About C110|99.9% pure copper. The highest electrical conductivity of any common commercial metal (
101% IACS), which is why it’s the standard for bus bars, electrical connectors, and power distribution components. Machining it is a different story. It’s gummy, soft, and wants to stick to everything. Chips don’t break, tools load up, and drilled holes tend to mushroom at the edges. The tricks: use sharp, uncoated, positive-rake tooling (aluminum-specific inserts work well), spin fast with high feed rates but light depth of cut, and flood the coolant — oil-based at 10%+ works best. H02 (half-hard) temper machines significantly better than dead soft. Tapping is the worst part; use form taps. If you don’t need maximum conductivity and can spec C145 (tellurium copper) instead, it machines much better at only a small conductivity tradeoff. But if the print says C110, there’s usually an electrical reason.
