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Vertical Mast Alignment

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Subject: Vertical Mast Alignment
From: (
Date: Thu, 10 Oct 1996 11:33:39 -0400
In a message dated 96-10-10 11:05:13 EDT, you write:

>We have had several people in this area who have had binding problems using 
>thrust bearings and HyGain/CDE rotators.  The problem was that they were
>using 1
>1/2 inch pipe which is an ID dimension which, as I recall, comes out to 1.9
>OD.  Most people will just clamp in the 1.9 inch OD and without a thrust
>have no problem with the eccentricity since there is usually a lot of "slop"
>the mast exits the tower.  When the thrust bearing is added, the "slop" is 
>removed and the rotator has a real problem, especially as the rotator is
>closer to the top of the tower.
>The solution is to, first, insure the rotator is mounted in the center of
>tower.  Then, shim the mast in the rotator to insure that the mast is in the

>center of the rotator.  I don't recall what the HyGain/CDE rotators can
>for mast diameter (2 1/2 inch diameter??), but it is critical that the mast
>in the center of the clamp.  These rotators, even the Tailtwister, do not
>that much torque, and can, and do, stall if the eccentricity gets out of

Hi, Wade --

    Thanks for your  comments.  Yes, the Hy-Gain rotators are designed for 2
inch OD masts but many people use the 1.9 inch pipes because they're cheap
and available.  

    It's been my experience that by the time you add up the cumulative
tolerances in the rotator/tower plate/thrust bearing chain and consider the
fact that any load is off-center on the mast anyway, all you can hope for is
a minimum of bind.  

    As far as shimming the mast, I haven't seen a method that works and
doesn't decrease the clamping force of the Hy-Gain mast clamp.  Most people
don't do a very good job of shimming and this creates even more problems. 
>Another solution is to switch to a different rotator, like a HyGain HDR-300 
>which offers a bunch more torque than its CDE brethren and can brute force
>way through eccentricity problems that can bring a TailTwister to its knees.
     The two-piece clam shell type mast clamps that the JA rotators and M2
Orion uses as well solve a couple of problems.

>However, the HDR-300 has its limits as well.

    How true.
73 and tnx again,  Steve  K7LXC

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