Step #1: Wind the bobbin. PrevNext
- Place an empty bobbin onto the bobbin filler on the sewing machine. Feed the end of the copper wire into the hole at the top of the bobbin. I left about 1" of wire sticking out of the top, so I could solder the coil in place later.
- Feed the wire through the thread guide nearest to the bobbin filler. Do not use the tensioning wheel or the other guides.
- Place the spool of wire somewhere that it won’t snag, and run the sewing machine slowly. Watch the spool fill with copper wire, and apply gentle tension to the wire with your hand.
- Don’t grab the wire tightly, or you’ll cut yourself.
- When the bobbin is full, stop the machine. Hold the wire in place on the bobbin with your thumb. Cut the wire about 1" from the side of the bobbin, and then remove the bobbin from the bobbin filler.
- Remember to keep your thumb on the side of the bobbin, or the wire will unravel.
Step #2: Wrap the bobbin.PrevNext
Wrap a couple of layers of PTFE tape around the side of the bobbin. Make sure that the wire at the side of the bobbin is roughly aligned to the wire poking out of the top.
Step #3: Add plastic.PrevNext
Cut a circle of thin plastic and glue it to the bottom of the bobbin. Make sure the hole through the bobbin is blocked off on the side opposite to the wires.
Step #4: Add spring.PrevNext
Take a short length of the copper wire, and wind it around a thin screwdriver shaft to make a small spring. The spring should be about 4mm diameter, and about 3/4 the height of the bobbin.
Step #5: Add magnet.PrevNext
- Glue a 6mm magnet onto the end of a length of metal or plastic rod. I needed about 1/2" of plastic rod, so I used the shaft from an old plastic potentiometer.
- Don’t get too much glue around the edge of the shaft, or it may get wedged inside the bobbin when you fit it.
- Finally, add another dab of glue to the magnet, and glue it to the spring. Fit the spring inside the bobbin center, and fix with a bit more glue.