Re: Primaries and Copper Tubing

Subject:  Re: Primaries and Copper Tubing
  Date:   Fri, 18 Apr 1997 05:01:47 -1100
  From:   Ken Smith <ksmith-at-ihug.co.nz>
    To:   Tesla List <tesla-at-pupman-dot-com>

At 22:56 16/04/97 -0500, you wrote:
>        Right now my back hurts,  and I am frustrated,  and I'm looking
>for advice and inspiration;  and I don't even want to see
>any copper for about 24 hours.
         welcome to coiler's world. What follows is my best shot at
construction methods.  It isn't the best I am sure, but it works for me.
Hopefully there will be other replies and we shall all get something
since this is a bitch of a job at best and you are right about copper
pipe -
it's a difficult material...

Making a Primary 101 - the Flatty.

Rule 1 :  You must have a template, your eyes are not good enough to
the spacing accurate.  As far as I can tell really accurate spacing is
critical to the performance, but it looks wrong.  As a rule what looks
is and why risk the investment in time and money in making something
may not be 110%.

My most recent flatty is rather  tidy (IMHO) and it was built as
However I would make changes if I make this one again. MY variations are
[square brackets].

The base is made of a 36 inch square of 3/4 inch composite floorboard. 
template is a 8 legged star of 1/2 inch PVC pipe.  Now preping the pipe
is a
sod.  To keep the coil onto the pipes I use a hot glue gun, but the hot
doen't stick at all well to the pipe, so my marking / template had to
incorperate a keying system to the pipe [next time I will use wooden
- but I had the pipe anyway].

Marking up the pipe to privide an accurate keyway is an exercise in
patience.  I used 3/16 pipe with a 1/2 inch spacing between centers,
gives me 5/16 air space beween copper edges. This seems a reasonable
and the numbers run out.  I wanted to make a larger primary than I would
need and as I wanted (by calculation) a 14 turn I went for a 21 turn out
pipe limitation.  With a 7.5 inch center this would use two packs of
Figure out how to join the pipe with a small length of bigger pipe
you start coiling it.  

Now make up a drilling template.  My 1/2 inch spacing is easy here. 
the start leg 1, the next 7 legs have to increment the coil radius so
when the center gets back to 1 you are 1/2inch further out.  Easy - 1/16
leg.  The pipe is 3/16 OD so measure from an edge on some managable
(I use scrap 120 mil capacitor sheeting) :

| pipe  | <- 5/16 -> |       |
|   0   |            |   0   | = marks

Mark it all out for leg 1 and then drill holes on the marks.  Now lay
template onto leg 1 and pin it down starting at the point of start for
required diameter (internal).  Drill suitable sized holes into the pipe
fit plastic cocktail sticks. 

Now leg 2.  Move the template up from the starting edge by 1/16 inch and
in place.  Repeat the drilling.

Repeat for all the rest.  The leg 7 should have a start 7/16 greater
leg 1. 

Push plastic cocktail sticks into all the holes.  Easy to say...

Now lay out the legs onto the baseboard and glue down.

You will now have a very good representation of an angry sea urchin on
floor.  Find a table and put it on that (this stops back ache - since
follows really takes a while)

Take your first coil of copper out of the packet and orientate it in the
same coil direction as your template on the table.  Drill a hole
the start point of leg 1 and push through enough pipe to get the leader
to the edge of the baseboard.  This is the inner feed.  I started out
my feed on top of the board and it sparked over massively - underneath
is enough clearance.

Now carefully work the pipe inside the vertical supports formed by the
cocktail sticks.  Get a couple in and then use the glue gun to glue it
place.  Wait until the glue has hardened and then clip off the surplus
of stick.  I worked a couple at a time.  I would form the pipe
using its natural curve to avoid kinking) a 1/2 circle at a time and
glue down two at a time by putting a blob of glue onto the leg between
sticks and then holding down the pipe.  Then I would pull a larger glue
cover over the pipe between the sticks.  In this way you proceed.  It is
slow but you get a neat strong coil. The trick is to secure as you go.
Otherwise it is impossible.  

When you need more pipe, use the connection method previously
and solder it before you get the pipe end anywhere near the formed coil
you will melt the glue on the done bits !!!

When you get to the end.  Go make a coffee - you will have earnt it. 
off the fly end with one of those nice red plastic caps that came with
new pipe.

When I make my next flatty (or indeed inclined) I will use the same
but if I go for heavier pipe I will probably use wooden dowel and those
cable ties that have the tag for attaching with a screw.  The marking up
centers etc will be the same.

Hope this helps.  It isn't that comprehensive - but then no-one here has
never seen or tried a primary....  And hopefully this will be just one
many ideas for this most awkward construction task...


                              \\  ~ ~  //
                               (  -at- -at-  )
                      Ken Smith (ksmith-at-ihug.co.nz)
                             .ooo0   0ooo.
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