I have built a 75x75cm MPCNC Burly and after drawing with a pen, cutting styrofoam and wood and learning a lot of things on the way I started to mill aluminum (for an estlcam “tastplatte”).
I had some problems with aluminum and had to tune in on the feeds and speeds and broke 3,175mm bit on the way
Now I am milling with a 6mm 1 flute aluminum drill bit from sorotec using estlcam and fusion 360
The z-axis is working fine and has big torque (I am using 2mm pitch on the lead screw), but when the drill is coming in contact with material (sideways, no z-axis movement in the g code), my z-axis is rotating and slowing moving UP!. I don’t think, that this is loosing steps, I can see the coupler slowly turning. When I try to move the z-axis by hand it is very hard.
Do you have any idea what the reason could be? Any defect part that could cause this? I think something broke or is loose (i checked the coupler, it’s not). Some aluminum chips landed on the arduino a few days ago, maybe a shortage?
Stepper motor
Coupler
Cables / interference
Stepper driver
arduino / arduino cnc shield
Any ideas where I should look into are very welcome!
hey mike,
thanks for your input, the spindle is fixed and does not move (at least not up and down, lateral rigidity is not perfect (yet)). I can see the coupler on the z-axis turn slowly, when there is no z-axis movement in the gcode (e.g. while planning a surface)
Hey jeffeb3,
the settings for the z-axis are okay I think: 800 steps per revolution, 2mm per revolution, 600mm/min max feed rate (so 5 revolutions per second max). This is working with no problems when moving the z-axis up and down “in the air”. the problem only occurs, when in contact with material and no z-movement is happening in the gcode.
I checked the coupler screws and one of them was not completely firm, I could turn 1/8th to 1/4 of a complete revolution. If that was the issue it would be very emberrassing for me I’ll give it another try and will report back!
Thanks!
I am kind of frustrated - I could not find the source of this issue. It only occurs when milling aluminum with a significant load. In wood or when milling aluminum with 0,1mm doc the issue is not present.
Milling with a feed rate of 1mm doc, 500mm/min and adaptive clearing or / troichoidal milling the issue immediately occurs after a few millimeters.
I went the long road: I rebuild my burly to primo and bought a new spindle (makita). So everything has changed other than:
You can take a marker and make a tick on the Z shaft on the top of the Z motor. This will help you see if the motor shaft is turning when it is slipping. If it is, then it is skipped steps (and I would be surprised). If it isn’t, then you have to just keep looking down the line until you find what isn’t sticking. I still suspect the coupler, so maybe make a mark on it so if it moves at all, the marks won’t line up anymore.
Milling like this is like a million little hammer blows. So even though everything is strong, it may move a very small amount with each little blow.
Thank you Jeffeb3! I added markers (tape) to the z-axis (stepper, coupler, leadscrew) and run a few more tests and I could identify the issue: The bit was slipping out of the collet - sorry, I feel kinda emberassed that I did not check that in the first place.
I am sure, that this was not the issue with the previous build from me (Burly) but since the symptoms were the same I thought the problems from my burly build persisted with the primo!!
After tightening the collet there is no more z-drop. Only my 30€ bit is broken I think, but that is fixable
The MPCNC is fantastic and it’s fantastic to find other people willing to help when thinks don’t work as expected.
Images:
Video Analysis of “accident” (z-axis movement wihtout z-change in gcode, adhesive tape on z-axis not moving)
I’ll give it another try and will report back!
