Alternate sources for large secondary coil forms

From:  Chuck Curran [SMTP:ccurran-at-execpc-dot-com]
Sent:  Saturday, July 04, 1998 8:30 AM
To:  Tesla List
Subject:  Re: Alternate sources for large secondary coil forms

>From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
>Sent:  Friday, July 03, 1998 10:27 AM
>To:  Tesla List
>Subject:  Alternate sources for large secondary coil forms
>> If no one is aware of probs with HDPE coilforms, I suggest that
>> those of you looking for larger coilforms try commercial pipe shops
>> specializing in sewer mains...that's where I found some.  Unfortunately,
>> I'm still looking for an appropriate scrap (it comes in 40 foot
>> :-(
>> Also tends to be thick-walled and very heavy; one example of a 20 inch
>> specimen had a 0.6 inch thick wall, and the guy said it was 16 lbs/foot!!
>> On this basis, it might be a bit impractical unless one could find
>> stock.  Anybody out there finding large diameter PVC??
>> Clay
>The thick wall PVC is what you are going to find. Sewer pipes have to be
>strong enough to withstand the pressure of the soil (ask any civil
>engineer, there isn't anything called "dirt") that the pipe is buried in,
>which essentially determines the strength requirement. Sewer pipes usually
>run at atmospheric pressure, so the "bursting strength" requirement is
>For a thinner wall tube, a bit of fabrication might be required, but thin
>wall polyethylene drums are available. A couple of 50 gal drums  welded (PE
>is a pain to glue, but easy to weld) together end to end, perhaps after
>removing the heads. You could make an insert out of 1/8" or 0.100 LDPE
>strip to use as a coupler.


Jim & All:

To take Jim's suggestion one step further, I'd like to provide a short
update on the coil form I mentioned back in April.  I agree with Jim's
comment on the drums, since I have successfully completed a 23" x  100" form
winding, with turns on about 86" of the form.  The form started life as
three HDPE soap drums from a commercial laundry.  These drums had tops and
bottoms that had been inertia welded to the main cylinder/drum.  I simply
had to trim the "Lips" off the joint areas where I mated the top of one to
the bottom of the other.  I found a web site where a got the same suggestion
for HDPE could only be welded. so I tried.  I used a 200 watt soldering
iron, attached to a long stick to do the job.  I aligned the drums and then
lowered the iron down through the bung hole and created a series of joint
holes, using about 18-20 per surface.  Keep in mind here that the lid and
bottom surfaces are now acting as internal stiffeners too.  Well, the first
joint went well so I lifted the third drum up and completed that joint too.
This thing was sitting in the driveway as I did the work.  I climbed down
off the ladder and carried it into the garage just in time to see the wind
blow the form over.  The result was that several of the welds failed, but
the form was still in one piece.  I didn't plan on "dropping the completed
form, but I wasn't happy with the joint failure.  I added about 12 nylon
ty-wraps at each joint by drilling holes through each drum and with each
ty-wrap rated at 400 pounds load.  I now have a very solid form.  This joint
area turns out to look like a 2" deep V groove in the form.  The ty-wraps
can only be used if the drum caps are properly shaped.  The last step  I did
was to fill in the V groove with RTV and smoothed it out, then covered it
with a class H insulation tape.

The form is now wound and this has gone very very well.  The point I'm
trying to make here is that I believe that if you are interested in making a
larger coil form,  check out laundries for hospitals, motels/hotels or a
prison, where I got mine from!  Free is a good price in my mind.  I do have
a couple of photo's if anyone is interested.