Re: Need Help with 15 degree Primary Support System

In a message dated 7/15/99 2:10:19 PM Pacific Daylight Time, tesla-at-pupman-dot-com 

> Hi All,
>  I'm soliciting any tips, suggestions or hints on building a support
>  system for a 15 degree, 16 turn primary using 1/4" copper tubing 
>  for my 15kv 60ma 6" secondary system. Spacing is 1/4" between
>  turns OD, and 1/2" center-to-center. I derived the 16 turn from
>  data input into Wintesla program.
>  I had initially tried putting in 8 wooden supports at slightly more
>  than 8 inches in length to give me the 16 turns out of 1x4 for
>  the wood. I used 1/4" coax cable naildowns spacely evenly 
>  along the top of the wood but the entire affair ended up as a 
>  disaster and I had to remove everything before I actually put the
>  whole length of tubing in. The coax supports weren't deep enough
>  to hold the pipe in place when I tried a small length of pipe in 
>  them, as the tubing kept popping up and out. I used silicone
>  glue to fasten the cable holdowns to the top of the wood but this
>  proved to be a mistake. I then tried putting small brad nails through
>  the hole provided in the coax naildowns but they split the wood and
>  it also gave me a concern for providing a path to promote arcing
>  from turn to turn of the tubing. 
>  I ended up in frustration removing all the supports to start over.
>  I know there HAS to be a better method.  I would appreciate
>  any help from some of you old vet coilers on this. 
>  I also did try cutting notches into the wood 1/4" to make the
>  u-shaped channels for the tubing but I couldn't get an even
>  depth and it kept splitting the wood. Apparently using a 1x4
>  isn't necessarily a good choice of wood. 
>  Also, I need to know is it better to start the winding of the
>  tubing from inside to outside?
>  Thanks,
>  Don

I have a 6.0" diameter secondary with a 15 turn primary made from 3/8" copper 
tubing with 3/8" spacing.  I originally used a 15 to 20 degree saucer shaped 
primary and have since replaced it with a flat primary.  I would strongly 
reccomend a flat primary.  Two reasons, you can easily adjust the primary / 
secondary coupling just as well with a flat design and as the sparks grow 
ever longer the elevated primary just gets in the way.  Also, it is easier to 
build a flat primary.

I used .25" thick clear acrylic.  I bought some scraps from a local plastics 
shop and the necessary glue to put it all together.  I used a large flat 
piece for the bottom with the center cut out to clear the secondary - I used 
a 7.0" diameter hole here.  Then I made 4 pieces about 2.0" wide and as long 
as necessary and drilled 3/8" dia holes down the center in a row with each 
hole .75" apart.  Then I cut these in two pieces down the center (with a band 
saw) which yields 8 mounting pieces with notches to hold the tubing in.  Then 
I drilled 1/8" dia holes under each notch so I could hold the tubing in place 
with plastic wire ties.  Now I marked the base where the 8 supports would go 
(45 degrees apart).  Now figure out where to mount the first one so you will 
have 1.5" clearance from the secondary coil and glue it in place.  Mount the 
next support with the first notch located back about .09" (.75" / 8) from the 
first one.  Keep doing this as you go around so as the tubing is laid in, it 
will form a natural spiral with the next notch (or tie down location being 
out a little from the last one) so you gain .75" in one revolution.  I cut 
the supports off about .25" from the notch on the inside and left about 2.0" 
extra on the outside so you have some place to mount some small uprights to 
mount the strike rail on.  Once I got all the supports mounted, I cut out 
most of the plastic in between them so you have space to bring the primary 
tap lead up from underneath.  This is mounted on a roll around cart that has 
3/4" plywood mounted on the top and cutouts to match the primary base.

Now to lay the copper tubing in place - I start by supporting a flat board up 
above the coil form (about 3 or 4 feet up so you have room to work under it). 
 Lay the coil of tubing on the board and set a full gallon bucket of paint or 
something else round and heavy in the center of the coil of tubing to keep 
the coil of tubing from falling on your head.  Figure out how much tubing you 
want to go down from the innermost turn into the primary connections below 
and use a copper tubing bender (looks like a spring and cost maybe $2.50) to 
bend a tight corner there and lay the tubing into the first notch with the 
extra foot or two pointing straight down (to make it easier to work since you 
will be constancly rotating the base at this point, you might just fold this 
piece under the base and straighten it out later).  You can also start with 
just a short piece pointing down here and solder an extension on it later.  
Work the tubing into place, the natural coil of the tubing will help.  It 
really doesn't require much bending at all.  I worked one layer into place 
and then started tying the plastic wire ties into place at each notch to hold 
it.  If you keep the tubing basically in place about one revolution ahead of 
the notch you are currently tying, it works pretty smooth.  After I got a 
couple of turns tied in place I used a 3/8" diameter drill bit to check to 
make sure I had even spacing between turns.  This will take several hours and 
make your back sore but it will look great when you are done.  I used two 50 
foot coils of tubing and spliced them together right on the form as the first 
coil was used up.  Find a smaller piece of tubing that just fits into the 
tubing you are using, cut a piece about 3/8 to 1/2" long and use this piece 
to hold them together as you solder them.  Wipe off with a dry towel when the 
solder is still wet and clean up with steel wool and you won't even be able 
to find the splice.

There may still be pictures of my coil posted at Chip's web site.

Good luck and have fun,  Ed Sonderman