Trepanning cuts an annular groove into a workpiece to extract a solid cylindrical core, rather than reducing the entire hole volume to chips like a standard drill. Machinists use this method for large diameter holes or deep bores because it requires less horsepower, saves time, and preserves a usable slug of expensive stock.
Heard on the job
We need to trepan that six-inch bore so we can save the core to make the smaller flanges.
Insider tip
Trepanning tools need excellent chip evacuation, usually requiring high-pressure coolant to flush chips out of the narrow groove.