Bottom line up front - We have a problem with electrical Noise in the CNC Router. Noise doesn’t come just from the spindle and steppers on the router, but from other equipment in Hive13 as well.
As CNC Warden I’m calling for volunteers to join an electrical noise mitigation project for the CNC Router. We need CNC users, wannabe CNC users and electronics makers for planning and hands on help. We can break this down into sub-tasks and share the work. See the outline below.
When: Planning to start in mid-January. We need to sketch the improvements, buy parts and plan the install. The dollar cost is probably low. Perhaps under $400.
Back Ground: Most everyone who has used our big CNC Router has encountered a random e-stop. It happens so often, restarting after an e-stop is almost standard procedure. Groan. E-stops are bad, but the noise level is so high that occasionally the hall effect end stops are ignored.
The Solution: Suspecting noise, I asked Lorin for advice, which resulted in this set of steps to mitigate noise in the CPU:
Assure star grounding for all components of the CNC Router. Create a grounding buss bar connected to a chassis ground for the control module on the wall. Follow best practices for independently grounding the steppers, spindle and chassis to the ground buss. This buss can be a metal bar with tapped holes, ring terminals and 12 ga wire.
Shorten and repair or replace all external signal and driver wiring with shielded twisted double pair wiring. Attach shields to ground for all external signal wiring. Because current wiring shields are not continuous and do not connect to ground they are antennas. Add ferrite loops to signal lines to damp out spikes.
Add a separate power supply for logic level voltages 5v & 12v. Stop feeding power from USB to logic boards. Use the separate power supply. USB is not well shielded.
Shield the microprocessors in individual metal boxes.
Low priority – Check/filter RF noise from spindle motor. Add filters on stepper motors. This is probably redundant to stepper drivers.
None of this is planned out in any detail though we can sub divide the tasks as follows to make each job easier for a team.
This isn’t guaranteed to solve all problems, but the noise we tracked on the oscilloscope is guaranteed to cause intermittent problems. We saw a 1 to 12.5 signal to noise ratio on one e-stop lead. Wow.
Steps 1 and 2 should have big payoff. Steps 3 and 4 are further protection.
One obvious team division is inside and outside of the plastic shield on the wall.
The controller team(s) will gather parts, make the bus, power supply mounts and shield boxes in advance, then do a get’er done Saturday change over to minimize down time.
The external wiring team would assure shielded/grounded cables on the table. Add grounding to the spindle, steppers and carriage so they are all electrically neutral to one another. The external wiring can be done over time before and after the controller changes.
Let’s discuss it here, form up teams and make this happen.
Have a Merry Christmas, See you all in January.