I had about a dozen years experience as a machinist when I took a new job at a company that manufactured resistance welding equipment. Up to that point, the only copper I ever dealt with was from a beryllium copper foundry which machined similar to CF steel. Imagine my surprise and consternation the first time I set up a 3" diameter bar of 110 grade (commercially pure) copper in a steady and the center drill "self fed" and snapped off the pilot drill section quicker than I could blink. I now was looking at having killed an expensive (several hundred dollar) piece of stock that was cut to length. :fan: Luckily an old hand came to my rescue, explaining the tool to fix the problem was already half made. The "trick" was to use a die grinder with a cut-off disk to grind a slot right down the center of the bit, right where it snapped off to about the same depth as the pilot drill length. I then stoned a negative edge on the lips of the 60 degree flute edges. This means to stone a land perpendicular drill axis, essentially removing the helical relief for a short distance. This prevents self feeding. The modified center drill was returned to the lathe and the bit was fed very slowly into the stock. It ended up going a bit deeper than the countersink area but left the broken tip exposed in a thin veneer of copper. A small punch and hammer plopped it right out. A larger center drill with a stoned negative edged on both the pilot and countersink saved the part (and perhaps my job). I had never broken a center drill before this. I learned quickly to have an entire set of drill bits (center and twist) on hand for soft copper alloys with negative edges stoned or ground at the ready. I hope this is a help to someone.