Need Help! - X/Y motors all of a sudden chattering/struggling under no load

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27 Aug 2023 23:53 #279121 by Sray69
Hey guys,
I have been running my CNC now for quite some time with no issues at all. The other day I started it up and when Homing it I noticed some high pitch whining sound coming from one/some of the motors. I was not sure what it was. I proceeded to manually move the machine around the table in all directions and at slow to rapid speeds and it seemed to work fine with no strange noises. So I setup my job and started cutting. Instantly the machine started chattering/vibrating quite violently. I immediately turned the speed all the way down to like 10% of the job speed (80 in/min). Even at 8 in/min it was chattering/vibrating, just not violently. I decided to mess around with feeds and speeds but nothing helped. At the time I was just cutting out a test piece from a 1/4 piece of plywood at a depth of .1 inches with the router at 16000 rpm and using a 1/8" straight bit (new). I have ran many jobs at much deeper depths and higher speeds with amazing success. This boggled me. While it was running I was feeling/observing/checking every single part/connection on the machine to see if I could find where it was coming from, but I couldn't. 

Because I was able to move the machine manually all around the table at any speed/direction with no sign of vibration or noise I starting to think it may be a bit/collet issue. I checked the runout on the first bit I used and it came to .007". This seemed a little high. So I chucked up another new bit and that one came to .006". Then I started to think that maybe it was the Dewalt collet. I was thinking that maybe I need to upgrade to a precision grade collet but wanted to be sure it was a collet issue. Today I decided to see if the machine would vibrate even with no load. So I ran a job with no wood or bit chucked. I was going to put slight pressure on the router as it was running to see if that caused the vibration. Well as soon as I started the job it started vibrating throughout the entire movement. There does not seem to be any direction that it does not vibrate. So that tells it is not the router at all. 

Next I disconnected the X/Y ballscrews from the gantry and Z axis assembly to see if maybe one/both are binding somehow. Once I disconnected I was able to easily slide the gantry and Z axis assembly back and forth. So that tells me it was not that, but I decided to run the job with them disconnected anyway just to see what is up. Well as expected the vibration started immediately. I can visibly see the ballscrews struggling/chattering (X/Y axes, not sure about Z though) accompanied by a whine that fluctuates. You can hear them struggling. 

This ONLY happens while running jobs, not while manually moving around. I have done nothing what-so-ever to the machine. It literally just happened overnight. I am not sure if there is something in my g-code that could be causing this? I am using the same software (Carbide Create Pro) I always use. I do not see anything visibly wrong/going on in my cabinet.

Here is a link to a video I took. You cannot really see much in the video. I was mainly trying to capture the sound it was making. At times it almost sounds like grinding. This was taken under no load at all and disconnected from the gantry and Z axis assembly. 

VIDEO

I have no idea even where to start. I am really hoping you guys can help and that there is a simple fix here. 

Thanks

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28 Aug 2023 00:21 #279123 by tommylight
Did you plug the machine into another power socket on the wall?
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28 Aug 2023 03:09 #279127 by Sray69
At first when I read it I thought to myself, no I didn't because it is on a dedicated 30A circuit and there is no other 30amp sockets, BUT I now remember that I had flipped the breaker in my shop panel after the last good run I had. I have never touched the breaker prior to that. And it has been running like it is now ever since I switched the breaker back on. It is an old breaker. Maybe there is a connection shorting either in the breaker or its connection in the panel. I will look into that tomorrow.

Question though. Why would it only cause this issue when running a job and not when manually moving the machine around?

Thanks for the suggestion! Fingers crossed that is it.

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28 Aug 2023 12:53 #279165 by tommylight
Spindle on, makes electrical noise, messes with signals.
Check grounding and shielding first.
Then check power supplies for noise/ripple.
I had a bad batch of power supplies, had to change all 3, they would cause so much noise the machine would shake and rattle sometimes, not always, just some times.
If you do not have an oscilloscope to check ripple, use a DVM set for AC voltage, anything above 0.2V = new power supply. Also, beware that some cheap DVM are not good for this.
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28 Aug 2023 18:41 #279194 by Sray69

Spindle on, makes electrical noise, messes with signals.

Same thing happens whether the spindle is on or off.

Check grounding and shielding first.

I will check the ground connections. Nothing has changed with shielding.

use a DVM set for AC voltage, anything above 0.2V = new power supply. 

Please excuse my ignorance here. What exactly do I check? The output power of the PS's? At the PS or the input at the drivers?

  

Thanks
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28 Aug 2023 20:57 #279212 by tommylight
Yes, and yes on the picture.

What exactly do I check? The output power of the PS's? At the PS or the input at the drivers?

Both, if the power supply is ok but at the stepper there is above 0.2V, means the noise is not from the supply but from the cabling.
Also measure between neutral and ground, should be under 2-3V AC. Probably even a bit more is OK, but that depends on other equipment in the shop/house/office.
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28 Aug 2023 21:00 #279213 by tommylight
Dang it, almost forgot, check the power supply when the machine is running, if the LED blinks = not enough current for the drives motors, so a bigger power supply or lower the motor current on motors that can handle it.
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28 Aug 2023 23:45 #279226 by smc.collins
I assume this machine uses stepper motors ? like a typical router setup. just X and Y or X Y and Z ? is it possible that someone backdrove the steppers while the machine was off ? usually when I have seen steppers misbehave in other non cnc applications, it is becuase the output driver has a problem and the motor gets stuck in 1 phase and then jitters violently. Backdriving a stepper could depending on the motor and drive output topography a induce a very high voltage and current that if improperly clamped COULD MAYBE burn the gate or short it to where it no longer cycles properly. That would cause jerking and other strang motion issues. Try this, put your multi meter on the motor pairs, usually A and B, put the meter in RMS mode and then check and see if the RMS voltages are significantly different, if they are, put the meter in duty cycle " probobly kiloherz range, and see if the frequency and duty cycle are different. Typically a stepper has a 50% duty cycle and that produces a relatively constant AVG voltage RMS. Just something to peek into
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29 Aug 2023 04:09 #279250 by Sray69

Both, if the power supply is ok but at the stepper there is above 0.2V, means the noise is not from the supply but from the cabling.

Thanks. That is helpful.

Also measure between neutral and ground, should be under 2-3V AC. Probably even a bit more is OK, but that depends on other equipment in the shop/house/office.

Where exactly should I be measuring this? And using the same settings on the DVM?

check the power supply when the machine is running, if the LED blinks = not enough current for the drives motors, so a bigger power supply or lower the motor current on motors that can handle it.

I assume the blinking LEDs would be on the drivers? Or on the PS? If the power supply is good then it should have enough power. I feel like I made sure of that when I purchased it. I am not sure what the motor current is set at currently. I thought I set it on the lower end when I set them up just to be safe. I will check that in the morning.

Thanks for your assistance!

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29 Aug 2023 04:30 #279254 by Sray69

I assume this machine uses stepper motors ? like a typical router setup. just X and Y or X Y and Z ?

Yes. Nema 24s for X/Y and Nema 23 for Z.

is it possible that someone backdrove the steppers while the machine was off ? usually when I have seen steppers misbehave in other non cnc applications, it is becuase the output driver has a problem and the motor gets stuck in 1 phase and then jitters violently. Backdriving a stepper could depending on the motor and drive output topography a induce a very high voltage and current that if improperly clamped COULD MAYBE burn the gate or short it to where it no longer cycles properly. That would cause jerking and other strang motion issues.

Not real sure I understand what backdriving the steppers means. I can say that I ran a successful job one day. Shut everything down as normal. I do recall shutting off the 30 amp breaker in my shop electrical sub-panel (which I had never done before). The next day flipped the breaker on and started the CNC up and when I tried to run a job that is when I noticed this issue. So I don't think I backdrove the steppers.

Try this, put your multi meter on the motor pairs, usually A and B, put the meter in RMS mode and then check and see if the RMS voltages are significantly different, if they are, put the meter in duty cycle " probobly kiloherz range, and see if the frequency and duty cycle are different. Typically a stepper has a 50% duty cycle and that produces a relatively constant AVG voltage RMS. Just something to peek into

Just so I understand correctly. I would first check A+/A- and then B+/B- and compare? I assume this would be done while the machine is running a job?
 

Thanks for your suggestions.
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