I have 3 - 258 oz steppers on my Sherline mill. The spec's are 4.20 amps and 2.31 volts each. They are wired as bipolar, parallel. I know that my power supply is a bit low on voltage. It's 28 Volts / 6 Amps.
I just ran a routine to do some engine turning which was a series of quick drilling points 1/2" apart and there was about 80 in total. The Z axis was doing most of the work although I only had it set at about 3" per minute.
The problem was it was horribly hot when I was done. In fact just after it stopped the drilling routine, I jogged it and it made a bit of a grinding noise. All was well after it cooled off.
Is it possible that I'm running the voltage too low ?
Maris at Gecko advised some time ago that with a higher voltage power supply I could run the motors in series with just about zero heat sinking as things would get too warm.