RE: [TCML] Secondary form material

["Jim Mora" <wavetuner@xxxxxxxxx>]

Hi Andrew,

Sorry to hear about the acrylic form cracking. It is a good choice as the
frequency gets high. HDPE and polypropylene are low loss but hard to keep
the windings secure. Polystyrene is a good, cheap choice, but hard to find
in .125". Polycarbonate is bullet proof(pun intended) but is has more loss
than acrylic at HF. Of most importance, what kind of frequencies are you
running at anyway? There are several sources on ebay for "acrylic tube".

Generally, the group concenses seems to be that .125 PVC or even thicker
wall coated with Dolphs or polyurethane, to keep moisture out of the former,
works well enough for most applications and is cheap!

There are several sites that list the dielectric strength and losses of
several plastic choices.

It would be a good engineering exercise to calculate what are acceptable
losses at your frequency!

BTW, there are several ways to safely cut acrylic. I have heard milk is a
good cutting fluid. I use a hand saw. Most people make the one time mistake
of cleaning poly or acrylic with acetone or lacquer thinner which
immediately causes chasing. Guess how I know :-)

Regards and thorough education,
Jim Mora





-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Andrew Robinson
Sent: Friday, June 26, 2009 11:58 AM
To: tesla@xxxxxxxxxx
Subject: [TCML] Secondary form material

As many have already discovered, PVC is apparently a terrible material 
to use as a secondary coil form. About a week ago my engineering group 
also discovered that acrylic is extremely hard to work with. We ended up 
cracking our only secondary coil form which we slaved over to find! So 
my question to everyone out there is what on earth should we use for the 
secondary coil form. We need a 4" OD coil form and if possible, if you 
can name a material that can also be an 1/8" thick we have a nice 
cutting tool that makes the most perfect end caps. So ideally 4" OD and 
3.75" ID is perfect for what we need. I've called numerous plumbing 
companies with no help what so ever. Thanks everyone!

Regards,
Andrew Robinson
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