Likewise, but it depends on the weight of the mast and antennas.
In my system I'm looking at maybe 600# so I simply use one of the top
braces for the come along.
I put a saddle clamp around the mast above the bottom bearing with a
piece of angle bolted to that. I have a hold drilled through the angle
for a clevis and hook the come along to that. The bearings keep the mast
centered against any side pull. I only need to raise the mast enough to
take the pressure off the rotator plus a little for clearance which is
about an inch.
On 5/25/2010 1:58 PM, David Gilbert wrote:
> I do a similar thing, but I have a suggestion that may make it simpler
> and cheaper for you.
>
> Drill holes in one face of an 18 inch length of angle iron spaced to
> accept the bolts from a saddle-type muffler clamp (available from Pep
> Boys for a few dollars),
Although they are more, I use saddle clamps with SS bolts and an
aluminum saddle from DX engineering.
I've had poor luck using the muffler clamps rusting badly to the point
of twisting off the threaded portion if they are left in place.
Even if interrupted and you have to leave them up there for a week or
two they still get messy.
> and use that homebrew assembly instead of a
> second thrust bearing on the lower bearing plate. I use angle iron that
> is about 1.5 inches on each face, but you could use 2 inch angle iron
> and have room for two muffler clamps if you want the additional safety
> of redundancy. The muffler clamps will work fine to keep the mast from
> sliding down while you remove the rotor, and the other end of the angle
> iron can easily be secured to the bearing plate with a C-Clamp to
>
You can drill it to match one of the holes for a sure fire hold.
> prevent the mast and antennas from pinwheeling in the wind. If my
> description here is poor, let me know and I'll send you a picture of mine.
>
> Another advantage of using the angle iron and muffler clamp idea is that
> you should be able to get a crow bar between the muffler clamp and
> bearing plate to recover any minor slippage that might occur in the
> process of removing the rotor. I doubt you'd be able to do that with a
> normal thrust bearing since they sit flush on the plate.
>
> You won't want to leave the thing on the tower when you aren't using it,
> though, since the muffler clamps and bolts can rust rather quickly.
>
Boy do they ever...<:-)) That's why I went to the SS fittings. I've
never had one slip.
Normally I use a thrust bearing with the bolts loose and well greased at
the bottom accessory plate. The only time those bolts get tightened is
to hold the rotator. I also tighten the bolts in the top bearing once
the mast has been lifted so it is held it two spots. Never seize or
lubing the bolts is important as I had one TB-3 that took nearly a month
for the PB-Blaster to work in to the point where I could get the bolts
out. (I replaced them with SS)
However, the safest approach would be to lift the mast high enough to
put a block under it to prevent any injury should it slip. As I said,
I've never had one slip, but that comes with no guarantee that it won't
happen next time. Just a 2X6 or 2X8 through the tower or a piece of
steel channel wide enough for the mast to set in it will do the job.
This can also take the load off the come-along.
73
Roger (K8RI)
> 73,
> Dave AB7E
>
>
>
>
> On 5/25/2010 8:32 AM, Mark Robinson wrote:
>
>> I am thinking about possible rotor maintenance on my new tower. I will be
>> lifting a 22 foot mast and antenna stack onto the tower with a crane and
>> nesting it 4 feet or so into my Rohn 45 tower. I will have a thrust bearing
>> on the top and an Orion 2800 rotor 4 feet below the top thrust bearing.
>>
>> I am thinking of setting a second bearing plate just above the rotor which
>> will be about 4 feet below the top thrust bearing. I will have a TB3 bearing
>> on it. I may well lift this bearing off the plate and clamp it to the mast a
>> few inches above the plate so that I don't have alignment issues. The
>> bearing just sits in the air above the plate. When I want to remove the
>> rotor I should be able to lower the bearing, bolt it to the plate and add a
>> clamp to the mast so that the mast rests on this bearing or will the bearing
>> stop the mast sliding down. Some sort of u
>> bolt or a saddle clamp should work. The stack and mast will weight about 220
>> pounds.. I should be able to remove the rotor
>> then with the mast held in place. Yes it's more money but it makes it
>> possible to remove the rotor and repair it without dealing with the stack.
>>
>>
>> I am still thinking this out but I want all the pieces fabricated and
>> checked out with the tower on the ground first
>>
>>
>> Mark N1UK
>>
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