The coils are formed from 16 AWG (1.3 mm diameter) tinned copper wire. Each coil has 2 bridge-overs ... Bumps
away from the surface of the cylinder to cross the neighboring coil with a minimum of capacitance.
Each coil has an associated board for tuning/matching components, a 32 MHz preamp (C13 at 3 T), Q-spoiling circuitry, a proton
trap, and connectors for RF-out and for 12 V & gnd. A separate board folds around the circumference at the cylinder base and
holds mating power connectors for distributing power to each board.
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We’ll use 3 jigs, in consecutive steps, to form the necessary wire bends for each coil:
Jig 1
Jig 3
Jig 2
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After Jig 1 step:
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After Jig 2 step:
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After Jig 3 step:
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Starting with Jig 1, cut about 24” of 16 AWG wire.
This will be plenty more than you need. You’ll cut
to length in the last step:
The idea is to use Jig 1, along with locking vise grips and clamps, to make two planar bends (the bridgeovers) in the plane of
the jig which is parallel to the floor. You don’t want to bend the wire up in the 3rd dimension ... it will work harden if you
fiddle with it too much:
There’s a feature in the
shape of a pointer here.
Put the middle of your
wire about there.
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Use locking vise grips to pull on the left end of the wire, while the far end of the jig has another vise grip
clamping the wire:
Make your first bend in the plane (no other jig fixtures should be on yet, so you’ll have room to bend the wire in the plane):
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Use a former (some piece of scrap material) to act as a pusher, so you can really bend around that corner tightly:
Tip: your partner can pull on the wire to keep the far left end of the wire in tension.
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Now add the 1st jig fixture (Lshaped with the toe of the L
pointed towards the center of Jig
1). Tighten it with a screwdriver,
making sure the bottom lip is
flush against the body of the
main jig.
Then use a clamp to hold the 1st
jig fixture on tight (as you’re
going to apply a force against it,
next).
Apply the clamp so that you have
room to keep the wire in the flat
plane throughout the next bend.
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This next bend is to pull the wire all
the way around the 1st jig fixtue in
the opposite direction from the
previous bend.
Keep the wire in tension and use your
former to make the bend tight
around the 1st jig fixture.
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Now put in the 2nd jig fixure (it’s the longer of the two
rectangles), tighen with a screwdriver such that the 2nd jig
fixture’s lip abuts flush against the body of the main jig.
Add another clamp. Again, mount the clamp so that you have
room to make the next bend also in the flat plane:
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Also apply tension to the wire before you start your bend. This next bend will
be back up and to the left.
Like this:
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Use your former while your
partner holds the wire taut.
You’ve now made one bridge-over.
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Now start working on the 2nd bridge-over. First, do the bend up around the main jig’s top extrusion, just like you did
before on the left. Use your former and keep the wire in tension:
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Screw in the 3rd jig fixture (it’s an Lshaped fixture with the toe of the L
pointed towards the center of the jig):
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...and clamp that 3rd jig fixture tight:
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Bend the wire down around that 3rd jig fixture.
Keep the wire in tension and use your former to
make the bend tight.
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Now screw in the 4th jig fixture (it’s the shorter of the two rectangles):
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Clamp the 4th jig fixture tight.
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Now your ready to bend around the 4th jig fixture:
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Bend around the 4th jig fixture, with tension, and using your former.
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Almost done. But there’s one important thing to do before removing all the clamps...
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This little plastic piece is pointing to the spot on the wire, where you need to use a magic marker
to make a mark on the wire.
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Mark the wire.
Remove the clamps. Now
you’ve got 2 bridge-overs in
the plane parallel to the floor.
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Take the wire out and mark all the way around the wire at that spot.
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This should be your result:
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We’re going to form a real 3D curve here, by the end of this 3-jig process. This Jig 2 is for bending the wire in the
perpendicular plane to the plane of the bent wire.
Place the wire so that the mark is at the apex of this oblong Jig 2.
Important: orient the wire with the bridge-over in the vertical plane.
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Adjust the locking vise grips and clamp the wire onto this Jig 2.
Note that because of the bridge-overs, you can’t pull on
the wire to put it in tension (you’ll pull out your bridgeovers). Just use your former to make the bends you
need.
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Make your bends using the former, making sure not to pull the bridge-over out:
Put in the 2nd vise grip clamp
Now you can’t pull out that
bridge-over, so put a vise
grip on the end of the wire
and pull it taut in this
direction. Use your fomer as
you bend the wire around
the neck portion of the
oblong Jig 2.
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Use a magic marker to put a marker where you’ll eventually
make the neck cut for this portion of the wire. The spot is the
outer edge of this first, closest indentation (I forgot to do it
here, and so I kludge it a few slides from now).
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Make a cut about here (doesn’t matter), and
remove the last two clamps. The bottom sproings
back, but we’ll fix that later.
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Repeat for the righthand side of the coil, making sure not to pull this bridge-over out either:
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Use the former all the way around, bending
the wire, taking care not to pull out the
bridge-over.
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Put in the 3nd vise grip clamp:
Now you can add a
vise grip clamp to
the far end of this
wire and pull it taut
in this direction.
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Cut the wire at roughly this location and
remove it from the Jig 2:
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Now for some precision touch ...
In order to get the legs parallel to each other, we’re going to make a first squeeze about ¼ of the way down from the
apex. You don’t want to overly fiddle with this wire, or it will work harden and get all wrinkly. Just one squeeze at
this point...
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...will result in this:
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Now one precision squeeze ¼ of the way up from the neck for this end of the wire:
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...will result in this:
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Now the 3rd precision squeeze for the other end of the wire:
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...will result in this:
Except for the 2 bridge-overs, we have a planar oblong coill.
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Since I forgot to mark the neck cuts earlier, I put the coil back on Jig 2. You want to mark each wire at the outer edge
of these indentations.
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The end of the wire coming down the left side of Jig 2
from the apex needs to get cut here:
The end of the wire coming down the right side
of Jig 2 from the apex needs to get cut here:
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This should be your result after Jig 2.
Next, we’d like a bend about the long axis of this oblong coil ...
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That is, right now, our coil is (except for the 2 bridge-overs), essentially flat. We want it to wrap around a cylinder:
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Simply doing something like this, doesn’t work very well.
We need Jig 3.
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Jig 3 is a half-cylinder that has a diameter of 75% of the diameter of the rat cylinder. Put Jig 3 in a drill-press vise like this
one. In this photo, we haven’t pushed down on the coil yet ... it’s still basically flat here, in a plane parallel to the floor:
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By forming this bend on a cylinder of smaller
diameter, the oblong coil will sproing back and still be
close to what we desire.
Use your fingers to press the coil into the cylindrical
shape:
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Use your former to push down on both sides of the
cyinder (without squishing your bridge-overs) to get
the wrap-around-the-cylinder shape:
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Then cut at the first mark for the neck.
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And then make the second cut at
the other neck mark:
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Keep pressing. This is the shape you want:
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This should be your result after Jig 3. The sides are lower than the apex and neck because they’ll be wrapping
around the cylinder’s girth now.
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To hold the coils in uniform positions around the rat cylinder, we need some way to hang onto each coil. In this
case, we 3D-printed a cylinder with integral clips and holes for stitching the coils into their proper locations.
Each coil has an associated board for tuning/matching components, a 32 MHz preamp (C13 at 3 T), Q-spoiling circuitry, a proton
trap, and connectors for RF-out and for 12 V & gnd. A separate board folds around the circumference at the cylinder base for
mounting the mating power connectors for distributing power to each board.
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Strategically-placed holes for Stretch Magic string (an elastomer jewelry cord) allows us to sew each coil into place.
We use 0.7 mm diameter cord, with two consecutive square knots, followed by a drop of E6000 glue.
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The string is this Stretch Magic, an elastomer jewelry cord, from Michael’s Crafts, manufactured by www.pepperell.com:
http://www.pepperell.com/Departments/Stretch-Magic.aspx
There’s a YouTube video here on how to tie off the ends (they suggest
2 to 3 consecutive square knots, followed by a drop of glue):
http://www.youtube.com/watch?v=pkz-Z8eo0VM
For glue, don’t use superglue (makes plastics brittle). Use a
general purpose adhesive such as E6000 (made by Eclectic
Products), which makes a flexible bond (it’s designed to work
on items subject to vibration, across a wide range of materials).
E6000 is available in hardware stores, at craft stores such as
Michael’s, and also at Tap Plastics.
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Once the preamp boards are stuffed with
components, two 4-40 3/16” long screws would be
used to attach them to the cylinder. Then the coil
ends would be soldered to these two pads:
The board at the bottom was fabricated on the
same panel as the preamp boards, which is thin
enough (6 mils thick Pyralux AP adhesive-less
kapton with 2 oz copper on each side) so that it
can wrap around the cylinder:
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Neighboring coils interleave under the bridge-overs:
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Close-up of the bridge-overs:
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