I use refrigeration tubing and have never had to use sand or any other medium
to keep its shape. I have would .25" od tubing on a 1" form with no problem.
73 Doug
N9XTF
Quoting Harold Mandel <hmandel@barantelecom.com>:
> Go to your local machine shop.
>
> Decide on the inner diameter and find a piece of PVC tubing
> that will do the job.
>
> Drill a .250 anchor hole in the side near one end.
>
> Use that hole to grab the tubing.
>
> Have the tubing laid out as flat and as straight as you can manage it.
>
> Polish the tubing while its flat. Use copper cleaner or Brasso,
> maybe a preliminary ScotchBrite treatment, but finishing the surface
> while it's flat out is much easier than doing a 35uH coil.
>
> Why are you using 1/4" stuff?
>
> Fill it with pool sand and tamp it while you're doing it with a dowel.
>
> Really pack the sand in. Crimp and solder the far end when the sand
> is pouring out from the tamping, and tamp that end, too.
>
> Chuck up the pvc tube in a lathe and use a plug for the dead end
> and jig up a live center t keep it from wobbling out.
>
> Gear down the lathe head as far as it will go.
>
> Use Yellow 77 wire pulling soap. Get a gallon bucket. Lube up
> your hands and gob it right on the tubing. Never let it run dry.
>
> Have a lathe operator start the motor and wind your choke with
> the sand-filled tubing by holding it as tightly as you can with all
> that soap, and run the coils right up on to one another.
>
> You can always trim the coil after it's off the jig. Use your LCR meter
> to see what you got.
>
> Hal
> W4HBM
>
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Dennis Ashworth
> Sent: Tuesday, November 20, 2007 4:22 PM
> To: Amps@contesting.com
> Subject: [Amps] Winding large inductors
>
> I need to construct a 35uH air inductor using .250 copper tubing. D is
> around 5"; L = 10 inches. I can play with the dia & L a bit and still be
> in the Q ballpark I desire.
>
> Does anyone have a jig or technique they use to make such a coil while
> maintaining the turn spacing and not kinking the tubing? It needs to be
> "pretty" because of where it will be located :-)
>
> Thanks
> Dennis, K7FL
>
>
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