Ever had an AC servo fail ?

Milacron · May 2, 2011

I never have, but I've run across a screamin deal on an identical one (Bosch SE B04 size) to what I have on a Deckel mill, and tempted to buy it as a spare "just in case". And yet these things may be so reliable it may be silly to buy it really. Out of 200+ CNC machines that have passed thru here in the past decade I only recall one bad axis motor and it was a DC type.

So, have you ever had an AC axis motor fail and if so, why do you think it happened...coolant ingress, high hours, manufacturing defect...or ??

3t3d · May 2, 2011

Coolant ingress for one.
Fixed by replacing the bearings and baking it out.

I've seen one that must have been over current to the point that one of the magnets was demagnetized. You could tell that, by shorting the leads, and turning the shaft.
If the magnets were all fine, it will turn hard, but still smooth.
If one of the magnets is gone, it will Cog over.

And I have seen a motor that was burned up, windings melted, due to a drive fault.

Tonytn36 · May 2, 2011

Yup, they go bad. Sometimes coolant, sometimes it's just the windings. Usually high hours though.

Mebfab · May 2, 2011

Had one give up when new, but dont know if AC or DC

And before you ask, because you rightfully will. It was on an anilam

Ox · May 2, 2011

Red Cap - High hours.

Definately NOT coolant.

---------------

Think Snow Eh!
Ox

Horseheadman · May 2, 2011

Have had to replace 2 on my Lagun/Anilam mill...just considered them defective due to collant/chip contamination.

I though I had one go out on my X axis in my Hardinge Conquest lathe. Sent the motor out for repair and it came back no problem found. Installed it and still had servo error. Ended up trouble shooting the motor over the phone with the technician that sent it back and after isolating the motor from the chasis, the damn plug connector smoked. It had been shorting internally, but couldn't detect under load because of the case grounding. When we isolated the motor, the load went directly thru the connector and identified the problem.

cncbrit · May 2, 2011

Haas, 10 years, 3 ac servo drives, 2 X axis cables, 1 X axis servo motor. I would get it just to help with troubleshooting the cable/drive if you ever have a problem, Its also a nice spare to have when selling the machine.

Milacron · May 2, 2011

3t3d said:
I've seen one that must have been over current to the point that one of the magnets was demagnetized. You could tell that, by shorting the leads, and turning the shaft.
If the magnets were all fine, it will turn hard, but still smooth.
If one of the magnets is gone, it will Cog over.

That sounds like a DC servo, not an AC

Milacron · May 2, 2011

cncbrit said:
Haas, 10 years, 3 ac servo drives, 2 X axis cables, 1 X axis servo motor. I would get it just to help with troubleshooting the cable/drive if you ever have a problem, Its also a nice spare to have when selling the machine.

For my curiosity, what size Haas and what did the motors cost ?

cncbrit · May 2, 2011

Ha, VFOE, $1600 :angry:

, I was so pissed, I wrote on the box, Z axis servo motor alarms 219 226 and 105, bad encoder or brake, $1600 replacement value. Would have thought about fixing it but it is for my bread and butter machine, needed it back up and running ASAP.

3t3d · May 2, 2011

Milacron said:
That sounds like a DC servo, not an AC

I took the time to answer your question. Yet you question my veracity?
Try to explain that to the AC motor then...

motion guru · May 3, 2011

AC Servo's lock up the shaft tight when the leads are shorted - any motor with magnets will do that regardless of brush or brushless.

We use that to our advantage on some lathe carriages where we are peeling logs at 1100 sfm and getting near the core. If you get a drive fault, just short the motor leads across a set of resistors or your wood cutting lathe will become a metal cutting lathe and destroy your chucks in a heart beat.

Hitting the chucks with the knife when the core is spinning at 800+ rpm with 300 HP behind it and . . . :ack2:

Miguels244 · May 3, 2011

motion guru said:
AC Servo's lock up the shaft tight when the leads are shorted - any motor with magnets will do that regardless of brush or brushless.

We use that to our advantage on some lathe carriages where we are peeling logs at 1100 sfm and getting near the core. If you get a drive fault, just short the motor leads across a set of resistors or your wood cutting lathe will become a metal cutting lathe and destroy your chucks in a heart beat.

Hitting the chucks with the knife when the core is spinning at 800+ rpm with 300 HP behind it and . . .

What do you use for switching?

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