At my previous job (Wall length church chimes) I had to cut Brass, aluminum & copper. We always used Titanium Nitride bits and decent cutting oil. I would also follow the above suggestion of making sure everything is square (to the bit axis), especially with these cheap drill presses.
The thing about copper is that it will "grab" the bit, and draw it into itself. When drilling copper, it's a slightly different technique as you want to barely give it any downward pressure and back it off constantly. I would also let the copper block cool down every few holes (thermal expansion). Take your time, I usually went 1/8" deep then back off, another 1/8" then back off.... as the stuff I was drilling was already too far in the manufacturing process to get a broken bit stuck inside.
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