Dual Y gantry CNC router slowly getting out of square

[ryanjg11]

I repositioned my servo step and direction cables inside the cabinet tonight, to a safer area further away from the VFD. Then I re-ran the same program, observing in Clearpath MSP the Cnts of each servo before and after the program. Here are the new Cnts I'm seeing (before and after the same program is ran):

Result to the naked eye: upon completion and returning to 0,0, I can see the router bit is about 1/2" off in both Y and Z
Y Slave: +4,025 to +4,025 (0 difference)
Y Master: -3,805 to -5,515 (1,710 difference)
X: +299,390 to +297,999 (1,391 difference)
Z: -8,360 to to -8,598 (238 difference)

Next, I swapped out the unshielded VFD output cables running to my bulkhead connector and replaced it with a fully shielded VFD cable (the same as the outside run that goes in the cable track). Here are the results:

Result to the naked eye: same as before, about 1/2" off in both Y and Z
Y Slave: +28,712 to +28,713 (1 difference)
Y Master: -28,421 to -30,134 (1,713 difference)
X: +1,317 to -73 (1,390 difference)
Z: -1,228 to -1,467 (239 difference)

If the Cnts mismatch is resulting from noise, I guess I expected to see a bigger improvement here? It's a very small difference across the board. Curiously, my Y Slave servo continues to perform the best (with 0 or 1 Cnt difference after a 15-minute program) and yet it has the poorest routing path inside the cabinet (it runs closer to the VFD than the other cables).

[tblough]

Are your step and direction signals connected with shielded twisted pair wires to each motor driver? The step signal should be a single twisted pair with step and com lines and the direction cable should be the same.

[ryanjg11]

Are your step and direction signals connected with shielded twisted pair wires to each motor driver? The step signal should be a single twisted pair with step and com lines and the direction cable should be the same.

I'm just using unshielded industrial Cat5 cable for carrying all 8 wires in a single cable. Is that not recommended? I'm not sure if the step and direction pair are twisted, likely not since I wasn't aware of this requirement when making the cables.

[ShawnM]

Go buy a shielded CAT5 cable and do the same thing. Ground the shield at the common ground point in your cabinet. You do have a single ground point inside the cabinet, yes? Shielded wire is recommended and best practice for all signal wiring on the machine.

[ryanjg11]

Yep. I've read the shield should only be grounded at the controller GND?

[ryanjg11]

Also, Teknic's own cables aren't shielded?

Are we just talking about inside the cabinet here?

[ShawnM]

Also, Teknic's own cables aren't shielded?

Are we just talking about inside the cabinet here?

I edited my comment, shielded wire should be used everywhere on the machine. Signal wires, limit switch wiring, encoder wiring, VFD wiring. Noise in a system can have you chasing your tail for days, why not mitigate unwanted behavior from noise with proper shielded and grounded wire where you can?

[tblough]

Some say shielding should be grounded at one end to prevent ground loops. If you choose this method, I prefer grounding at the end the signals originate.

[ryanjg11]

Go buy a shielded CAT5 cable and do the same thing. Ground the shield at the common ground point in your cabinet. You do have a single ground point inside the cabinet, yes? Shielded wire is recommended and best practice for all signal wiring on the machine.

Shawn, can you explain how you grounded the shield of a CAT5 cable at the cabinet? I'm just trying to visualize how you did it. Ethernet doesn't include a 9th bare wire so I'm curious how one would do this in a clean manner.

[ShawnM]

Go buy a shielded CAT5 cable and do the same thing. Ground the shield at the common ground point in your cabinet. You do have a single ground point inside the cabinet, yes? Shielded wire is recommended and best practice for all signal wiring on the machine.

Shawn, can you explain how you grounded the shield of a CAT5 cable at the cabinet? I'm just trying to visualize how you did it. Ethernet doesn't include a 9th bare wire so I'm curious how one would do this in a clean manner.

Wait, what? I've never seen shielded CAT5 cable WITHOUT the foil braid and drain wire. I can post a pic if you like. I personally don't use CAT5 wire but I suggested it because that's what you were already using. It'll work very well for step and direction because of the twisted pairs.