Fanuc AC Spindle and DC servos with geckos

Wonderful! Thank you! Makes me wonder can I use a normal VFD and still do Rigid Taping? Or do I need a CNC type drive like the Fanuc. Seems to me this can be done a lot more cost effectively with a different brand VFD. Thank you for your help thus far!

sgsracing wrote:

Wonderful! Thank you! Makes me wonder can I use a normal VFD and still do Rigid Taping? Or do I need a CNC type drive like the Fanuc. Seems to me this can be done a lot more cost effectively with a different brand VFD. Thank you for your help thus far!

You need a spindle encoder with index signal to do rigid tapping. The spindle drive is not terribly
important, although having an analog speed control is good as it allows the spindle to be more
gently slowed during the reverse. I have a Bridgeport with typical AC motor and a plain
VFD. I did put in a filter HAL component to slow down the speed change, and it works
fine. Adding the spindle encoder to the Bridgeport head was the toughest part of the job.

Jon

BigJohnT wrote:

I use an Automation Direct GS2 VFD on my BP with and encoder and the original AC motor to rigid tap. In my case the spindle is kwik switch so it was dead easy to add the encoder with no drawbar in the way. LinuxCNC has a GS2 component that uses modbus to control the VFD.

JT

Now we are talking! I had never considered keeping my old 5HP Ac motor and just adding an encoder ( and a VFD Provided I have an inverter duty motor..). I may still upgrade but knowing its an option to keep it is great! I have read about the GS2 component. in Linuxcnc but it didnt resonate with me! Now I will pay a little more attention as I know what it's about! If I dont use the GS2 component, and I use a AC Servo / Driver that has 0-10v analog where do I set that up in Linuxcnc? This is all wonderful stuff its all starting to come together now! Thank you all!

sgsracing wrote:

and a VFD Provided I have an inverter duty motor..).

You probably need the VFD, as it can make a more gradual reverse. I had to slow
donmw the reversing using a HAL component so the Z axis could keep up.

Don't worry about the "inverter duty" thing. I've been running stock motors on
my Bridgeport and lathe for years with VFDs. They ARE, however, dual-voltage
motors, rated for 240 or 480 V. So, they may have slightly heavier insulation
than would be found on a 240 V only motor.

Jon

Great! So If Im getting this all, I can:
- do rigid taping with my existing motor (inverter duty preferred but not mandatory) as long as I add an encoder.
-I can use a GS2 VFD and still be able to reverse the motor.

What would be the difference then to having a "AC Servo" vs a normal motor with VFD. What would be the benefits of using a servo. I get that keeping what I have has a huge cost benefit. but am I loosing performance? Thanks again for all the help its clearing things up BIG TIME!

sgsracing wrote:

Great! So If Im getting this all, I can:
- do rigid taping with my existing motor (inverter duty preferred but not mandatory) as long as I add an encoder.
-I can use a GS2 VFD and still be able to reverse the motor.

What would be the difference then to having a "AC Servo" vs a normal motor with VFD. What would be the benefits of using a servo. I get that keeping what I have has a huge cost benefit. but am I loosing performance? Thanks again for all the help its clearing things up BIG TIME!

The only real advantage to a servo spindle is it can lock to a particular position for
tool changes and to be used as a C axis. This is hot stuff on lathes for live tooling,
but has limited need on a mill. Some machines with CAT and BT tooling need
the spindle oriented pretty accurately for the spindle's drive dogs to engage
the toolholder's slots. Older machines had a sensor and a shot pin that
would do this, newer machines do it all with the spindle servo.

SOME servo drives may have a wider torque range without gear changes, but that
is basically just a higher HP motor than is needed at high speed, to guarantee
you have sufficient torque for low-speed work. That allows them to maybe
only have a 2-speed gearbox instead of multiple speeds.

Jon

Since LinuxCNC "gears" the axis motion to the spindle rotation via the encoder
feedback, I dont think much is gained with a AC servo on the spindle vs a VFD/induction motor.

Some exceptions might be applications where quick spindle orientation/positioning is
needed, and maybe for tapping blind holes where the AC servos faster reversing would help.