G76 on Fanuc 32i-Model A, Spindle Speed Override, Lathe

dodgin · Jul 11, 2018

On our Doosan lathe with Fanuc 32i we would like to be able to override the commanded spindle speed using the knob on the controller during a canned cycle, G76, as that's what is typical with the rest of the lathes in our shop. Is there any way to make this happen?

yardbird · Jul 11, 2018

Not that I know of? The macro program that runs the G76 cycle disables the spindle and feed overrides. I believe G31 G32 G91 are the same. The other machines are Fanuc controlled?

Brent

yardbird · Jul 11, 2018

I bet this feature is an extra paid option? Not a standard feature for a Doosan machine.

Brent

dodgin · Jul 11, 2018

Gotcha.

In our shop we've got (mostly) older Fanuc controllers...4T, 5T. It works with those.

Vancbiker · Jul 11, 2018

Disabling the spindle override is determined by the machine builder, not Fanuc on newer controls.

Adjusting the spindle speed during a threading cycle on older controls usually results in a slightly imperfect thread form due to synchronization errors between the Z servo and the spindle drive. The Z servo velocity is only updated once per spindle revolution. The amount of error depends on how quickly and how far the override is turned and the spindle's response speed to override input. Generally it is advised to not adjust the override during threading operations.

dodgin · Jul 12, 2018

Interesting.

Thanks guys.

sinha · Jul 15, 2018

Vancbiker said:
Disabling the spindle override is determined by the machine builder, not Fanuc on newer controls.

Adjusting the spindle speed during a threading cycle on older controls usually results in a slightly imperfect thread form due to synchronization errors between the Z servo and the spindle drive. The Z servo velocity is only updated once per spindle revolution. The amount of error depends on how quickly and how far the override is turned and the spindle's response speed to override input. Generally it is advised to not adjust the override during threading operations.

Yes. That is correct. A changed spindle speed might result in a shifted helix, hence the same rpm must be used, even if it is possible to change it. It is because of this reason that CSS is not used in threading.

rainman · Jul 16, 2018

I've run Okumas in the past that would "accept" CSS for threading, but what a mess it made of threads when it was used!

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