[TowerTalk] welding aluminum

[Chuck Smallhouse]

Bob, N7IP,

A number of years ago I built a large multi H frame system, using 
large aluminum square booms, for a  28' long boom ,16 yagi 2M array.

I welded all of the four smaller H frames , made of square tubing (2" 
x 3") together and the and the mounting plates on the large  30' 6" 
square cross  boom  and 28' vertical risers and their mounting plates 
.  Also the perpendicular guy support tubes on the large cross and 
vertical tubing pieces.

I was a beginning welder and only had just recently taken a couple of 
welding classes at the local Jr. College.  My recently purchased 
Miller 175 amp, 220 VAC, MIG welding system, also included a recently 
released option of a spool gun for use with soft aluminium welding 
wire .  The spool gun installation instructions didn't include any 
set up temperature and speed  information regarding welding aluminum 
material .  I wrongfully assumed that it would be less than for 
steel.    Later released instructions suggested  much hotter temps 
for aluminium than for steel.  So my first few welds had to be ground 
off and redone.

TIG type of welding (by an accomplished welder), I think is a much 
better method for welding aluminum and most beautiful commercial 
aluminum welds that you see are TIGed.  However for most HB Amateur 
use, the MIG technique seems to be quite satisfactory as far as 
strength is concerned, as long as adequate weld penetration is 
achieved.  Fortunately my finish welds would not be too visible, at 
30' up in the air.  Pure argon is used for the shielding gas.

I did develope on idea/aid for use in extending and joining sections 
of the square tube to make the long boom and the long vertical 
risers.  I was very much concerned on how to accomplish perfect 
horizontal and vertical alignment of the two pieces in this 
procedure.    What I finally came up with, was to use a pencil type 
lazer pointer that I mounted on a plate, which I laid on one end of a 
section and placed a target block of wood on the other end of that 
section.  I then transferred  the target onto the far end of the 2nd, 
roughly aligned, extension piece of square tubing,  I then fine tuned 
the two pieces of tubing so that the lazer spot was dead on the 
target for the full length of the to be extended tube, hence perfect 
alignment in both H and V planes.

I then butt welded the two sections together and followed up with two 
1/4" thick x 2' long large pieces of aluminum angle along the 
diametric opposite sides of the joint, that were then also welded on 
to the two pieces.

I've found that discretely using welding techniques can not only make 
an assembly lighter but may accomplish it much quicker,  than using 
nuts and bolts and maybe with backing plates or angles.  This is 
especially true when assembling large structures for tower mounting, 
where minimum weight  and permanent alignment can be of high 
priority.  Getting rid of heavy mounting plates and multiple 
corrosion resistant U bolts can be significant, and even cost effective.

Chuck,  W7CS