[TowerTalk] Joining masts/torquetube drive

[K7LXC@aol.com]

In a message dated 99-07-18 12:49:42 EDT, tacookfam@exotrope.net writes:

> I need to axially connect two pieces of 2"OD x 1/4" wall 6061-T6 (I know
>  - chrome-moly is stronger) for a torque-tube drive.  

      Your aluminum mast of choice has about 35kpsi yield strength which is 
suitable for modest loads and windspeeds. 

      For medium sized HF yagis or other mid-range mast torque stesses, the 
mast coupling hardware (U-bolts, saddles, etc.) will tend to gall the 
aluminum over time and the antenna(s) will start slipping on the mast. This 
problem is eliminated with a carbon steel mast.

     Mast selection is based on local windspeed conditions and antenna 
system. There are several choices between 6061-T6 (low-end) and chromoly ($$ 
high-end).

>Seems my T-twister
>  won't fit inside a 14" (face) tower section and I have to get it down to
>  the 18".  There will be ~34' inside the tower; there will be a lateral
>  thrust bearing ~10-15' down inside the tower.  I have considered using
>  an internal tube for axial alignment and a flat plate with muffler
>  clamps (four min.) to transfer the torque.

     What kind of tower is it?

     Your internal tube sounds like a good idea since you're going to have a 
long mast and some sort of coupling in there somewhere. 
>  
>  The antenna stack is a 2 wavelength 6m. beam + two 24 el. K1FO style 432
>  beams - the top of the stack is ~10' above the top of the tower (50'
>  tower) - not too bad.
>  
      Pretty modest windload-wise.

>  QTH is in the Southern tier of NY on top of a decent hill.
>  
         Steuben County is only a 70 MPH windspeed zone - the lowest rating 
they give - so no big deal wind-wise.

      Anyone wishing to find out their local windspeed rating can go to 
http://www.championradio.com and look under Tech Notes.

Cheers,   Steve   K7LXC
Tower Tech
Champion Radio Products

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