[TowerTalk] Analysis of mast slippage in rotor

[Roger (K8RI) on TT]

On 10/1/2013 8:39 PM, Mike Reublin NF4L wrote:
> John,
>
> I have no explanation for the slippage, you didn't say if the U-bolts were loose.  The U-bolts are also available from C.A.T.S. rotor service. I would use a lock washer and/or some Loc-Tite (the removable kind).
>
> You could also bend your own from all-thread. I've bought it in the past from my local big box store. I think, without any engineering data at all, the having threads bearing on the mast would give a slightly better grip. Then there's the slipp-nott http://www.tennadyne.com/slipp_nott.htm

If you have the threading dies (two piece, not thread chasers) U-bolts 
are relatively easy to make from a piece of rod the proper length if you 
already have the saddle.  There is a bit of a learning curve though.

OTOH the u-bolt to the casing in the ham series is not very secure.

A pair of straight bolts through a 1" wide saddle or a single saddle 
long enough so that the bolt holes could line up on each end would be 
the most secure.  I don't know of any commercially available that would 
fit, but there are similar mast clamps made for large tri and mono band 
beams. The problem with straight bolts is the lack of strength in the 
upper mount of the Ham series.  I'd be more inclined to make new U-bolts 
and the matching Aluminum grips from antenna mast clamps.

Possibly you could find something close enough that it could be 
modified, or get a machine shop to make one?  If you have the dimensions 
they are relatively easy to make from a 2"thick X (what ever) block of 
Aluminum and a milling machine with an end mill.
A "one off" should only take 15 min to a half hour for set up, 
contouring and the 4 bolt holes.  Use 1/4" steps.  The critical part is 
the depth of each cut so the edges fit the mast.  Either two 1" or the 
one piece will give a far better grip than the 2 u-bolts with the metal 
stamped saddles.

Time you get a 2" X 4" X 6" block of Aluminum machined, even though this 
would be a simple set up it might be kinda pricey.
It could probably be done by machining a 1" thick piece and using 
another 1" solid piece as a backing plate. 1/2 or 1/4" steel backing 
plates should work, but then there is the rusting aspect.  Good paint job?

You might be able to adapt one of the mast mounts for the big tri or 
mono band beams.  I'll have to check the bolt spacing to my Ham IV

73

Roger (K8RI)


>
> Good luck & 73.
> Mike NF4L
>