On Thursday, October 10, 2019 at 10:29:27 AM UTC-7, Bob La Londe wrote:
Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load. There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.

In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

Actually I am considering doing all of the above. My only real issue
with any of these things is that making the axis direct drive will
result in that huge motor (and protective cover) sticking out in front
of the machine in the way of daily operation.

I think changing the motor drive ratio is the best solution. However if one wants to get heat out of a brush dc motor i would get a non contact temperature sensor ($30 at harbor freight) and find the hot spots. The hot spots are the place to apply cooling. If the motor has plain bearing than most of the heat is being rejected though the shaft to the housing. If they are ball bearing then the heat is likely from convection of the air internal to the motor to the housing.

If you put a fan on the output shaft that blows over the motor housing you attack to heat sources. You cool the motor shaft and you cool the motor housing with force air which provides much more cooling than a static heat sink. If one need more cooling wrap copper tube around the motor and pass cold water though it.