I have done a couple of searches on this already, and I didn't find what I needed. Hopefully, this hasn't been hashed to death already.

Back when I built my bench CNC mill, the spindle choice was easily the most difficult and expensive among many other factors that go into a good build. At the time, the choices were pretty limited.

A good spindle (IMO) for a small bench CNC mill should have the following characteristics:

1) Very high rotational speeds... needed for small cutters. When using 1/8" to 3/8" carbide tooling, or especially engraving, RPM's north of 25,000 RPM is not a bad idea.

2) Accuracy - Anything that spins at 40K or more better have excellent bearings and proper balance. Accuracy needs to be at least very good, if not NASA-grade, as contouring with a 1/8" ball end mill will need it.

2) Variable speed. HF (high frequency 3 phase) or DC does this well

3) A common spindle nose taper. ER is excellent, IMO. Proprietary tapers or collets can be expensive.

4) Mass - the spindle/motor mass cannot be too high, as this makes Z-axis travel difficult.

5) Power - 40K RPM and high-speed motion hardware is useless if the cutter bogs down at 6 IPM. My own choice would be at least 1,000 watts, as these power measurements are usually given at high speeds, and if the spindle is running at 5K, you're not getting a kilowatt at the cutter.

With all that said, I ended up with a German-made HF spindle of 600 watts or so, and paid dearly ($$) for it. It works, but not optimally.

Fast forward a few years. There are air and water-cooled HF spindles all over eBay at ridiculous prices. Some claim "German made bearing!! ISO 9000!!" etc, and I don't know what to think.

I'd like to upgrade my spindle. Not having an ER or similar collet system is killing me. I cannot even buy a 3/16" collet for mine, and I'm limited to 1/8" and 1/4". Has anyone put one of these Chinese HF spindles into use? I would love to hear about them... they seem too good to be true, for the money. I'd like an air-cooled 1,500 watt HF spindle with an ER nose, with maybe a 60mm to 90mm body diameter.

This is the style. Prices range from $200 U.S. to $400 or so.


Also, any comments on small, precision spindles in general is welcomed.