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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