Making Resistive Magnets

Slow Burr

When the stamped Bitter plates return to the MagLab, the magnet makers must battle the bane of their existence: burrs.

A machine deburrs plates.

Sticklers for details, the shop's technicians seek to eliminate every little bump, ragged edge and other imperfection left behind by the stamping process. Donning plastic gloves, they send every single plate, one at a time, through a very whiny deburring machine, which works something like a planer in a woodshop, smoothing out rough spots. Then they flip each plate over and send it through the machine again. For a typical coil, this process takes several days. Patience, sharp eyes and a pair of earplugs come in handy.

What's next? More quality control! Any holes still plugged? Any uneven spots? Any foreign materials accidentally stamped into the discs? Discerning eyes check for all possible problems.

All clean and shiny and smooth, the deburred, inspected plates are then shipped out for a high-class coating of silver. Like copper, silver is a great conductor of electricity. But unlike copper, it's a soft metal, so it conducts electricity better at those points where discs touch each other.

What happens when those pretty silver plates come back? You guessed it: more deburring. Each plate is inspected yet again and any offending burrs are manually smoothed away.

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