I've just finished reading the book about Spindles (Workshop Practice Series 27). I had a few questions in the process, which I was going to ask here, but had since forgotten 😀

At the end of the book there's a section on mounting and driving the spindles, the author quite categorically states that we are going to use AC and not DC motors, without any explanation of the reasons. He suggests pilfering single-phase AC motors from e.g. a washing machine, using a 4-pole motor (~1450 RPM at 50 Hz) for the milling spindles and a 2-pole one (~2900 RPM at 50 Hz) for the high-speed grinding spindle.

I'm just wondering why DC motors are immediately dismissed?

I'm planning to start with building a small high-speed spindle, something like a more robust version of the Dremel rotary tool, either with the Dremel nose, or with an ER11 collet chuck.

I was looking at brushless RC motors, these seem to be small and light, yet powerful. They do need a special speed controller (ESC) and a DC power supply. Still, it seems to be possible to build a working system very cheaply. Here are the parts I've got so far, and what I paid for them:

$28.70 from eBay SunnySky X2216 V3 1250kv brushless motor

$11.14 from eBay a 40A Brushless ESC EDIT link removed see CofC 

Other parts I have from various places, some bought, some got for free at the local recycling center (people throw out all kinds of useful electronics, including complete PCs with a nice PSU inside):

SilverStone ST85F-P 850W computer power supply, up to 67A on the single +12V rail. A few load resistors on different power rails should be used to provide the minimum required loads, specified by the manufacturer. I wonder, though, if I'm going to be using only the +12V rail, do I need the load resistors on any of the other rails?

At 12V, this motor would spin at up to 1250*12 = 15000 RPM. From what I heard, speed control should be reliable within 10%-100% range, so if 1:1 gear ratio is used, the speed range would be 1500-15000 RPM.

Control box for adjusting the speed – should be easy to build. It needs an on/off button, a potentiometer for setting the speed, and should generate a PWM signal to feed to the ESC. Getting fancy, a 7-segment 4-digit display might be added to display the theoretical RPM (or even the real one if the spindle is going to be outfitted with a tacho). I'm going to pick one of the following things I have on hand: Arduino Nano, Pro Mini, bare ATmega328P or bare ATtiny85 MCU.

The motor is of the outrunner type (the body rotates), so it might be best to put it in an enclosure for safety, and use a 12V fan to force air through the enclosure to cool it down.

I would like to hear your thoughts on pros/cons of using a DC motor (and specifically a brushless RC motor). Here's my take:

I suppose that using a plain old single-phase AC motor is really simple, could be found cheap or free, and there are no extra things required, mounting it should be simple if it already comes with a mounting base. Cons – big and heavy, fixed speed.

3-phase AC motor and a VFD: motor could be found cheap or free or bought at a relatively reasonable price, VFDs are relatively expensive unless using a noname one from China. Some extra setup required. Motor is big and heavy. Mounting should be simple.

BLDC motor, ESC, DC power supply, homemade speed controller – more parts involved. Motors and ESCs (new) are affordable, a high-current DC power supply can be expensive, but if using 12V, a cheap or free computer PSU can be used. A custom speed control box has to be made, very basic electronics and MCU knowledge required (a few Arduino tutorials should be enough). Some custom mount would need to be made.

One thing I don't like about this setup is at such a low voltage – 12V, and high current – 30A (40A peak), the power wires (and the power supply) have all to be quite beefy. The shielded power cable I got for this project is thicker/heavier than the one connecting my (small) lathe spindle's motor and VFD.

Edited By JasonB on 30/09/2020 17:24:18

Thanks for your input, everyone. Joe's devices look very cool! His motors are significantly larger than the one I've got, but I guess for the small spindle I'm planning it should be enough.