Rotacy CNC: That damn earthing again

Project history

  1. Previous project: TravelCNC
  2. previous step: Problem with optical input switches
  3. current posting
  4. next step
  5. Next project: designing a chain link tool library

When I assembled my newest DIY CNC mill on a piece of wooden OSB board... what could you possibly forget?
Wood is not conductive.

Everyhing is build super clean.
Crimped using the proper tools.
Signal power and signal ground distributed using proper DIN rail blocks.
Stepper drivers stronger then the actual power supply, steppers and forces needed.
Strangely enough I machined an entire part in perfect finish for a week before any issues showed up.
Then the A axis stepper starting moving on it's own and jittering. But only it it had already moved before. Not related to the spindle running or not.

Problem 1: wrong power supply

I had way too much power provided to my stepper drivers.
48V supply because the drivers where advertises as 8-50V input voltage.
Actually however where 8-42V with 50V being the absolute maximum rating.
The dealer overstated the capabilities of the driver.

Problem 2: Earthing

This did not solve my problem.
It needed a borrowed oscilloscope to figure out that I simply forgot to connect my giant A-axis gear box, sitting on the OSB base-plate to PE.
The power supplies (not the spindle) for the strong steppers seem to radiate a ton of EMI into the huge metal block that is the A axis. Static buildup from the gears inside and from machining plastic for days on end surely did not help either.
Since the power flowing from the motor to the motor driver caused the "work" LED on the driver to blink, I searched for hours where the supposed stray inputs to the driver came from. Not realizing that this came from the output of the drivers and not the inputs.

I had the same issues already with my Chinese 6040 CNC (all Aluminium but designed with no regard to earthing large metal parts and thus the steppers they connect to).
Seems I had to learn that lesson again.

Parts used

Keine Kommentare: