Z Axis lifting during use

Mostly Printed CNC - MPCNC Troubleshooting
1

Hello,

i finished my MPCNC this year. X and Y work perfectly from the start, but my Z axis is lifting during milling.

I searched this forum for some troubleshooting ideas but so far nothing helped.

Here are some pictures showing the problem:

IMG_20210112_200850
IMG_20210112_2008504000×3000 1.38 MB
IMG_20210218_160543
IMG_20210218_1605434000×3000 1.19 MB

A 2mm deep carve carving in air after 1 hour and a 1 hour test without the spindle running(z0 was on the block)

Setup:
Arduino with CNC Shield and DRV8825 Drivers
Makita spindle
24v Led driver power supply
estlcam

My Troubleshooting so far:

  • Switching from a 12V Laptop Power Supply to a 24 V Supply
  • Testing a different DRV8825 stepper driver
  • Increasing the voltage for the stepper motor
  • Decreasing the max Z speed to a very very low speed
  • Re-Lubing the screw, tightening and loosening the spindlenut, tightening connector spinde/ stepper motor
  • running test without the spindle running
  • doing 100 holes in air without x and y movement - no z problem

On my To-Do list for testing are:

  • Connecting the cableshields to ground from the power supply - not much hope because z lifts even without the spindle running
  • maybe a new z-steppermotor or a bigger one
  • more jumpers on the cnc shield for microstepping

i really dont know what seems to be the problem. it might keeps missings steps that add up but i dont know.

here is a video of my mpcnc running. it looks pretty rough because you can see the steps. are your mpcncs running smoother? x and y are accurate tho. maybe its a software problem after all?

Hopefully someone has some more ideas for me to test and ill update you on the progress.

2

My first thought was estlcam has a clearance z lift option that could be throwing a wrench. But considering it is happening after some time it sounds like the z is loosing the origin some how. I would check the grub screws on the coupler from motor to rod. Maybe run the rod up and down by hand to see if it has any rough places or feels like it is catching.

3

Is the bit itself loose and moving up?

Do you hear it skip steps? It should sound like crunching gears.

4

Can you post the gcode from the air carve above? (2nd pic)

5

Hi @mineau23

of course you should make sure, that your bit doesn’t move up. If this is guaranteed, I recommend:

That makes a huge difference!
Ciao DJ

6

Thanks everyone.

  • the bit moving up cant be the problem - i test without the spindle running 20mm above the workplate

I changed all the jumpers to 1/32 microstepping and this was the result:

IMG_20210304_090433
IMG_20210304_0904333000×4000 1.63 MB

Everything worked perfect and z stayed at perfect 0, but in one of the last passes it got stuck and ruined the project :smiley: i dont know what caused this, maybe a cutout part got in the way.
Maybe 1800mm/min and 3mm z was a bit too much.

i might have solved the problem changing the microsteps.

@h0m3r2000 i tightend them 2 times already. the spindle moves when powered off really smooth. usually it slides down on its own after i cut power to the drivers
@jeffeb3 i dont think i ever heard a skipped step
@DJPicasso thanks for the tip, i ordered that driver just in case. might arrive in a month.

thanks for the tips!

1 Like
7

Hi @mineau23,
I do not work with wood but aluminium or carbon but I normally use 300 - 700 mm/min. In my opinion you should not work with more than 1000mm/min with arduino boards because of step losses.
Ciao DJ