[TowerTalk] G-1000DXA failure with lower mast clamp

[K8RI]

On 12/27/2011 9:16 AM, Barry N1EU wrote:

Grant has a good idea with the Heli-coils although you *may* have enough 
thread left for a secure hold.

Rather than lock washers I'd use medium grade "LocTite". I don't 
remember the colors now for the different strengths, but you would be 
using it just to keep the bolts from vibrating loose and their strongest 
might make it pretty difficult to remove the bolts "in place


> My G-1000DXA rotor came completely unhinged from its GC-038 lower mast
> clamp and left my 3-el Steppir and attached rotor dangling from the
> attached cables.  It appears that the attachment bolts on the bottom
> of the rotor came loose and fell out.  Please see photo at
> http://n1eu.com/g1000.jpg

Although called heavy duty the G1000 at 8# is a rather light duty 
rotator. Mast mounted it is only good for 0.75 sq meters or 8 sq ft of 
antenna and that is with the antenna mounted right on top of the 
rotator. Mounted 2' above the rotator it's only 4 sq ft. The 3L stepper 
IR is 8.1 sq foot so you are already slightly over the ratings of the 
rotator.

With the bottom of the rotator already damaged and used over it's 
ratings I'd have to think twice about using it again for the same 
conditions.

With an antenna of this size it would be a good idea to have the rotator 
mounted on a mast down inside the tower and not on top of the tower. To 
do otherwise is not safe even if it is temporary.
Mounted like this the rotator is the weak point even if the bolts don't 
fall out. That antenna is a lot of money just setting on top of a rotator.

OTOH we some times do have to do what we have to do, just remember the 
risk.  However if you have no choice but to top mount the antenna I 
would do my best to use a rotator rated for considerably more than the 
antenna actual wind load. Otherwise if you get much wind it's pretty risky.



73

Roger (K8RI)
>
> The cast aluminum fractured at one of the four threaded holes on the
> rotor bottom.  At first I thought this might be the cause of failure
> but on further thought, I would guess that the other 3 bolts came
> loose and fell away and this fourth bolt was the last to stay attached
> and this caused the aluminum fracture.  Any comments on whether this
> seems correct?
>
> I'd also appreciate comments on why this happened in the first place
> and how to prevent a repeat.  The rotor was assembled to factory
> instructions with lock washers.  Instead of using anti-seize on those
> four bolts, perhaps what is really needed is loctite?
>
> Does the motor casing need replacement and if so, is this a fairly
> easy job to do myself?  There's still about half the threads on the
> one hole that suffered the fracture.
>
> Thanks&  Happy Holidays,
> Barry N1EU
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