
"flake" off if the clamp slips. Once they start flaking they have less 
gripping capability under the same pressure.  I don't know if this is 
happening in this case or not.

Of course instead of casting grooved gripping surfaces ideal would be to 
fit the clamp together and bore it just a few thousandths under size, or 
bore it to an interference fit with about a 0.005 to 0.01 shim between 
the two sides. That would be a perfect fit to the mast with enough slack 
to be able to put lots of pressure on it.

Get to know a machinist in your area and/or find a small machine shop, 
tell them what you want to do and they'd probably make up or modify a 
clamp at a nominal cost.  Beware though, there can be huge differences 
in costs between machine shops and if you need a chunk of Al the size of 
a mast clamp it can get kinda pricey.   The Al mast clamp is not going 
to cut into the steel mast even with aggressive teeth. For that to work 
the mast has to be at least a little softer than the clamp.

73

Roger (K8RI)


> 73.  Rich
>
> On Jul 22, 2012, at 7:01 PM, "Gregg  Seidl" <k9kl at centurytel.net> 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.
>> Gregg  K9KL
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>