Pickup flatwork details

Posted on October 1, 2017

This week, a lot of students reserved time from Concordia’s Digital Fabrication Lab. I originally got a few holes cut of of an acrylic sheet I had, to see what are the appropriate dimensions for the pickup magnet, but my measures were wrong. After a few attempts at slipping between students appointments—cutting only a few holes actually takes 5-10 minutes—I managed to get the second row of holes cut. Now I know that 4.8mm is the perfect dimension to hold the magnet—which has a diameter of 4.95mm, but the laser cutter removes a bit of material when cutting.

I went back to sketching a pickup for a single magnet polepiece.

The coil wire—in red in the figure above—will be wrapped around the magnet. The coil is meant to directly connect to wires for signal and ground. Since the flatwork will be cut from non-conductive acrylic or plastic, rivets will be embedded in the flatwork so the coil wire can connect to them—the two red lines sticking out from the coil in the sketch above.

It seems Digikey has quite a few rivets, which is perfect. Another order soon on the way!

With all that in mind, I started preparing a diagram for the laser cutter. There are few things that I still have to consider:

1. The screws that will hold the plastic pieces like a sandwich around the coil require threading. Threading through such thin plastic without breaking it requires a small thread. Discussing with the metal shop technician, he suggested I look into M4-40 screws.
2. In order to dig a thread into the material, I would need the actual screw in hand to measure its dimensions and ensure the laser cutter does not remove the material needed for the threading. Which means another order after which to wait…
3. Preparing the rivet holes also require the objects in hand, although there is no need to be as fussy about dimensions here. I probably will glue the rivets to the plastic.

While the clear acrylic is practical for the prototype, I did mention earlier that I would prefer to stay away from aesthetic where all electronics are visible. I will have to look into finding some black plastic from which to cut flatworks eventually.