What happens when you crash a ball screw?

[aquanub]

Hey all,

I recently got a pendant setup on my machine and fat fingered a button... ended up running the PR to the limit of the X axis.

The motor kept turning and I made some awful noises. I rehomed the machine and all seemed well.

Can someone break down what is exactly happening when the ball nut is at the end of the ballscrew but the motor keeps turning? Knowing the structure of how the ball screw is assembled... everything seems very rigid.

What is exactly skipping? The driver motor in the coupling? I assume since everything resumed properly that things are ok, but I'm curious to know what exactly was "giving" when bottomed out?

Thanks & happy holidays!

[squid509]

the magnetic filed in the motor is slipping

the stepper motor stator (the part that dose not move) generates a moving magnetic field that the rotor try to follow. if the rotor is jammed is some way the magnetic field keeps moving causing the rotor to jerk around while trying to keep up

www.youtube.com/watch?v=eyqwLiowZiU

[rcferguson]

No harm, no foul. Just the motor vibrating as it tries to turn but can't. I suppose if it went on for a long time it might overheat and damage the motor, but I'd think it would have to go on for many minutes to actually hurt anything.

[Derek the Admin]

Squid gave a great explanation. It sounds bad when it happens, but rarely causes any problems.

[squid509]

Dec 25, 2019 2:06:28 GMT Derek the Admin said:

Squid gave a great explanation. It sounds bad when it happens, but rarely causes any problems.

it not good for the motor it cause current and heat spikes, and these machines have no position tracking other than counting the number of steps it made. if the machine starts to skip steps when cutting a project it will come out ruined 

[Bruce]

Yeah, if you grind the motors you will want to re-home the machine (or re-set the workpiece zero if you don't use limit switches.)

[Derek the Admin]

Dec 26, 2019 22:53:54 GMT squid509 said:

Dec 25, 2019 2:06:28 GMT Derek the Admin said:

Squid gave a great explanation. It sounds bad when it happens, but rarely causes any problems.

it not good for the motor it cause current and heat spikes, and these machines have no position tracking other than counting the number of steps it made. if the machine starts to skip steps when cutting a project it will come out ruined 

I agree. I'm talking long term problems though. For sure, in the immediate term, one should rehome if they run into the end of travel.