"Andrew VK3BFA" wrote in message
ups.com...
Hi All,
new to this metalworking stuff, so please excuse my stupid newby
questions. I am trying to build an HF Yagi antenna from telescoping
aluminium tubing(to reduce windloading and weight) - trouble is,
Imperial size tubing was a good fit into the next size ID, so
telescopic sections could be made easily. All thats available now is
Metric sizing, and its too sloppy a fit into the next size up. HOW do I
roll/reduce the diameter of the bigger tubing so its a nice
interference fit onto the smaller size down? - whats the machine
called, can I homebrew one (I have basic hand tools, a welder, lots of
"stuffit - lets try this"...misguided enthusiasm -- well equiped
here...) - any tips, references. pointers appreciated.

PS I built the tower its going on, 8.5 metres, teaching myself to weld
as I went. Welding gets better as you go up.......so, the next logical
step is to build the antenna that goes on top of that.........

Andrew VK3BFA.


If all else fails, and it's important to swage the tubing down, you could
try pulling it through a die, then trimming it, or it can be reduced with a
complex setup of rollers set in soft jaws in a three jaw chuck. The chuck
might be mounted on the tailstock side of the cross slide, concentric and
parallel with the chuck mounted on the spindle, and should not rotate. The
stationary chuck is slowly tightened down, with the material rotating
within, with the rollers shrinking the tubing against a mandrel to control
finish size. Not good for long lengths, but adequate for fitting lengths
together if they don't need to telescope great distances.

Avoid aged (heat treated) aluminum if possible.

Harold