Need Help!- Spindle motor for a lathe

[lokii]

I am currently upgrading/converting my lathe to CNC, and I have to replace the spindle motor.
After reading a few threads on here, I've found two ways of achieving my goals, which is to have the spindle as another axis.

As far as I can understand this can be done by either using a separate servo motor alongside the spindle motor and switching the servo on & off as needed.

Or

I can get the same result by using an induction motor, with feedback, the same way as modern milling spindles work with an auto tool changer.

I know these are the two options I have to achieve what I want, but I don't know enough about electrics to actually do this.

Can some kind soul please help.

[lokii]

I found this thread Lathe Variable Spindle motor options? VFD? Servo? Stepper? DC? after I post this one so my apologies for creating a duplicate thread, so quoting the last post by Al the Man.

"Where you install encoders depends on what functions you want to have on the Spindle/C axis.
For just precise control of the spindle motor speed, you should have one on the motor to act as a digital tach." Yes I want precise control of the spindle speed.

"If you want to do threading and have CSF(probably a stupid question, CSF?) then the encoder should be on the final spindle shaft, especially if gear or belt change is used." Yes I want to do threading.

"If you want to have a true C axis and use Live tooling etc, then the best solution is a C axis positioning motor over and above the Spindle motor." Yes I want true C axis and use live tooling.

"If the spindle motor has an encoder and there is an encoder on the spindle shaft and the coupling is precise and you have a high quality servo motor controller then it is sometimes possible to achieve C axis control with only the spindle motor itself."

So with what info I now have, can I assume the following.

Spindle motor: AC induction with encoder on either the motor or shaft coming off the motor, but must be directly coupled to the motor shaft in some fashion.

Spindle: driven by spindle motor via belt, with encoder directly coupled to it.

Speed control: A VFD, will this provide precise speed control.

C axis: controlled by means of a high quality servo driver.

If I have got the above correct, I can achieve what I want using only one motor, and not having to have a separate servo motor to control C axis.
Or am I going to be better off doing all of the above and have a separate servo motor for C axis.

[Al_The_Man]

CSF = Constant Surface Feed, G96.
How and what you need to achieve all this depends on what controller you are using and what method it supports, if any.
Al.

[lokii]

Thanks Al.

Constant Surface Feed, don't believe I didn't get that one, how embarrassing.

For a controller I was looking at usbcnc. Unless you know of a more suitable one?

[Al_The_Man]

I know nothing about the CNCUSB but you need to check the options and the way they are implemented in order to set up a C axis and spindle etc.
They may not have the G96 option?
Al.

[lokii]

I just had a look to see if it supports G96, it doesn't. so I'll have to look for something more suitable that does support G96.

I don't suppose you know off hand, if Mach3 supports G96?

[Al_The_Man]

I believe it does, but I don't think it is via a spindle encoder?
Al.

[lokii]

I've just had a look at the Mach3 manual and I couldn't find any reference to G96, but I did find that Linuxcnc, EMC2 supports G96.

[Al_The_Man]

If this poster on the Mach forum is right it does?
Mach 3 turn constant sfm?
Al.

[lokii]

Absolutely bizarre, Mach3 clearly works and supports G96, but I cannot find it anywhere in the manual.

I think I'll just go along with that one.

I suppose the best thing to do is try both EMC2 & Mach3, and then decide which one I prefer.

Many thanks for you time Al, I really appreciate it.