For best results, rotate vertically 180 degrees before printing. 

Tested with 38awg (0.1mm dia.)enamel coated wire, 150 turns. 2mm(h) x4mm(dia) neodymium magnet bought in bulk from aliexpress.

Core uses a m4 bolt and a press fit nut which has to be pressed in with a clamp. Any neodymium magnet stuck to the bolt would work. 

The plain bobbin by itself doesn't have a slot to hold the wire while winding, so use some electrical tape to hold it down.