[BanduraMaker]

I'm currently using a G540 to control a 3 axis machine and I'm kinda sorta starting to maybe think about adding a Sherline 4th Axis to it.

The machine currently has the Kelling 381oz" motors and a 48v power supply. If I read correctly, the Sherline 4th comes either with a 100oz" motor or just a nema 23 mount.

Will I be able to simply plug the 100oz" motor into the G540 with the correct current set resistor or is 48v just way too high for such a dinky motor?

Should I look for a bigger 48v motor for the 4th just to be safe?

[doorknob]

I don't have actual experience with that rotary axis or motor, so this is based only on reading the specs. Some "reading between the lines" may be necessary to come up with "the answer", so excuse me while I think out loud here.

I believe that this motor:

http://www.sherline.com/stepspec2.pdf

is the one that Sherline includes with this 4th/rotary axis accessory:

CNC Rotary Table with stepper motor

According to the datasheet link above, the motor is a 6-wire type which is intended to be hooked up for unipolar operation, however you can use it with a bipolar hookup for the G540 (either by making connections to one end wire and the center tap wire of each winding, or by ignoring the center tap wires of each winding and using just the end wires).

The winding inductance (per phase) is given as 3.6 mH. My interpretation of what they mean by "per phase" of a motor intended for use in a unipolar hookup is that that inductance measurement is between one of the end wires and the center tap wire of each winding. If that is the case, and you hook up the motor to the G540 using one end wire and the center tap wire (for each winding), then the voltage formula of max V = 32 * sqr(3.6 mH) gives you a figure of around 60 volts (if I have done the math correctly).

So, if you accept that line of reasoning, then you should indeed be able to drive that motor from your G540, using your 48 volt power supply (assuming that it can supply enough amps of current). As you noted, you will have to use the appropriate current setting resistor to match the motor's current rating.