[TowerTalk] Pinning mast?

[Grant Saviers]

A good question - even a pair of "slim" shims at 90 degrees apart should 
work with the compression clamp.  These can be ~2x the thickness of a 
360 deg shim and easier to drive in.  Can the clamp be spread with a 
drift or N x chisels to help get the shims in?  Or maybe several 
threaded studs with slim nuts can be backed against the inside of the 
clamp flanges although these will need to be much smaller than the clamp 
bolts in order to get the nuts to fit.

The "problem" with pins is getting the pin to hole clearance essentially 
zero - as in rivets in a Boeing airplane.  Otherwise the mast and clamp 
work against each other enlarging the hole.  The idea of a taper pin is 
reasonable since they have zero clearance, but I wouldn't want to try 
that up the tower with a #9 or 10 reamer ($$ and hard to do, step drill 
etc.).

Since the K7NV mast clamp can be deformed in one plane, if shims can't 
be placed the best bet is to add a couple of through bolts 90 deg to 
this plane.  Drill the holes a bit (1/16") undersized and use a core 
drill exactly the size of the bolts.  A core drill will essentially ream 
the hole to round and very close to diameter, even hand held.  (but I 
think any pin solution is not as good as making the clamp work +/- as 
designed).

Grant KZ1W

On 11/7/2011 4:46 PM, john at kk9a.com wrote:
> You didn't say what kind of mast clamp you are using.  While pinning a mast
> is good thing in many cases, I think you need to correct the fit of the mast
> clamp before going any further.  My prop pitch has a 3" K7NV mast clamp and
> my mast is 2 7/8 diameter so I purchased as 3" diameter stainless steel tube
> with a 1/16 wall and made a shim out of it.  The clamp then tightened to the
> mast securely.   Why won't yours shim properly?
>
> John KK9A
>
>
>
> To: towertalk at contesting.com
> Subject: [TowerTalk] Pinning mast?
> From: K7LXC at aol.com
> Date: Mon, 7 Nov 2011 14:50:44 -0500 (EST)
> List-post:<towertalk at contesting.com">mailto:towertalk at contesting.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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