[TowerTalk] Joining sections of aluminum mast

[Lux, Jim]

On 8/20/22 4:08 PM, Dave KØEKL wrote:
> To ease maintenance I want to relocate my rotator to the bottom of my tower.
>
> The existing mast is 2" diameter ¼" wall 6061-T6 aluminum tubing. The rotor is 8 feet below the top of the tower / thrust bearing.
>
> What is the best way to join additional lengths of tubing together to reach the bottom? I'm thing about buying tubing that is 2" ID, cutting it into 18" or 24" sections, slitting it and slipping it over the 2" OD sections to be joined and clamping with SS U-bolt clamps like those sold by DX engineering. Will this provide enough coupling friction between sections to prevent slippage?

Much better to just get something that fits snugly inside, and run bolts 
through. The load isn't huge, so you don't need fancy bolts (the bolt is 
carrying the torque, and the weight, in shear)

Have you considered using steel pipe with standard couplings (and a jam 
nut).

How tall is the tower?

 From a torsional stiffness standpoint, large diameter, thin wall, is 
better.  I've not run the numbers, but something like 3" or 4" diameter 
irrigation tubing (or steel EMT) might not be bad. And there's off the 
shelf couplings for it. Probably something with a through pin would be 
better, though, than something that clamps. Clamps inevitably loosen, 
unless their ungalvanized steel, and they rust into place (like muffler 
clamps). Of course, removing them then requires a saw or hot wrench.



>
> Also, can I get away with using 1/8" in wall 2" OD tubing from the existing mast to the base of the tower or should I use ¼" wall all the way to the bottom.

Since tubing is basically priced by the pound, 4" tubing 1/8" wall is 
better than 2" tubing 1/4" wall - they cost about the same (same cross 
sectional area), and the 4" tubing is MUCH stiffer and stronger in a 
bending load sense.


Big and thin wall is almost always better than small and thick wall, 
except if you're holding pressure, or there's forces causing denting.



>
> Thanks.
>
> -Dave K0EKL
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