Winding with too much tension on the magnet wire can cause extreme side pressure on the magnets as they are wound. This can cause the magnet to crack. When the rod magnets are assembled into the flatwork to make a bobbin, the arbor or force used to press the magnets into the fixture could crack the magnet too. Another way to break magnets is when removing the coil that needs to be rewound. If a wide sharp edged blade is used to cut the coil off, the force of the blade cutting through the coil can cause the ends to be forced in and crack under the extreme pressure.