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Saturday, February 21, 2015

CNC lathe conversion - part 2

Electric motors

I ordered two NEMA 23 425oz/in 2.8A Stepper Motor ¼” Dual shaft (KL23H286-20-8B) on eBay to run the lathe X and Z axes.

Stepper motors

When the motors came in, I was surprised to find out they didn’t fit. Fortunately that was easily fixed by enlarging the mounting holes on the drill press, and shortening the length of the shaft with a cutoff wheel.

Enlarging mounting holes

Shortening the front shaft

After mounting them on the lathe, the time came for wiring, and these motors require you to make a decision before that can be done. Since they have 2 coils per side, and 2 wires per coil, there are a total of 8 wires to be sorted out (luckily I found the wiring diagram online) into 3 possible configurations, unipolar, bipolar series, and bipolar parallel. To make a long story short, bipolar parallel is where it’s at! More torque and more speed, who wouldn’t want that! 

The point to take away here is that 8 wires give you the flexibility to chose whatever configuration you need.

Stepper motor wiring diagram

Following the diagram, I paired the wires and ended up with 4 couples to labeled A+, A-, B+ and B-. 

Wires paired for bipolar parallel configuration

These were matched to the connectors on the G540 driver unit, through one DB-9 plug per axis (X & Z).

Coils (6 though 9) and resistor (1 to 5) connections

One last item to keep in mind before being able to power them up was the addition of a resistor. Since my motors are rated for 2.8A, I needed a 2.8kΩ resistor, unable to find one, I resorted to combine random resistors until I obtained the needed value, then bridged pin 1 and 5 with it.

Making a 2.8kΩ resistor

Resistor installed between pin 1 and 5

With all the details taken care of, it was time to turn the power on, and hope it would all work out.

Testing the X and Z stepper motors

Awesome! The biggest hurdle was already behind me, though more would surely lay ahead.

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