Problem- Mitsubishi CNC on lathe: alarm light flickers while threading

[HuFlungDung]

I have a Mitsubishi Meldas 50L controller retrofitted onto an older American Eagle slant bed CNC. This was done back in about 1996 or so.

Anyways, its working fine up til today. I was doing some coarse lead threading with 24mm lead and running about 200 rpm. So the carriage is moving right along but not as fast as it does in 100% rapid.

The thread cycle is about 30 passes. The single depth of the thread is .315" and I am cutting this in UHMW so it is easy going. Because it is a round thread, I am using G33. The thread is internal.

In the initial passes, it seemed okay but I thought I noticed the alarm LED flickering out of the corner of my eye once in a while. I'd then watch it and it wouldn't flicker at all.

After running through the full threading program half a dozen times, then the alarm LED would flicker on more consistently and I could see it easily now, but the machine did not stop threading at all, and no real alarm was set.

The alarm LED seemed to flicker on at the end of the cut, when the tool withdraws in X in a smooth continuous motion tied right in with the threading Z movement. Perhaps it was my imagination, but it seemed as though the larger the X withdrawal, the more pronounced the alarm LED flicker was. Even the green Ready LED seemed to flicker a bit, but the power to the machine itself seemed to be fine.

I watched the servo loads and it is difficult to see what is going on there in real time. But Z seemed to operate with 100% (on rapid) and the X seemed considerably less, although its movements are extremely brief.

So I suppose the carriage just comes to a dead stop at the end of Z and then X motion follows. There are likely some tight accel/decel going on in quick succession.

So should I worry? Like I said, no real alarm was set, and the threads came out without any problems.

[onthebumper]

Sounds like a strange problem. The alarm LED is usually driven by the machines PLC or ladder. The PLC may be programmed to turn on the LED when the machine Ready goes off from the Mits side. If you are also talking about the Ready LED on the Mitsubishi OP Panel then that one is driven by the Mitsubishi side. You may have a problem that is just starting and may progressively become worse.
Did you check the alarm page as the LED was blinking? Maybe you can get a better idea of what is happening with a description of a hard alarm.

[Captdave]

Just for kicks, try slowing the spindle speed down a touch and see if it still flickers, it may be running the maximum the servo can keep up with.

[HuFlungDung]

I did watch the alarm page as this was going on, and nothing appeared there. The LED's I am referring to are on the Mits operator panel which the retrofitter supplied. I didn't try looking at the digital display in the cabinet, I will try that.

I've got another more typical fine pitch threading job coming up soon, which has never given any problems so I'll look at what goes on then, too.