[TowerTalk] Boom material.

[TexasRF--- via TowerTalk]

Hi Lee, one possibility is use of aluminum pipe purchased through your  
local metal supplier such as EM Jorgensen Co.
 
I built a couple of full size 3-el 40m beams about 30 years ago using the  
stuff and they survived multiple 90+ mph winds. This probably is way 
overkill  for a Moxon style beam but you asked.
 
If you start with 3.5"" OD with .3" wall material, the next smaller size of 
 2.875" OD will slip in no problem. The 2.875 material is available in 
various  wall thicknesses but for robustness, the one that is .218" thick is a 
good  choice. The two sizes can be pinned together with three or four 3/8" 
diameter  bolts.
 
The stuff comes in 20ft lengths usually so you will end up with some  
leftover material dependant on how much you telescope the pieces.
 
You can ask about different alloy choices. 6063 is commonly used for these  
large extrusions. You should be aware that the yield strength of 6063 is 
less  than 6061-T6 but the larger diameter makes 6063 useful in many  
applications.
 
In any case you likely will want to include a boom support not for strength 
 but to take out the sag, These booms are heavy!
 
I can see making the boom longer would allow adding some fore and aft  
element trusses to provide added wind survival to your Moxon.
 
73,
Gerald K5GW
 
 
 
In a message dated 5/25/2015 12:23:02 A.M. Central Daylight Time, L at w0vt.us 
 writes:

I have  been contemplating building a Moxon Yagi 40 meter beam for a long 
time and  I need to get started with the project.  The bottom line is I 
need a  strong boom 30 foot long.  I'll use a boom truss but am thinking 
of  aluminum around 3 inches in diameter and maybe 1/4 inch wall  
thickness.  I realize this won't be cheap.  Maybe this is not  even 
strong enough for a 2 element beam.  I live near Houston, so I  am 
thinking maybe an aluminum provider might be able to sell it to me in  
one piece.  (Trying to figure out how to connect affordable 6 foot  
shippable pieces has kept me stumped from starting the project up until  
now.)

I'd sure appreciate hearing suggestions on how to get the job  done. I'm 
not trying to do this on the cheap but the best reasonably  affordable 
way to do it.  I'm thinking the cost of a boom like this  might be in the 
$300 to $400 range.  (I don't mind splices, but where  to get large 
telescoping tubing?  I wrote DX Engineering and they  discouraged me from 
using their tubing as they said it was not intended  for booms even 
though I wanted to beef it up with sleeves).  Boom  diameter is a factor 
because cast boom to element clamps don't come in  every size.  (I have 
purchased heavy duty aluminum channel stock for  boom to element 
connections to be used with aluminum cast  U-clamps.)

Any help would be appreciated.

Lee, w0vt
Houston,  Texas
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