[TowerTalk] Chromoly Mast slipping in a T2X rotor

[Kim Elmore]

I've had a T2X in an HDBX 48 for 30 y. It turns a 2" diameter, 1/16" 
wall chrome-moly mast. There are 8' of mast above the thrust bearing 
holding (from top to bottom) a 40-CD2, a WD3, and KL-KT34A (a bit over 
12 sq ft). Yes, the 40 CD2 should be at the top, but... The T2X manual 
says the rotator will hold up to a 2 1/16" mast. To use a 2" mast 
requires a single 1/32" shim in the V of the mast mount on the rotator. 
I use 1/32" aluminum sheet from the hobby shop. I've have ALWAYS pinned 
the mast in the rotator and have never had an issue with it. My system 
has survived gusts up to a measured 86 MPH (I have an anemometer on the 
tower). That's not to say I'll *never* have a problem, simply that I 
haven't yet.

But, I'll also assure you that with as short a distance from the rotator 
to the thrust bearing as I have, that 1/32" shim makes the difference 
between a very long rotator life and a service life of about 2 y. I know 
from experience! If, however, a thrust bearing isn't used and, instead, 
a tube through which the mast slips (instead of a thrust bearing), no 
shim is necessary.

Kim N5OP

On 12/30/2018 9:41 AM, john at kk9a.com wrote:
> I never understood the popularity of 2" masts. Going smaller that 2" gives
> even less strength and less surface grip. I do not own a Hy-Gain rotator but
> the way I remember them is they have a metal plate the pushed the mast into
> the casting V. To center his mast he would need a 3/32 thick shim.  What
> material is the shim and does it cover the entire clamping area? Can the
> metal clamp plate bend and not allow sufficient tightening? Perhaps
> something like Tennadyne slip-nott http://www.tennadyne.com/slipp_nott.htm
> could be manufactured for his 1 7/8 mast. Perhaps there is a Stauff clamp
> that size. There is also the pinning option but that brings a lot of
> controversy - FWIW, I pinned my P40A Ø2 1/2 aluminum masts in to my Yaesu
> G-2800 DXA rotators per the manufacturer's instructions and never had an
> issue in that windy environment.
>
> 73,
> John KK9A
>
> Richard Smith n6kt wrote:
>
> A buddy of mine is using a T2X rotor with a 1 7/8" OD chromoly mast. He has
> about 13.5 sq ft of antenna surface area attached to the mast, which is well
> below the rating of 20 sq ft. The T2X is 10' below a thrust bearing.
> The mast has been slipping from time to time (windy conditions), and he was
> wondering if something can be done to stop the slippage. I have been using
> the K7NV clamp on my Orion 2800's that are clamped to 2" chromoly masts, but
> I don't see anything on Kurt's website for a T2X.
> Has anyone here on the Reflector had a similar experience and come up with a
> good solution?
> Thanks, 73, Rich, N6KT
>
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-- 

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)

/"In theory there is no difference between theory and practice. But, in 
practice, there is." //– Attributed to many people; it’s so true that it 
doesn’t matter who said it./