Spindle options for desktop mill G0704

I have a grizzly G0704 which is a popular conversion to cnc but most people use Mach. As a Linux systems administrator I prefer Linux.

I would like to add a position controlled spindle motor. The G0704 comes with a 1HP brushed DC motor. I would like something around 1.5-2kW (2-3HP) that can do rigid tapping and will spin at 5000 rpm. I would like to spend $500 but could stretch to $800 if needed. From my research I have a few options

1) Use a brushed DC motor (treadmill motor) and add an encoder. LinuxCNC can use the encoder to position the motor. Cheap and easy. Can LinuxCNC cope with a pulley ratio on the spindle? IE if I setup a belt drive with a 1:2 ratio can I inform LinuxCNC of that and the encoder pulses will be read accordingly?

2) Use a brushless DC motor and a controller. There are a lot of e-bike and electric vehicle components that look perfect for this. The problem is most of the motors are about 8 inches wide which is too big to fit on top of my mill. I need something about 4-5 inches. It's also really hard to find a 2kW motor, there are lots of 500 watt motors and 5kW motors with nothing inbetween.

3) Use a full on servo motor with drive. I really don't know much about this despite spending over 10 hours researching it. I think I could use an AC brushless servo motor and the Mesa 8I20 card but I'm not sure what else I need. Seems like I need a 200-400v DC power supply too. The whole matching servo motors to drives seems expensive and if something breaks I would possibly need to replace both.

4) Use a VFD and a 3 phase motor with an encoder on the end. The problem with this is the 56 frame motors seem to be the only ones out there and they are too large. Is there a smaller frame size?

I'm leaning towards the servo motor with the Mesa 8I20. I can pickup a servo motor on Ebay, not worry about finding a matching drive, and I have a PC that can run a 4Khz servo thread. I'm just not sure what else I would need

If anyone else has done a position controlled spindle on the cheap I would love to hear about it. I can do 120v or 220v power but not 3 phase for the input power.

The spindle and the encoder needs to be a 1:1 ratio with one index pulse per revolution of the spindle.

I rigid tap with a regular motor and an Automation Direct GS2 VFD controlled via the gs2 component and an encoder connected to the spindle shaft.

JT

library wrote: I have a grizzly G0704 which is a popular conversion to cnc but most people use Mach. As a Linux systems administrator I prefer Linux.

I would like to add a position controlled spindle motor. The G0704 comes with a 1HP brushed DC motor. I would like something around 1.5-2kW (2-3HP) that can do rigid tapping and will spin at 5000 rpm

You do not need a positioning servo to do rigid tapping.
I do it regularly on my Bridgeport mill, with a standard VFD and induction motor. I do have
a spindle encoder with index rigged to the machine. I regularly do 4-40 and have done as
small as 2-56 taps (these are under 2mm size) with excellent results.

So, unless you have a different need for spindle positioning, you don't need a positioning servo
for threading or tapping.

I have used one of my servo amps with a DC brush motor on a minimill I drag around for
demos, and that is also capable of rigid tapping. The key point is that the Z axis
slaves to the spindle, rather than the spindle is slaved to the Z motion.

Jon

I appreciate the feedback.

I know the VFD with a 3 phase motor will work but it's just too big. I have a power drawbar that also has to go on the head and the whole head is about 5 inches wide by 9 inches deep. I've actually considered building a bigger head but that's at the bottom of my list. If I could use a VFD to drive a servo motor I would do that but I'm pretty sure I can't.

I would like to use a brushless motor if possible due to the better performance and not dealing with brushes. The servo motors are just the right size. Tall and skinny. If I could drive a servo motor like a normal brushed motor I would be all over that in a heartbeat. If they sold a tall skinny brushless DC motor then I could power it easily with an e-bike controller and an old Dell Blade Chassis power supply.

I suppose I'll probably fall back to the brushed dc motor with an encoder on the end. I just hoped there might be a better option that I've overlooked.

Is there anything the motor would need to do for rigid tapping? Does it need to stop quickly? Start quickly? What's really needed other than a simple encoder. Do I need spindle speed control or linuxcnc just slaves the z axis to whatever rpms the motor is going at?

library wrote: I would like to use a brushless motor if possible due to the better performance and not dealing with brushes. The servo motors are just the right size. Tall and skinny. If I could drive a servo motor like a normal brushed motor I would be all over that in a heartbeat. If they sold a tall skinny brushless DC motor then I could power it easily with an e-bike controller and an old Dell Blade Chassis power supply.

Well, you can get a variety of drives for brushless servo motors. Just because the motor says
"servo" on it does not mean it needs a SERVO drive! All these permanent magnet brushless
motors are very much the same inside. I make brushless servo amplifiers that could be
used to drive a spindle up to about 1 HP or so, depending on the motor's voltage.
It could be controlled with my Universal PWM Controller.

Is there anything the motor would need to do for rigid tapping? Does it need to stop quickly? Start quickly? What's really needed other than a simple encoder. Do I need spindle speed control or linuxcnc just slaves the z axis to whatever rpms the motor is going at?

library wrote: I would like to use a brushless motor if possible due to the better performance and not dealing with brushes. The servo motors are just the right size. Tall and skinny. If I could drive a servo motor like a normal brushed motor I would be all over that in a heartbeat. If they sold a tall skinny brushless DC motor then I could power it easily with an e-bike controller and an old Dell Blade Chassis power supply.

Well, you can get a variety of drives for brushless servo motors. Just because the motor says
"servo" on it does not mean it needs a SERVO drive! All these permanent magnet brushless
motors are very much the same inside. I make brushless servo amplifiers that could be
used to drive a spindle up to about 1 HP or so, depending on the motor's voltage.
It could be controlled with my Universal PWM Controller.

Is there anything the motor would need to do for rigid tapping? Does it need to stop quickly? Start quickly? What's really needed other than a simple encoder. Do I need spindle speed control or linuxcnc just slaves the z axis to whatever rpms the motor is going at?

No, too rapid starting/stopping of the spindle will make it hard for the Z axis to follow!
You want a somewhat gradual reversing at the bottom of the hole so the Z keeps
up with it. If the spindle can stop within one revolution, that may be as rapid as
you want it. You mostly just want it to stop quickly enough so you don't drive the
tap in so far the shank chews up the hole. (Rigid tapping blind holes is a bit
too nerve-wracking for me!)

You don't actually need computer spindle speed control, but it is easy enough
to do now that you might as well do it. Also, this allows the software to control
RATE of spinde reversal, which is desired. The Pico Systems brushless PWM
servo amp and PWM Controller can handle this, that't how I did it on my
minimill (although I kept the BRUSH DC motor on mine.)

Jon