i've been having problems at times drilling some holes in copper. i got some 110 electrolyte copper, and i need a bunch of .160 holes in it. right now i'm at 1525 rpm, and a feed of 3.5 ipm. i've tried both straight drilling, and now peck driiling, but i still have problems with drills breaking. the copper is 1/2" thick and i need to go thru it with hss .160 drill. any suggestions. it doesn't happen with every part, but enough where i can't use the part because if i don't hear it break it tries to drill without a point, and ruins the part. thanks for any help.

hardinge vmc 1000