I'm going to try the shim idea first before drilling the clamp.
I've ordered a 5" length of 3" OD 0.0625" wall stainless steel tubing. I can
slit it with a hand grinder if I can't get it over the existing mast. I
have to figure out how to secure the mast in position and then remove the
rotator, shim the mast, and reinstall the rotator. It's going to be a
two-man job.
I had Custom Metalworks make up a rotator plate with just a 3" + hole in it
that was mounted above the rotator. It had a U-bolt saddle welded in so that
we could have clamped the mast in place. Unfortunately the hole wasn't big
enough and it didn't line up so we pulled it out to get the mast in. Now
I'll be securing the mast with angle iron and U-bolts or something along
those lines.
Dick
-----Original Message-----
From: Grant Saviers [mailto:grants2@pacbell.net]
Sent: Monday, November 07, 2011 8:25 PM
To: john@kk9a.com
Cc: TOWERTALK@contesting.com; K7LXC@aol.com; Dick Dievendorff
Subject: Re: [TowerTalk] Pinning mast?
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@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@contesting.com
> Subject: [TowerTalk] Pinning mast?
> From: K7LXC@aol.com
> Date: Mon, 7 Nov 2011 14:50:44 -0500 (EST)
> List-post:<towertalk@contesting.com">mailto:towertalk@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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>
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