I just ended up with a Shizouka NC knee mill, circa 1980. It is currently working (as of lunch time today) and on the way to my shop tomorrow. It had been down for several years due to a bad driver board, which changed out today, part of the old Bandit NC system. That is the good news.

The bad news is that 1) there is one stepper that had been getting overly? hot, and 2) I expect that I will have to retrofit the NC fairly soon, as the Bandit stuff was pretty old school, not sure how many years it will have left in it.

I am wondering if I should change the stepper that was getting hot, or if it might have been getting hot because of the driver board. There is no short to ground on any coil, and they all show similar ohm readings, though about 50% higher than the other stepper on the X. My concern is that it could burn out the replacement board if it is bad.

Secondly, what would be required to retrofit the machine? I am assuming I could get something like a Gecko drive and interface with all the existing steppers? Has Nema42 size motors, and an ATC that I would like to work. It doesn't have to be industrial, I don't have a load of parts waiting to be made, so time is easier to come by than money right now.

Hints? Thoughts? Ideas?

I'm just an electronics and CNC hobbyist and not a professional, but...

How hot does the motor actually get?

Stepper motors can normally be quite hot and still be operating within their rated limits.

Typical stepper motors that I have investigated are rated to handle as much as 80 or even 90 degrees C over ambient room temperature, which is entirely too hot to keep your hand on.

Some stepper drivers can be configured to reduce the holding current when an axis has been idle for more than a few seconds, in order to help reduce the motor heat dissipation.

That said, 1980 vintage stepper motor ratings might be different from more recent vintage motors (the typical internal geometry and wiring of stepper motors has gone through some changes since 1980).

Regardless, the motors will have a maximum rated current (which may be printed on a label affixed to the motor, otherwise if you have a part number you may be able to look it up). If the driver has been adjusted for a higher-than-rated current, that could lead to excessive heating. At or above a certain current level, the excess current no longer improves the motor's torque, but rather it just ends up being wasted in electrical losses (which translates into extra heat for no benefit).

If your stepper drivers are also of 1980's vintage, you won't be surprised to find that motor driver design has advanced since then, and so maybe a driver upgrade is in the cards for you.

The thing about Gecko drives, though, is that the ones with which I am familiar, are designed to drive bipolar motors, whereas older vintage stepper motors are probably going to be unipolar. If your motors are designed for unipolar hookup, depending on the number of wires that they have, it may be possible to rewire them for use with bipolar drivers, however due to the age of the motors (the motor design), that may not be advisable due to reduced motor performance (for example, if you were to try a half-coil hookup with the bipolar driver).