Fanuc 6MB - Spindle abruptly stops, feed continues, breakage ensues.

Hello all,

bear with me, I am new to CNC. Our shop has a Kuraki KBT 1105DX with Fanuc 6MB controls. We are having an issue where the the spindle will abruptly stop while cutting, but the feeding will continue. Obviously, this will tend to break things.

There are no alarms shown on the control screen. Operator says that the speed is otherwise well-controlled. I would have expected that if the controls saw the speed drop out, it would set an alarm and stop the feed, but maybe I'm being too optimistic.

Edited to Add: this is a DC spindle motor. I'm not sure what version of the spindle controller I'm working with, I haven't had a chance to open the cabinet yet.

Are there any obvious things I should troubleshoot first?

Any help would be appreciated.

Regards,

Ryan

How to proceed depends on the type of spindle control: the 6M has both analog spindle and binary spindle outputs. Also, the OEM should have implemented an interlock to prevent the feed from continuing when the spindle speed drops below a certain RPM

Quote:

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Originally Posted by memoryman

How to proceed depends on the type of spindle control: the 6M has both analog spindle and binary spindle outputs. Also, the OEM should have implemented an interlock to prevent the feed from continuing when the spindle speed drops below a certain RPM

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Thanks for the reply. As soon as I can get on the machine to troubleshoot, I'll reply back with more information. Electricians installing lights this morning, drew a short from somewhere and fried wires from here to kingdom-come. I believe we'll be in darkness for most of the day. :(

Hello moondawg,

Is your program feeding in Inches Per Minute (G94)? If you change that to Inches Per Rev (G95), your machine shouldn't feed anymore when the spindle cuts off. I realize this doesn't solve the core issue, but it may save on broken tooling until the issue is resolved.


Regards,

Paul

Thanks Paul, this is great feedback. I will share with our machine programmer.

As a further update, I have verified that the speed feedback is an analog Tachogenerator.

We have a controls guy that was here working on another machine and we chatted him up about this one. He suggested that the problem was either in the TG or the motor itself, as the spinde motor drive has been replaced (before I got here) but the problem persists.


Machine is currently apart due to a problem with the tool changer.

Our current next steps are:

1. Inspect and clean Tachogenerator, it appears this has never been done.
2. Inspect and clean motor brushes.
3. Monitor speed command signal to the drive and the output of the tachogenerator, make sure both signals are "clean" and stable.

Thanks to everyone who has viewed and contributed to this thread. I really appreciate it.

Ryan

That control has 3 methods of spindle speed control: analog or binary. The method used depends on the OEM's need.
Do you know the method used?
Also consider that the spindle stop signal may be causing your problem; even the M05 output.

Hi moondawg,

I've just the same problem... Did you solve it? How did you do it?

Thank you very much.