Spindle Selection - 400Hz vs. 800Hz

I’ve seen many threads discussing spindle selection (ie. .8kw, 1.5kw, 2.2kw,…) but have not seen much if any discussing the pro’s/con’s comparing the number of poles = 2 @ 400Hz vs. poles = 4 @ 800Hz. I just purchased the HDZ for my Shapeoko Pro and although I’m interested in waiting out to see what C3D will come out with for spindle and VFD option(s) I find myself browsing AliExpress (G-Penny typical vs. “metal” working spindle) and other sources of spindles. From what I’ve read so far I’m thinking the benefit of the 4 pole spindle is it would possibly perform better at lower end RPM’s but will this also matter at the top end. No expert in this area so hopefully someone can shed some light on the matter.

A 800Hz “metal” spindle usually operates a lower RPM, typically up to 12000rpm, versus 24000rpm for the ones sold as “wood/aluminium/plastic” spindles.

I am sure others can chime in on the benefits of “high speed and low drag” when it comes to cutting forces and deflection on Shapeokos.

I chose 400Hz, 24k rpm on both of mine.

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I figured they would operate at lower RPM as well but the specifications indicate the same RPM range as the others (12000-24000 RPM) so I found that odd. Maybe it’s more about overall torque…?

I know on my RC brushless motors the more poles the higher torque but on a shapeoko you need rpm more than torque as you are not running big tooling. You would never use 2.2kw of power on a pro.

I do have a V1 65mm HD mount and a brand new never used 110v er11 Mysweety 1.5kw water cooled spindle VFD combo with a professionally soldered HD shielded spindle cable I could give you a good deal on if you are interested. The VFD is already wired with a plug for power and I have a EMI filter to go with it. I also grounded the spindle casing to the plug ground pin. You will need to program the VFD. Pm me if interested I am buying a HDM so I don’t plan to install the spindle on my So3.

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What he said,

I use my 2.2kW 400Hz 220V spindle at 1,000 RPM for edge finding, it’s stable down to about 200RPM.

I also use it for small drilling at 1,500 to 4,000 RPM depending on the size of the drill in both Aluminium and Wood, it has never got anywhere near the torque limit.

It’s true that the spindle power is much lower at low RPM but it’s still a lot more than the Shapeoko can chew.

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I was curious and found this page about pole count. It’s not as straightforward as I hoped (twice the poles = twice the torque) but much more complicated.

To make it simpler, I took two spindles from Mechatron and compared:

The 2-pole spindle has pretty constant torque so only reaches max power at max RPM.

The 4-pole spindle however has a much higher peak torque (1.6Nm vs. 0.9Nm) which it maintains from 5k to 10k RPM before falling as the power increases.

It looks like the price difference isn’t that big. 1670€ for 2-pole, 1910€ for 4-pole.

Since the 4-pole can still reach peak power at peak RPM, I’d suggest that it always makes sense to buy it if your machine can accommodate it. All it adds is extra flexibility.

I’m not 100% sure that a Shapeoko would be able to deal with the cutting forces involved though. 1.6Nm on say a 6mm tool is a lot of force (533Nm with some dumb maths), especially on a Shapeoko Pro which is still using timing belts (instead of the Shapeoko HDM which uses ballscrews).

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