I have some problem with Carbide D-bit bits they don't cut nice in brass and also sometimes break, I have a simple spindle with two ballbearings and a simple bit holder it is just a hole in a steelbar and a screw that holds the bits.

So... I have read all old questions and advice it is crystal clear for me, use two flute they can drill and mill or use the more expensive end mills with radius.

Dont use carbide with a poor spindle use standard HSS as this material is a bit
tenacious and more economic.

Leffe