Three phase motor choice

Does anyone have any insight that might help me choose between these motors to drive my spindle? I am looking for a compact package (i.e. smallest weight or frame), but don't want to give up on speed or torque unnecessarily. It's a beefy moving gantry design and the motor is fairly far from the gantry, so weight comes at some penalty in terms of CoG and bearing loads.

The Brook Crompton goes to 90Hz which is nice, but the weight saving of the smaller TEC is significant (smaller frame). The larger TEC gives up some speed (5-70Hz), but has more power and torque at the same weight and frame of the Brook Crompton. The Universal motor might be the best compromise - similar to the smaller TEC but with higher power.

Brook Crompton 2.2kW
TEC 1.5kW
TEC 3kW
Universal 2.2kW

I'm likely to gear around 1:2-2.5, to get around max 10-12k rpm, looking at using a good range of cutter sizes (think anything that will go in ER32 collets, so 3-20mm, although it's tempting to also use shell mills and boring heads on the DIN 69871 spindle). Soft metals only. Tapping would be a bonus.

Ultimately this seems like a low risk decision as they're relatively cheap and all available in the same fitment, but I'm not a motor expert so interested to get a second opinion (and this less common way of powering a spindle is harder to read around). A servo would be nice, but I'm struggling to justify one. I'm likely to use a cheap VFD, 230V 3-phase (these notably seem a lot cheaper in 2.2kW than 3kW).

Side question, how far above the manufacturers' top rated speed is typically reasonable?

Mud,
I'm not the expert here but that 2.2Kw (3HP) motor weighs 22Kg before you add the rest of the gear you need to drive the spindle. Most of us here use a Chinese water cooled 2.2Kw spindle that is somewhat lighter and runs up to 24,000 rpm without the complexity of a pulley system and separate spindle. BST Automation (owned by the unlikely named 'Fred') is a well regarded supplier. This link shows you the package...

This spindle includes an ER20 collet chuck which will hold (if you buy a separate set of standard ER20 collets) any tool sized from 1mm to 13mm.

https://www.aliexpress.com/item/7139...348c696fzeIZSW

Kit

Quote:

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Originally Posted by Mud

Side question, how far above the manufacturers' top rated speed is typically reasonable?

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Note the Brook-Crompton's note on shaft seals at the higher quoted RPMs - clearly a cautionary note about running too fast.

Quote:

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Originally Posted by Kitwn

Mud,
I'm not the expert here but that 2.2Kw (3HP) motor weighs 22Kg before you add the rest of the gear you need to drive the spindle. Most of us here use a Chinese water cooled 2.2Kw spindle that is somewhat lighter and runs up to 24,000 rpm without the complexity of a pulley system and separate spindle. BST Automation (owned by the unlikely named 'Fred') is a well regarded supplier. This link shows you the package...

This spindle includes an ER20 collet chuck which will hold (if you buy a separate set of standard ER20 collets) any tool sized from 1mm to 13mm.

https://www.aliexpress.com/item/7139...348c696fzeIZSW

Kit

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Hi Kitwn, I've got a couple of machines with those spindles (a 2.2kW and a 3.0kW), and this time around I fancied doing it a bit differently. In my experience those spindles work well up to a 6mm cutter in aluminium, but not much further.

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Originally Posted by Doddy

Note the Brook-Crompton's note on shaft seals at the higher quoted RPMs - clearly a cautionary note about running too fast.

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Heh, true...I'm thinking the 2.2kW Universal motor is probably the winner right now as it's lighter and half the price. I've got an 85:34 pulley ratio on hand so 10.5k rpm is achievable. I guess that's still HSM, and with a decent flood setup and the high torque I hope to trouble more than just the end of the cutter ;)

Quote:

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Originally Posted by Mud

Hi Kitwn, I've got a couple of machines with those spindles (a 2.2kW and a 3.0kW), and this time around I fancied doing it a bit differently. In my experience those spindles work well up to a 6mm cutter in aluminium, but not much further.

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You could look at a Chinese spindle that has better torque low down (likely a 4 pole motor), these are sometimes called "constant power" spindles when they have torque that drops off linearly with RPM.

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Originally Posted by Voicecoil

You could look at a Chinese spindle that has better torque low down (likely a 4 pole motor), these are sometimes called "constant power" spindles when they have torque that drops off linearly with RPM.

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I would be interested to see a link (are you thinking Jianken?), but I got the impression the good ones were expensive and still lacking a bit down low. I'd happily settle for a free Mechatron like Marco Reps...look like usable performance from their 2.2kW unit from ~5,000rpm.

Full disclosure, I do have the spindle I intend to use already - if it proves a massive mistake I can swap on a different spindle later with minimal fuss. Hopefully the picture makes the point (I tried to keep the perspective fair) - it's obviously much bigger than a basic 2.2kW Chinese jobby, but not that big...80mm vs. ~110mm...so also a bit bigger than a basic 3.0kW unit (though obviously unpowered). Consider that a decent amount of the stickout is that particular toolholder, the tidy integral mount (and unpictured belt guard), 30 taper tooling, hydraulic drawbar release, reassuring derating (from 7.5kW / 20,000rpm), I can change the gearing, and that it's rated for use from 0 rpm (though I wouldn't be that mean to the bearings). Cheap, simple motors and VFDs appeal too. I'll concede it's heavy and air-cooled.

I put the 7.5kW / 8000rpm motor I took off of it on the floor, and now I can't pick it back up! :biggrin:

Quote:

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Originally Posted by Voicecoil

You could look at a Chinese spindle that has better torque low down (likely a 4 pole motor), these are sometimes called "constant power" spindles when they have torque that drops off linearly with RPM.

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You can do that with any induction motor, as it's what happens when you run out of volts to drive the motor at the intended speed. It is however actually a good way to maximise low speed torque, while still getting a high speed, as you're not as likely to need full torque at higher speeds for a low of machines.

The problem is, you can't break the basic rules of physics.
If a motor coil is rated to handle 5A, you might be able to push a bit more current through it, but push too much and it'll melt. It doesn't matter what voltage you use, if the rotor stalls, it'll likely melt.
And as Torque is direct result of current, you can't magic up more torque without pushing more current.