Makerbot Z-axis Caps

This is a set of 4 caps for the tops of the 8mm threaded rods which control the Z-axis for the makerbot. I have been lugging my makerbot around in my car almost every day, and got a few scratches on the glove compartment from the rough metal rod ends. I drafted these caps in OpenSCAD, mostly to learn how to use the CSG modeling. It's a very simple part, but it's saved me any more auto interior damage.

Each cap is a cylinder with a cone segment subtracted from it. On my 'bot they screw on