AC Servo Motor as Spindle Questions

Hello,

I have been doing lots and lots of reading on this and I'm still a bit confused.  I recently acquired a small cnc project, it looks to be someone else's DIY.  I bought this as mainly a learning tool with the intent to make small aluminum parts, and if possible, the occasional steel piece.  Travels are just 9" on all three axis, steppers with ballscrews, and HG linear rails.  No spindle on the machine now.  My intent is to run this with Linuxcnc, mainly to learn the ins and outs, do's and don'ts, of building such a machine, because in the future (when I have the space) I would like to retrofit an older VMC.  My first thought for interfacing would be a Mesa 7i76e.  This seems sufficient to drive the steppers and has output for a spindle along with encoder input option.      

Anyway...  For the spindle, I was thinking a servo drive would be nice, rigid tapping, and position control of the spindle.  Something in the 500w to 750w region.  I would likely buy a simple ER20 or so spindle from ebay, or the Taig mill spindle.  

My initial thought was something such as this:
www.ebay.com/itm/234094923256
It is 5,000 RPM rated, I could direct drive the spindle with that and have a nice speed.  However, where I'm stuck is on the driver side of things.  The recommendation to me is to get a matched servo and driver, along with the relevant software.  So something like an allen bradley ultra 3000 drive and ultraware software.  All in, the $90 servo drive starts to look expensive.  The more I read on this forum, it seems there are some other options for universal drivers. 

• Pico systems PWM controller, this seems nice and affordable, assuming that driver works with the above servo. 
• Mesa 8i20 seems equivalent to the above, also at a good price.  I haven't done much reading to see how people power these
• I also see the Argon driver from Granite.  Big advantage to that is the nice software and simple AC input.
• And finally the ebay servo/driver combos - nicer options such as the Delta ones (closer to $500) and the $250 cheap ones have been used by a few here with good results as well?  

I would appreciate any feedback from others who have been down this path! 

Basically, I don't need the top dollar equipment here because the capabilities of this machine are limited.  However I would love to learn to control servos as that would be my goal on a retrofit of a VMC, even though maybe they are a little "extra" on this tiny machine.  

EDIT: Coming back as I learn more.  It looks like the Allen Bradley software is free.  And the Ultra 3000 drivers are plentiful, relatively cheap, and apparently very good units.  This seems again like the best way to go, but I'm open to feedback.  

Thanks!  

You won't do much rigid tapping with a direct drive motor unless it's way oversized. A decent industrial VFD (Yaskawa, Delta etc) will generate 100-150% of rated torque at zero rpm in an induction machine, so usable for rigid tapping but unless you have a spectacular motor, you'll need a reduction ratio with the encoder on the spindle. Conversely, if you can develop the torque, the max speed is likely to be fairly limited. Those high speed spindles will have a puny rated / stall torque. A 0.8kW motor of this sort appears to be claiming around 0.31Nm, presumably at base speed.
www.ato.com/800w-air-cooled-cnc-spindle-motor

Not much empirical data out there but even a modest M6 thread at 65% thread depth seems to require around 1Nm in aluminium and a #6 (M3.5) about 0.25Nm:
www.parlec.com/Products/Tapping-Tools/Sp...que-Requirements-(1)

I used a DMM Technologies DYN4 1.8kw servo as a spindle motor geared 1:1.8 for a top spindle speed of 5400. I do rigid tapping usually in the 3~6 mm range. I used a Mesa 7i76+7i83 for a +-10v interface.

John

Hi Johnny, did you encounter any problems with het buildup in the servo motor when used as a spindle motor? Did you use any additional cooling fan?

Kind regards/Stefan

I wen for a DYN4 & 750 watt AC servo, kinda wish I went a little bigger, buts that's always the case hey.

Yeah it does get a little hot, a fan probably wouldn't go astray.

Tho this is a little bonkers.

stefan63 wrote:

Hi Johnny, did you encounter any problems with het buildup in the servo motor when used as a spindle motor? Did you use any additional cooling fan?

Kind regards/Stefan

I don't have a fan on the motor.  I have had it get a little warm but never to the point where I was worried about it or thought I should check the temperature.