Machine with diamond tools and cool with fluid or inner gasses to prevent combustion.
Plate after machining to prevent corrosion.
Dust is spontaneously combustable and the evolved gasses are toxic.
Hydrogen is evolved when powder is in the presence of water.
**LINK**
Best to buy the magenets you want really. They are cheap enough.
Martin
PS sound like I know about this but I just looked it up really.