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.

"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

In article , Harold and Susan Vordos says...

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.

If only a few thou of shrink is required, and the tubing is moderately
thin walled, one can do this in a (non-turning) lathe with a lever
type collet closer. Put the tubing in the collet, and snap the closer
down on it. Unsnap it, tighten the closer a bit, and snap it back
down. Continue until the tubing is at size or you need to go to the
next size down collet.

Caveats:

1) lube the collets OD before doing this

2) you need to have collets that go by 64ths, basically

3) use your oldest collets.

4) don't do this in harold's lathe....

Jim


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==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
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"jim rozen" suggested
If only a few thou of shrink is required, and the tubing is moderately
thin walled, one can do this in a (non-turning) lathe with a lever
type collet closer.

If you have access to a six-jaw chuck, you can do some nice "fluted"
neckings on thinwalled tubing. We use one to crimp shut brass tubing around
an electric match lead.

LLoyd

Current issue of Silicon Chip magazine (Australia) describes how someone
used cheap telescopic magnetic pickup tools, for Yagi elements.

Jordan

Andrew VK3BFA wrote:
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.

Hi Andrew,
The process is called metal spinning, its done on a mandrel in a lathe
or similar machine. Somehow I do not think its an easy process to get
the hang of in a few tries.

What I would do is make a sleeve with a cut in it (so its diameter can
be adjusted) and clamp that between the bigger and smaller tube. You
may have to experiment to roll the sleeve out of just the right
thickness alu for a good fit.

If I were to build a yagi big enough for the 20m band I would not use
alu tubing at all. Instead go for the fibreglass fishing rod blanks and
run a 2mm copper wire inside for the element. That would be much
lighter still and also stiffer, as the fishing rod is tapered. The
blanks come quite long, the ones I used for the cubical Quad I'd built
some years ago were over 3 m ( 12' I think) long. You could always
extend them at the centre with an alu tube epoxy glued (or sikaflexed)
to the inside of the fibreglass blank.

Have fun

Klaus VK6AKS (not active)


Andrew VK3BFA wrote:
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.

az_100 wrote:

Hi Andrew,
The process is called metal spinning, its done on a mandrel in a lathe
or similar machine. Somehow I do not think its an easy process to get
the hang of in a few tries.

What I would do is make a sleeve with a cut in it (so its diameter can
be adjusted) and clamp that between the bigger and smaller tube. You
may have to experiment to roll the sleeve out of just the right
thickness alu for a good fit.

If I were to build a yagi big enough for the 20m band I would not use
alu tubing at all. Instead go for the fibreglass fishing rod blanks and
run a 2mm copper wire inside for the element. That would be much
lighter still and also stiffer, as the fishing rod is tapered. The
blanks come quite long, the ones I used for the cubical Quad I'd built
some years ago were over 3 m ( 12' I think) long. You could always
extend them at the centre with an alu tube epoxy glued (or sikaflexed)
to the inside of the fibreglass blank.

Have fun

Klaus VK6AKS (not active)

Andrew VK3BFA wrote:
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.

Interesting idea with the fishing rods.

I think the aluminum spinning for the relatively simple task of necking
down a short section at the end of a tube is a bit less complex than a
lot of form spinning tasks.

What I would suggest trying (still requires a lathe) is to put the piece
of tubing in a suitable collet in the lathe with a few inches sticking
out. Lube and insert into the tubing, a solid rod with an OD to match
the desired ID for the tubing, this could be held in a tailstock drill
chuck. Replace the knurling rolls in a scissors type knurling tool with
plain ball bearings (smooth OD). Running the lathe at a fairly low speed
and starting closest to the collet and drawing towards the tailstock
proceed to spin the AL down until it is a snug fit on the inner mandrel.

I've not tried this myself, but since you appear to be talking about a
small amount of slop in the fit, I think this method would work.

Pete C.

Andrew VK3BFA wrote in article
. com...
Hi All,
new to this metalworking stuff, ............SNIP............. 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.


Ah, yes!

Yet another "improvement" brought about by metrification of the world......

snip
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.

So... the weakest portion of the tower is the bottom-most structure.
Sounds like you need to build another antenna tower from the "top,
down"....Or just flip the existing tower upside-down so the strongest
part is at the bottom.... G
Ken.

Ken Sterling wrote:
snip
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.

So... the weakest portion of the tower is the bottom-most structure.
Sounds like you need to build another antenna tower from the "top,
down"....Or just flip the existing tower upside-down so the strongest
part is at the bottom.... G
Ken.

Yeh, Ken - I know that - BUT logic dictates that when I climb it, I
will fall off the top. SO, if the top is the STRONGEST bit, it will
not break so I will not fall. So there......perfectly safe.... who says
engineering is complicated ....... blatantly obvious, really.....

And thank you, folks, for comments and ideas - appreciated . Swaging is
the term I needed to know. More research will be done, it might take a
while, but I will get there...If necessary, I will buy another hammer -
I have noticed that REAL engineers usually have more than one.....

Andre3w VK3BFA.

Andrew VK3BFA wrote:

I will buy another hammer - have noticed that REAL engineers usually have
I more than one.....

Never use force! Just get a bigger hammer.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

In article . com,
"Andrew VK3BFA" wrote:

it might take a
while, but I will get there...If necessary, I will buy another hammer -
I have noticed that REAL engineers usually have more than one.....


You absolutely _must_ have a Precision Adjustment/Stress-Testing Tool in
your tool collection.

An 8-pound sledge with an 18-inch handle is about right.

On 2 Dec 2005 04:40:51 -0800, "Andrew VK3BFA"
wrote:
SNIP
So... the weakest portion of the tower is the bottom-most structure.
Sounds like you need to build another antenna tower from the "top,
down"....Or just flip the existing tower upside-down so the strongest
part is at the bottom.... G
Ken.

Yeh, Ken - I know that - BUT logic dictates that when I climb it, I
will fall off the top. SO, if the top is the STRONGEST bit, it will
not break so I will not fall. So there......perfectly safe.... who says
engineering is complicated ....... blatantly obvious, really.....

Hey Andrew,

I think you had either a typo, or a misspelling there. I think you
meant you were blatantly ..........obLIvious........ to the need for
the tower to be well made all the way, but for sure the "best part"
should be the base supporting the remainder, not the other way around.

Take care.

Brian Lawson,
Bothwell, Ontario.

Andrew VK3BFA wrote:

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......

I hope that you inspected and tested your welds. Would not like to see a
steel tower falling. Guess you took some proven design.


OTOH, we had this last week here in Germany. Lots a power line towers
twisted and fell due to excessive ice load.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

Andrew VK3BFA wrote:
...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....
Andrew VK3BFA.

It's much easier to expand the smaller tubing than shrink the larger
one with hand tools. You might be able to use a small exhaust pipe
expander. I have used deep impact sockets as a form to hammer tubing
larger and make it round again.

jw

"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? -

Take the blade out of a roller pipe cutter. Spin it around a few times,
keeping it tight, then measure where it is. Slow but it works for me. To
swell out the pipe, and if its the right size, use an exhaust pipe mandrel
expander tool, from your usual auto parts stores. For smaller sizes, put in
your vise a hard rod slightly smaller than your pipe. Start hammering on
the pipe and the metal will swell out where you've been hammering. Takes
awhile to get the hang of it, though.