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Author Topic: Bending copper tubing for folded dipoles  (Read 4043 times)
KC2ZPK
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« on: October 15, 2012, 08:36:31 PM »


How does one bend copper, or Aluminum, tubing to form folded dipoles for UHF with out kinking the tubing? I am trying to bend some 3/8" copper tubing to form a folded dipole for UHF and I keep kinking the tubing. I haven't tried a bending spring yet, but i am not sure that will give the tight radius of about 1" I am using copper as I can solder it, as opposed to TIG welding the elements to the mounting brackets.

John
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John
KC2ZPK.com - A work in progress
WB6BYU
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« Reply #1 on: October 15, 2012, 08:57:15 PM »

Try this:  http://www.ifwtech.co.uk/g3sek/diy-yagi/dipoles.htm
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K4RVN
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« Reply #2 on: October 15, 2012, 09:23:51 PM »

John,
Harbor Freight and Northern Tool sell hand held tubing benders starting at around 12 dollars that will handle 3/8 inch OD copper tubing. In the past I have used one and they do a fair job if the bend is not too tight. I have also heard of filling the tubing with sand and taping the ends shut to hold it in. I don't know if it works but might be worth a try with the tubing bender or home built bender. I don't know if someone like ace sells the cheaper hand benders or not. I have not looked at Lowes but they just might sell one also. 3/8 plumbing copper is ID so I don't know what you need in the way of a bender size.

Frank
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K7KBN
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« Reply #3 on: October 15, 2012, 10:02:02 PM »

Why use tubing?  At UHF, solid copper wire would likely stand up just as well as tubing and be a whole lot easier to bend. 
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73
Pat K7KBN
CWO4 USNR Ret.
KD8HMB
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« Reply #4 on: October 16, 2012, 03:52:44 AM »

Try filling the hollow tube with sand or something similar. The material inide the tube will support the walls as they are being bent
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WB4SPT
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« Reply #5 on: October 16, 2012, 05:50:30 AM »

I'd try copper-weld.   Stiffness is desirable, and for UHF, the low skin depth means nil conduction in the steel.  Use those closet rack end wire pvc caps to make your aerial safe(r).
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WX7G
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« Reply #6 on: October 16, 2012, 01:52:54 PM »

Might it help to file cuts in the tubing on the inside of the bend?
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KD0REQ
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« Reply #7 on: October 16, 2012, 02:43:46 PM »

you will kink solid copper tubing trying to bend it because the material has been heat annealed in extruding it.  the bendable stuff has a thicker wall, curiously, but was not reheated after extrusion.

otherwise, if you need the stability, you will have to get a nice hot torch passed along the bend radius to resoften the copper, and preferably bend with a filler in there like fine sand.  when cooling and the color has left the copper, dip or spray it with water to anneal it again.

just for an experiment, you could try using silver solder and make the "bends" with elbow fittings.  I'm not off wire antennas yet, so haven't fiddled with self-supporting structures.
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N3QE
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« Reply #8 on: October 16, 2012, 03:00:04 PM »

Benders for conduit and pipe might give you a bend radius of like 12" in 3/8 material. But most start at the 1/2 (trade size). http://www.mcmaster.com/#conduit-benders/=jr0v74

If you need tighter, buy 4 of the 3/8" copper elbows and solder :-).  The reason you are making the antenna out of copper in the first place is because you can solder it, I guess?

Copper elbows in McMaster-Carr catalog: http://www.mcmaster.com/#catalog/118/216/=jr0udl
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MDNITERDER
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« Reply #9 on: October 16, 2012, 04:00:57 PM »

I highly recommend the rigid brand, They are not to pricy but not cheep. I have bent 3/8" .058 Wall 6061 T6 Aluminum tube with no issues at all, The other method mentioned on the first reply also works, if you make all your measurements you can pre space the spacers to give you accurate bends. I used the bender and calipers. I have actually thought about fabing up a folded dipole bender that would allow adjustable spacing and help prevent kinking like a normal tube bender.

 Good luck.

http://www.ridgid.com/Tools/400-Series-Lever-Benders


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KC2ZPK
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« Reply #10 on: October 16, 2012, 06:48:52 PM »


I tried that, but might have to try more heat. I flattened the tube around the bends. It really needs a follower to go around the bent to support the tube. I have a bender for 1 1/5" tube, but I am not sure they make dies as small as 3/8". Even if they did I could probably buy a commercial antenna for the cost of the dies.


Why use tubing?  At UHF, solid copper wire would likely stand up just as well as tubing and be a whole lot easier to bend. 

I have thought of solid copper, but almost all commercial antennas are tube, must be a reason. Wether it is a vallid reason is the question.

I highly recommend the rigid brand, They are not to pricy but not cheep. I have bent 3/8" .058 Wall 6061 T6 Aluminum tube with no issues at all, The other method mentioned on the first reply also works, if you make all your measurements you can pre space the spacers to give you accurate bends. I used the bender and calipers. I have actually thought about fabing up a folded dipole bender that would allow adjustable spacing and help prevent kinking like a normal tube bender.

 Good luck.

http://www.ridgid.com/Tools/400-Series-Lever-Benders


That tool is probably what I am looking for, has anyone used it with success? Not that I am not willing to try, just looking for options.

John
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John
KC2ZPK.com - A work in progress
W0BTU
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« Reply #11 on: October 16, 2012, 07:45:16 PM »

http://www.ridgid.com/Tools/400-Series-Lever-Benders

That tool is probably what I am looking for, has anyone used it with success? Not that I am not willing to try, just looking for options.

That's much better than using springs or sand. I used to use a tubing bender like that to bend copper tubing and even steel tubing.
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K4RVN
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« Reply #12 on: October 16, 2012, 07:58:41 PM »

John here is a Rigid tube bender on ebay you may want to check out. http://www.ebay.com/itm/Ridgid-Tools-456-Tri-Bender-1-4-5-16-3-8-O-D-Soft-Tubing-Made-USA-/140865456936?_trksid=p5197.m1997&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D16%26meid%3D2795144691156513978%26pid%3D100016%26prg%3D1006%26rk%3D2%26sd%3D230782168094%26
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N8CMQ
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« Reply #13 on: October 18, 2012, 10:00:39 PM »

What frequency are you building for?
The higher the frequency, the smaller the tubing can be.

Depending on the radius of the bend, size makes a difference.
The tighter the bend, the smaller the tubing you should use.
Pack sand and use a spring bender on the tubing for best results.

Tubing material also makes a difference in the radius of the bend.
NAPA sells a corrosion resistant brake line that is a copper/nickel
alloy which is soft and easily bent.
Air conditioning tubing is also a softer alloy and bends well, too.

Aluminum is difficult to bend, unless it is alloyed for it.
However, aluminum holds up better than copper, unless,
as noted above, you use a corrosion resistant alloy.

If strength is needed, you may want to heat treat after bending
to increase the strength. But it does cost to have it done right.

If you don't need the bandwidth larger tubing has, use wire.
Aluminum wire is light and strong, and easily worked.
Another benefit of wire is, water doesn't get inside to freeze or corrode.
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G0VKT
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« Reply #14 on: October 19, 2012, 03:03:24 AM »

Copper brake tubing is really easy to bend and form and for UHF it should be sufficiently strong enough to self support.

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