Spindle speed ~180% of commanded

[inthebay]

Hey all,

Working on a Fanuc 21-T Lathe. Spindle speed override is set to 100%. No gearbox in the machine, serial spindle control (no voltage offsets)

I command M3 S500, I get S873(ish) - no idea why. Checked through the parameters and Gear ratio of spindle to position code is set at 1:1 in parameter 3706

Any ideas here? I did check with a Tachometer and the spindle is indeed at 873rpm. I've called a G97 to cancel G96

Stumped!

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[oetkbyentc]

Does the machine have a dual wound spindle motor? If so check the winding contactor for proper operation
Also,
Look at G21.1 and .2 in the ladder.

both off indicates gear 1 parameter 3741
G21.1 on and G21.2 off indicates (should indicate) gear 2 parameter 3742
Check the above parameters as well as parameter 4020 the ensure they haven't been inadvertently changed.

Also try with the spindle override at 50%. Does the speed register at 250 or 440 rpm?

Look at the spindle information under the System area. Observe the spindle tuning and setting screens and see if anything there points to an issue.

[inthebay]

Does the machine have a dual wound spindle motor? If so check the winding contactor for proper operation
Also,
Look at G21.1 and .2 in the ladder.

both off indicates gear 1 parameter 3741
G21.1 on and G21.2 off indicates (should indicate) gear 2 parameter 3742
Check the above parameters as well as parameter 4020 the ensure they haven't been inadvertently changed.

Also try with the spindle override at 50%. Does the speed register at 250 or 440 rpm?

Look at the spindle information under the System area. Observe the spindle tuning and setting screens and see if anything there points to an issue.

Thanks for these leads, ill try and chase them all down when I get to the shop after work tonight.

There's no spindle speed override knob on the machine so I'm unsure how to force the SSO via code/parameter, but ill try. I'll also verify the offset is linear (or not)

[oetkbyentc]

No spindle override?
How did you determine the override is at 100%. If its not already set, you could try parameter 3106.5. It will display the spindle override value on the screen.
Does the control possibly use the Fanuc software operators panel for misc. Functions like spindle override?

[inthebay]

No spindle override?
How did you determine the override is at 100%. If its not already set, you could try parameter 3106.5. It will display the spindle override value on the screen.
Does the control possibly use the Fanuc software operators panel for misc. Functions like spindle override?

I forced the spindle override to be displayed via a parameter to verify. I cant remember which one it was right off the top of my head, but thats how I checked.

There is no spindle override in the operator panel as far as I can tell.

[inthebay]

Parameter #3734 is spindle speed max, I had dropped it from 7250 to 4500 (the max of the chuck)
returning it fixed this issue. I'm guessing that its multiplying by a gear ratio somewhere that is throwing the speed way off.

[inthebay]

The curious thing now is figuring out where that gear ratio (or otherwise) is coming in and trying to fix it. I did notice that #3111 OPS was set to 0, meaning that it was displaying spindle motor speed instead of spindle speed, so I flipped that to a 1, but nevertheless the spindle still goes above the 4500rpm max that I'd like to set. Any ideas folks?

[oetkbyentc]

The spindle speeds are calculated from the value set for the maximum spindle motor speed and the value set for the maximum spindle speed for the selected gear.
So if you have a 1:1 motor/spindle ratio and you want to clamp the speed to 4500 set that value to both the maximum spindle motor speed and the maximum spindle speed.
I cant find parameter 3734 listed so I'm not sure what it is doing.

In my experience with serial spindles;
parameter 4020 is maximum spindle motor speed
parameter 3741 thru 3744 are maximum spindle speeds for gear 1 to 4.

Im also assuming since you said "limit the speed" that you will not be over speeding the spindle motor or spindle.

If you have other than a 1:1 ratio or multiple gears you would need to do some math for the correct numbers. But the max speed for all ranges would be lowered as the spindle motor portion is common to all ranges.