[TowerTalk] Pinning mast?

David Gilbert xdavid at cis-broadband.com
Mon Nov 7 12:36:20 PST 2011

I get HUGE (often in the mid-90 mph range) clear weather wind gusts here 
in the spring.  These are thermal swirlers that can literally pull one 
end of the boom in one direction and the other end in the opposite 
direction, thereby adding in terms of torque on the mast.   I ended up 
having to pin the boom-to-mast clamps to the mast and the mast to the 
rotator clamp.   For reference, my two antennas have a total of 20 sq ft 
wind loading and boom lengths of 32 feet and 18 feet respectively.   I 
used 3/8 inch diameter grade 8 bolts (one for each clamp) available at 
Home Depot (in the specialty trays) and they have held up fine for over 
two years now.  You don't need grade 8 nuts ... standard Nyloc nuts work 
fine since all the forces on the bolt are in shear.

I think the potential advantage of using more than one bolt would be to 
help avoid the bolts reaming out the holes in the clamps or mast, but in 
my opinion the mast will retain more of it's strength if you don't align 
any of the bolt holes and separate them as much as possible.

Dave  AB7E

On 11/7/2011 12:55 PM, n8de at thepoint.net wrote:
> Steve,
> Be certain to use high-strength bolts, not the common stuff found in
> hardware stores.  You can obtain them at a farm supply store.
> Not certain .. think strength '8'?   Others will know for sure.
> 73
> Don
> N8DE
> Quoting K7LXC at aol.com:
>> Howdy --
>>      I've got a sloppy fit between a mast clamp and a  mast - both steel. It
>> won't shim properly so I think my only option is to pin  the mast. I've
>> done it a bunch of times and mostly they hold butr  sometimes they
>> don't so I'm
>> proposing to use 2 in one direction and  another two 90 degrees from the
>> first two with good-sized high strength  bolts. Other than the challenge of
>> doing it at altitude, is there anything else  I should be considering? Or is
>> there another way to do it?
>>      This is a prop pitch with big antennas on it.
>> Cheers,
>> Steve    K7LXC

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