I’m Wound Tighter Than a Magnet’s Coil

(Apologies to Lou Barlow…)

Earlier, I explained why it is that I bought parchment paper for the lab, as part of the process of making magnetic field coils for an atom trap. What’s the actual coil-making process like? Details and pictures below the fold:

Here’s the form again:

That’s a brass pipe wrapped in parchment paper, with some cooling water lines soldered to the pipe. To turn it into a magnet, we need to put about 500 loops of wire around the pipe. This is more than I’m willing to do entirely by hand, so I took it to the machine shop, and popped it onto the lathe:

We wedged an aluminum piece into the center of the pipe, mounted it on the lathe, and hooked up a big spool of 14-gauge wire, and started winding it. Each layer of wire on the pipe amounts to about 50 turns of wire, so we need ten layers. The plastic pieces visible in the top picture are there to keep the layers confined, as they stick up a little higher than the thickness of the copper tubing.

Of course, nothing is ever as simple as you would like. The lathe we used wouldn’t go slowly enough to put the wire down cleanly. Well, maybe somebody with greater physical dexterity than I have could’ve done it, but every time I tried turning the lathe on, it went too fast, and after ten or twelve revolutions, the wire would hop back and mess up the layers, and I’d have to shut the motor off, and unwind the coil. After a few attempts, I gave up, and did it by hand– I disengaged the gears from the lathe, and rotated the head by hand, speeding up or slowing down as the winding process required.

It was fairly mindless work, but did require a fair bit of attention– every now and then, the wire would come off the spool a little bent, or the loops would start to slip, and I’d have to push everything back into place. Getting the last few loops in by the plastic guides was a real pain in the ass– those copper tubes sticking up kept getting in the way, and it was really difficult to keep the rows even. Still, it didn’t exactly require a lot of higher brain activity, which was weirdly satisfying. And, at the end of the day, I have a shiny new magnet to show for it:

(In that picture, you can see arrows on the plexiglass indicating the direction of winding, and also the messed-up last few rows at the far end of the coil. Still, I’m pretty happy with how it turned out.)

It’s not quite the end of the magnet-making saga, as I still need to glop epoxy all over it to keep the wire from unwinding the minute we cut it loose from the spool. And, of course, I need to make a second identical coil to go with this.

But, hey, shiny magnet!