Hey Nick,
if you want to mill steel, the usual spindles shown here that have two magnetic poles and a speed range from 6,000 rpm – 24,000 rpm are not the right thing. While they are excellent for high chip loads on wood, because the have constant torque up to very high speed, mostly steel is milled with rather slow speeds from 1,500 – 3,000 rpm, but with high torque. For this, I would choose a spindle with 4 or more magnetic poles (2 or more pole pairs) which are rated 3,000 – 12,000 rpm or even 1,500 – 12,000 rpm. Because of the double number of magnetic poles, at the same VFD frequency, they run at half the speed than those with 2 poles (=1 pole pair), as explained here, but with double the torque.
Examples:
- HFPD-8015-12-ER20 (Datasheet with speed/torque diagram) (4 magnetic poles, 1,500 – 12,000 rpm)
- HFPM-8022-24-ER20 (Datasheet with speed/torque diagram) (4 magnetic poles, 3,000 – 24,000 rpm)
- ATC-12575-12 (4 magnetic poles, 1,500 – 12,000 rpm)
For comparison, a spindle with 2 magnetic poles with characteristic as the most spindles shown here (good for wood):
- HFS-8022-24-ER20 (Datasheet with speed/torque diagram) (2 magnetic poles, 6,000 – 24,000 rpm)
Compare the speed/torque diagram on the bottom of all the datasheets!
Pole pairs on three-phase asynchronuous induction motors:
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| 2 magnetic poles (1 pole pair) | 4 magnetic poles (2 pole pairs) |
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