Y axis moves when it should not move

Mostly Printed CNC - MPCNC Troubleshooting
1

Hi guys,
I tried engraving some PCBs on my mpcnc today. But after a few minutes the Y axis starts to move when it should not move. Lines that should be only in X Direction start to drift of in Y Direction. The problem is not on the gcode (which is generated by pcb-gconde ulp in eagle) since the problem occurs on different locations on every try. I turned down the maximum speed all the way to 200 mm/min but nothing changed. My next thougt was that maybe the stepperdrivers overheat, switch of and the spindle drags the axis away from its path. I monitored the temperatures for a whole run and they never exceeded 30°C which i think should be fine.
Do you have any more ideas what could cause this problem?

Thanks,
Philipp

My setup:
eagle -> pcb-gcode ulp -> estlcam -> arduino with cnc shield and a4988 drivers (GBRL all in estlcam) -> mpcnc with 1 meter conduit (~73 cm working area) and makita rt0700 spindle

20200319_000421
20200319_0004213456×4608 2.84 MB

2

Step one is alway to check the grub screws on the pulleys.

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3

Hi Tom,
i checked the screws and they are all tight. When the motors are powered up there is no play in the axis (while the machine is idling).

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4

If the current is too high the motor driver could go into thermal shutdown and then it has no torque (intermittently). Try again (no spindle, just moving in air) and tug on the motor periodically to see if it still has torque after a while. Actually you don’t need to run a job for this, just let it idle with steppers engaged and see if it cuts out intermittently.

5

Since i already suspected a thermal shutdown i already tried pulling on the axis while idling. I did not notice any weakness. But i only did it once and not periodically. I will try that tomorrow.

6

I’m assuming you have your driver current set, right?

Have you completed other jobs with this cnc? The test crown, for example?

PCB milling should have almost no load. Is there anything that could be pulling on your gantry like a wiring harness or vac hose?

7

The current is set to 1A.
The crown was successful and also plotting with a drag knife works fine.
The only thing attached to the gantry is a drag chain, but it is not pulling on the gantry. I’ve tried removing the drag chain…but got same results.

8

Funky feedrates or rapids? If they are too far out of wack the machine just does what it wants.

9

Hi again,
sorry for not answering in a while. But i solved the problem. It was indeed a overheat problem. I replaced the fan in the housing with a much stronger one and now it works flawlessly.

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