(NEWBIE) How to use an (Fanuc) AC Spindle servo motor for an DIY CNC router

11 Mar 2017 17:21 #89426 by denhen89
Hello everyone,
my name is Denis and its my first thread/post here.

In near future (1-3month) i want to start build an "fixed gantry" CNC router for machining Steel and Aluminium. Unfortunately i have no experience at all, at least no practical. (just reading all the time about milling and cnc for about one and half month)

I want to make this post as short as possible, because i dont think it makes much sense to write about my whole idea. Usually i try always to solve my problems without asking for others (looking for information through google), but im really stuck at this for at least 4 days and i really need help. I have already ask that same thing in cnczone and in an polish cnc forum, but i get no answer or no help, so maybe you are my last chance and to be honest even if it will take at least 1-3 month before start, i would like already no if that is possible to realize or not. I would like to learn Solidworks by drawing the cnc router, but due to this problem i see no sense to start.

So, here what i want ask:
Is it possible to use an year 1995 - Fanuc AC Spindle motor on an new system which runs with LinuxCNC ? I mean, without the original boards, drives, etc..? That is exactly the spindle motor: Fanuc 3S-12000 Its an 4 pole, 3phase, 3,7kw / 5.5kw, 1.500rpm - 12.000 rpm AC spindle motor with over 20Nm torque. The parameters (rpm, power, torque) are just perfect for what i plan to do (steel and aluminium machining) and this motor should be connected through an chain or strong belt to an ATC BT30 Belt drive Spindle with max. 12.000 rpm. In future i want to have that option to do rigid tapping and have an ATC.

Of course i tryed to do my homework by my own like i already wrote, but i couldnt find anything which gives me an 100% guarantee that it works and how exactly. Always i found posts where poeple wanted to retrofit old lathes or milling machines, but that was poeple who had already experience.

I looked for the MESA cards/boards and it sounds like its possible to do with the 7i77 and 5i25 cards (plug and go), but still, i need some spindle drive or VFD ?

Guys, i really tryed everything and i have such an headache. It doesnt matter anymore what i write in google search, almost every link got already clicked..

Thanks in advance.

Best Regards,
11 Mar 2017 22:03 - 11 Mar 2017 22:04 #89432 by rodw
Denis, I'm sure it can be done but I don't know how. I do know that if Mesa don't have a solution, Pico Systems has some Fanuc servo drivers that work with LinuxCNC. See
Last Edit: 11 Mar 2017 22:04 by rodw.
11 Mar 2017 22:06 #89433 by PCW
Pretty sure that's a standard AC induction motor so can be drive with a normal VFD
11 Mar 2017 22:14 #89436 by denhen89
Thank you very much for your reply!

@rodw: I wrote with someone from Pico and to my question regarding the spindle motor i got this answer:
"The motor ratings are confusing, 1500 and 12000 RPM. Does it have two sets of windings?
Anyway, as it is a 200 V motor, our servo amplifier can't be used with it. Possibly a higher-end VFD can drive this motor."

@PCW: I was sure it was an servo motor, sorry. But what does it exactly mean if that is an AC Induction motor? I mean, is it then possible to do rigid tapping and use an ATC ? Its not something i need straight way, but i would like to have that option to use it in future, without changing the spindle motor or VFD,
If i just need an VFD, then that shouldnt be a big problem to get it to work, right? Would this VFD work: machmotion.com/cnc-products/drives-motor...drive-7-5hp-805.html

Thanks in advance!
11 Mar 2017 22:34 #89438 by tommylight
The first result has all the info and more, but it does not say if it is an induction ( i highly doubt it) or a permanent magnet one ( most probably ).
AC induction motor = VFD
AC PM motor = AC servo drive
As always, those are guide lines, there are other types and mixes there.
11 Mar 2017 23:49 #89442 by denhen89
Thanks tommylight.

I found that .pdf also. i think on yesterday, but like you say there are no information about if its an induction or permanent magnet.
So i still dont know if i need an VFD or an AC servo drive. How its possible to find that out?
If i need an AC Servo drive, then for sure i could use some new "universal" servo drive, right? I was looking for an servo drive which "could" work (parameters like max. rpm), and found e.g. this website : cncmakers.com/cnc/controllers/Spindle_Mo...dle_Servo_Motor.html , where are a list which says the "GS2100Y" is for max. 12.000rpm, but unfortunately there are no pricelist and no more information, even not really on the .pdf (download file at bottom).
Its so difficult without experience. I dont know even know if its an Induction or permanent magnet motor. Have servo motors not constant torque from 1rpm to max. rpm ?

I took a look on the kW and torque curve of the Fanuc 3S-12000. The max. torque is constant until about 1.800rpm, then it drops drastically. The torque is rated as kgm, but due to my calculation (kgm to Nm) the torque is at 23.5 until 1.800 rpm and under 2 Nm at 12.000 rpm. Its not that important, but that should be an good combination for steel and aluminium or am i wrong?

Would be nice to figure out if i need an VFD or servo drive, and if its possible to do rigid tapping and use an ATC.
I will of course continue to look for information and try to figure it out by my own, but it would be great if someone could help me.

12 Mar 2017 00:06 #89444 by denhen89
Okay i have found something.
In the Fanuc Manual .PDF (first link on the google link you have send (tommylight)) at site 42 "3. CONFIGURATION AND ORDER SPECIFICATION DRAWING NUMBER" reads "AC spindle SERVO unit". So, am i right when its an AC Permanent magnet motor?
On the same site i found "Spindle orientation control circuit" as "OPTIONAL" not "BASIC". Is that the "Encoder" ?

Guys, i can just ask you thousand of questions and speculate, but i think i will never be 100% sure what i need :D.
12 Mar 2017 00:17 #89445 by tommylight
Do you have the motor? Can you actually touch ( well rotate by hand ) that motor?
If you can, then it is easy, find an LED light or multimeter or a torch light bulb, attach any of the items mentioned between two of the three motor wires and give it a spin.
If you get light or voltage, it is a PM motor, if not, it is induction.
12 Mar 2017 00:33 #89446 by denhen89
Thanks for the explanation how to test it, but unfortunately i dont have the motor right now. Im just a bit in hurry not only because i want to start to learn solidworks, but also because the price is really good compared to the prices i found on ebay for the same model and i will soon visit my family in germany so i could pick up the motor while traveling, because its almost on same road. Im coming from germany (living in Poland since about 4 years), so i could make a call every moment and buy it already.
I havent even start with the drawings and that would be my first part for CNC router machine, but that would be a good motivation and i also want buy all parts step by step.
12 Mar 2017 01:10 #89449 by PCW
As expected its just a standard induction motor


Note that the encoder has no commutation pins (needed for a permanent magnet motor)

Besides spindle motors are almost always induction motors since they allow wider speed ranges
because you can do efficient field weakening for high speeds
The following user(s) said Thank You: tommylight
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