ChrisW
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| posted on 14/3/15 at 04:48 PM |
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Forming a spiral from tube
Hi everyone
I want to build a quadrifilar helix antenna for weather satellite reception. Something like the ones described here:
http://perso.wanadoo.es/dimoni/ant_qha.htm
To do this I need to form some 'spiral' shapes from metal tube. All the DIY efforts I have seen online look rather clumsy due to the
difficulty of forming the shape. Either people use thin wire which obviously can be bent fairly easily into the shape but can also deform quite
easily. Other suggestions have been micro-bore copper pipe, brake pipe, etc. The same issue comes up - if it's pliable enough to be bent by
hand it's not going to stand up to life outdoors in all weathers. I also need to consider that if it looks to the casual observer like there
are a load of mangled plumbing bits on the roof I'm opening myself up for a lot of earache from SWMBO!
What would be much better would be to use a stiffer material eg:
Stainless: eBay Item
Aluminium: eBay Item
...but here lies the problem, how do you form the shape accurately from a material like that? I guess some kind of jig will be needed,
I know we have loads of excellent engineers on here. Can anyone suggest a way of building something that can accurately form the curved pieces?
Perhaps it could be done on a lathe?
Cheers, Chris
My gaff my rules
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theconrodkid
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| posted on 14/3/15 at 05:40 PM |
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have a word on here http://www.mig-welding.co.uk/ they are the masters of all things metalic 
who cares who wins
pass the pork pies
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owelly
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| posted on 14/3/15 at 06:28 PM |
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Have a look at stainless Swagelok pipe (http://www.swagelok.com/products/tubing-tube-accessories/tubing.aspx). It comes in different sizes and can be
bent without too much hassle and doesn't kink easily. You can weld, braze or even silver solder it or just use the Swagelok fittings. To bend
the sort of helixeseses you want, draw the helix on a cardboard tube (wrap string/elastic round it for a guide). Carpet shops should have tubes. If
the tube is not strong enough, fill it with sand and pack it down hard.
Swagelok is a brand so there may be other stainless pipe that can be bent by hand but I've used a lot of Swagelok so I know it works!
http://www.ppcmag.co.uk
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adithorp
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| posted on 14/3/15 at 08:04 PM |
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I know nothing about this stuff so might make no sense but...
Could you not form it from something thin/easy to bend, around a former (made from 200mm plastic drain pipe) but leave the former in place (hot glue
them on) so that the aerial is a cylinder rather than an open frame? You'd have to work out a way to mount the centre piece but it'd be
more substantial and less subject to damage.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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HowardB
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| posted on 14/3/15 at 08:43 PM |
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I've seen the same thing made round the body of a pop bottle,.. also with a series of sticks in a pole,. more complex no doubt, but it would
allow for more gain.
hth
Howard
Fisher Fury was 2000 Zetec - now a 1600 (it Lives again and goes zoom)
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MikeRJ
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| posted on 14/3/15 at 08:52 PM |
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quote:
Originally posted by adithorp
I know nothing about this stuff so might make no sense but...
Could you not form it from something thin/easy to bend, around a former (made from 200mm plastic drain pipe) but leave the former in place (hot glue
them on) so that the aerial is a cylinder rather than an open frame? You'd have to work out a way to mount the centre piece but it'd be
more substantial and less subject to damage.
PVC (and some other plastics) can be quite lossy at high frequencies.
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AdrianH
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| posted on 15/3/15 at 01:40 PM |
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I have an old APT receiver and crossed circular dipole, seems to work well.
Don't use it much as the satellites are dying out, down to 3 the last I used mine. Still here and plugged in but!
Most seem to be going for the high res stuf one can get from geo stationary satellites.
Adrian
Why do I have to make the tools to finish the job? More time then money.
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Dave Ashurst
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| posted on 15/3/15 at 04:03 PM |
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Doesn't brake pipe work harden when you bend it?
If so then would it be possible to use a pipe bender to make a continuous, overlapping circular bend (like a spring) then pull it out lengthwise to
get the shape right?
Would that both achieve the shape and harden it for enough durability?
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hizzi
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| posted on 17/3/15 at 08:47 PM |
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i run a ham radio club we make antennas from alloy tube from B &Q, 8mm can be bent very accurately with a plumbers pipe bender. long sweeping
curves can be made by marking the curve on a large bit of timber then cutting the line with a jig saw, then clamp the two bits together again with the
tube in the middle, this will give consistent results
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bart
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| posted on 17/3/15 at 10:45 PM |
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copper tube
looking at the dimension's shirley ( stop calling me shirley ) 15 mm copper tube would do the trick with 90 deg elbows at each end.
you can bend "new soft" copper tube over your knee the amount you need in the picks.
you might mess a few up but its not that expensive.
if you want to get really tech cap off , fill with sand ram down till hard cap the other end off then bend away no crimping
use a piece of drain as a mandrel. you could always run a blow torch over before to anneal the tube.
with sand bet you could do larger as well.
BE ALERT > BRITAIN NEEDS LERTS
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hizzi
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| posted on 18/3/15 at 07:03 AM |
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sand is for steel pipe wont work on copper its too soft and collapses anyway, plumbers bending springs are used inside copper for 15 and 22mm external
springs ar used for 8 and 10 mm pipe
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40inches
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| posted on 18/3/15 at 09:37 AM |
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You can buy copper spirals, possibly stainless. LINK
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HowardB
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| posted on 18/3/15 at 10:01 AM |
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how about a slinky???
Howard
Fisher Fury was 2000 Zetec - now a 1600 (it Lives again and goes zoom)
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Angel Acevedo
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| posted on 18/3/15 at 03:45 PM |
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Wireline Spring Steel
Chris.
Perusing a junk yard here in my hometown, I found a coil of very bright Stainless Steel Wire about 3 or 4 mm in diameter. I was told that it was used
in Wireline Operations in oil wells.
I wanted to take home a few turns to fabricate a grille, but turned out to be VERY stiff.
Maybe you could use it cutting to length and extending on a frame. As it is very stiff, I don´t see it losing its shape once it has been welded and
fixed in place. Of course this would work if the curvature is larger than the coil. Coil diameter of the wire I found was about 80 cm.
HTH.
AA
Beware of what you wish.. for it may come true....
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