>> Looks like a good solution and easy to install !
>
> I never tried one of these but they get good reviews,
>
> http://www.tennadyne.com/slipp_nott.htm
I had a similar slipping problem with a HAM III and a KT34XA. I tried a
Slipp-Nott but had a VERY bad experience. It seemed to work fine for
about a year, but then after a very windy day I found the beam totally
free-wheeling.
Apparently the Slipp-Nott itself was holding fine to the mast but the
mast was still slipping in the rotor clamp. As it moved back and forth,
the brackets from the Slipp-Nott completely unscrewed the nuts from the
upper U-bolt. The lower U-bolt snapped and was pulled out of the rotor
on one side.
I have a video on my webpage showing what was found:
http://www.k9mm.com/files/Slipp-Nott.wmv
Note the piece of mast clamp hanging from one side of the broken lower
U-bolt, and the unscrewed upper U-bolt on the rotor shelf where it
landed. Note also the bent Slipp-Nott brackets.
A photo on my webpage shows the damaged U-bolt and an undamaged U-bolt
for comparison. Note how the damaged one is snapped off on one side and
bent on the other:
http://www.k9mm.com/files/Slipp-Nott.jpg
The Slipp-Nott manual is also on my webpage so you can see how it is
supposed to look when installed:
http://www.k9mm.com/files/Slipp-Nott.pdf
The tower is Rohn 25 and there is a Rohn thrust bearing above the rotor.
The KT-34XA is mounted only two feet above the thrust bearing. In order
for the lower U-bolt to be pulled out as it was, the mast must have been
tipping. I don't know how this could happen with the thrust bearing in
place, but I can't figure out how else this could have happened.
Because I no longer climb, I had to pay someone to make this emergency
repair. He removed what was left of the Slipp-Nott and apparently
tightened the new U-bolts much tighter than the originals had been
because the mast has never slipped again in the 2 1/2 years since this
happened. I guess I hadn't tightened them enough due to fear of snapping
them.
The Slipp-Nott at first seems like a good idea, but as I found it can
put too much stress on the rotor U-bolts. If I had thought to double-nut
the U-bolts, that should have prevented the nuts from being unscrewed,
but it might have caused the upper U-bolt to fracture instead. If the
mast is slipping in the rotor clamp, that force is transferred through
the Slipp-Nott brackets to the rotor U-bolts, which are not intended to
withstand that kind of load. BTW, I know of another ham nearby who also
had a Slipp-Nott failure, but I don't know exactly what happened to his
installation.
My suggestion is to use a torque wrench to tighten your rotor U-bolts to
the maximum torque allowed and see if this helps. See
http://www.engineershandbook.com/Tables/torque.htm
http://www.engineershandbook.com/Tables/torque3.htm
and http://www.zerofast.com/torque.htm
73,
John, K9MM
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