X, Y, and Z with Pro XXL

I purchased my Shapeoko Pro XXL about a year ago. Since this was my introduction into the world of CNC it has taken some time to understand how the machine should respond in certain situations. Although I still consider myself a novice, I have learned a lot in the past year, or so I thought.

Recently, out of the blue, my machine suddenly developed a hiccup in the XY movement. To be more specific, the first problem I noticed was that the right-side stepper motor developed a noticeable shimmy and started skipping at random times, but only as it returned to the homing position after a cut. Naturally, I thought it was due to excessive slack in the belt, so I adjusted it and re-squared the machine as you are supposed to.

Believing the issue had been properly addressed, it was business as usual for about a week. Then, all of a sudden, the studdering and skipping in the right side Y stepper reappeared without warning. However, the issue was no longer contained to just the right-side Y stepper motor. Like a virus, the issue returned with a vengeance and seemingly infected both the left side Y stepper and the X stepper motors. So, the only thing left to do was to order a tuneup kit, restretch new belts, and resquare the machine. Unfortunately, I still could not get rid of the skipping and shuddering in any of the motors.

After hours of reading through a lot of forum pages, I began to think that the GRBL settings could be the issue because I began using Lightburn around the same time to run a laser, but the only GRBL changes that need to be made when switching back and forth is $30 and $32. Everything else remained the same, and nothing I have read suggested that simply installing LightBurn would cause the GRBL settings to go haywire in CNC mode. So, I began digging into the meaning of each GRBL command and how it affects the machine’s operation.

Fast forward to this week, the issue has become increasingly worse. Almost every time I run a toolpath, the machine skips and doesn’t home correctly and will not return to zero without continually reinitializing, which is very annoying. Therefore, I decided to go through all the GRBL settings and test the steps for $100, 101, and 102. Upon testing the movements, I came up with the following results, which confused me on how I needed to proceed.

Let me begin by saying that I have the measurements in inches in CM (Carbide Motion) settings, but the GRBL shows 0 for $13, which is millimeters. I am not sure if that is an issue, but I have run it like that for a year with no issues, so I don’t know how it could be. Also, I will post my current GRBL settings at the end of this post. Today I decided to measure the XY stepper movement as it compares to the present GRBL settings.

First, I ran a test on the X-axis. Using the MDI line in CM, I entered G01X25F500 and pressed send. As I said in the beginning, I am still a novice at all this, but after extensive reading on the topic, I have come to understand that entering X25 in the G-Code should tell the machine to move 25 millimeters to the left, which is in the positive direction. The same holds true for entering Y25 as well as -25 for each direction. However, I get mixed results each time I enter the line of G-Code, and it is never the same result.

One time, the machine may act as expected and only move 25mm, while other times, it may move as much as 50.6mm in any direction. I cannot find any rhyme or reason as to why it would move as expected one time but not the next. It is unpredictable and now the machine will not reliably run a toolpath as it has started skipping steps in the middle of the toolpath, which ruins the project. If anyone has any suggestions, please let me know, I would really appreciate it. Thank you. My current GRBL and machine settings are posted below.

$$
$0=10
$1=255
$2=0
$3=5
$4=0
$5=0
$6=0
$10=1
$11=0.020
$12=0.010
$13=0
$20=0
$21=0
$22=1
$23=0
$24=200.000
$25=2000.000
$26=25
$27=3.000
$30=24000
$31=0
$32=0
$100=40.000
$101=40.000
$102=320.000
$110=10000.000
$111=10000.000
$112=1300.000
$120=500.000
$121=500.000
$122=100.000
$130=845.000
$131=845.000
$132=150.000
ok
N0G4P0.5
ok
$xG92.1G49G10L2P1X0Y0Z0G54G21G90
ok
ok
ok
ok
ok

When my xxl pro did this I found the problem to be in the wiring harness, specifically a connector was partially disconnecting based on movement. I would also check your rail lubrication…might need a little Mobile Vactra #2.

2 Likes

Thank you. However, I am embarrassed to say that wile I know the rails need to be lubed, I cannot find any literature that explains how or where to lubricate them.

See:

https://carbide3d.com/hub/docs/maintenance/

and

The other thing to check on a belt-drive machine is if both Y-axis motors are turning — power down and remove both Y-axis belts, then put a bit of tape on the pulleys (so as to more easily see their rotation), then power up, connect and try initializing — the Z-axis should initialize as normal, then the X- and Y-axis motors should begin turning, the X-axis should also initialize normally while the Y-axis motors will turn until they time out — do they turn evenly and in synch?

This is also a good chance to check the movement of the Y-axis on the linear rails.

Replace the belts swapping side-for-side and end-for-end.

Address any issues which are discovered.

Alright, I cleaned and lubricated the entire X-gantry, then I changed and replaced the X-axis with a new belt. I also disconnected the Y-axis belts, which will be replaced with new ones, and marked each Y-axis stepper before running the test you suggested. Upon powering back up and running a homing cycle, the X-axis homed correctly, and the Y steppers ran until they timed out. When the Y stepper wheels stopped, both lines I made on the drive wheel faces were aligned at similar angles, which leads me to believe they are running in step.

Now I will put it all back together and see what happens. Thanks.

I cleaned and lubed all the rails, inspected all the stepper connections, and then replaced and tuned all the drive belts. Next, I put the machine through its paces, and it does sound and move a lot smoother. Something I failed to mention before was that it sounded like the left drive belt had sand in it sometimes as the gantry moved forward from the home position. It no longer sounds like that. That maintenance seems to have cured the problem, for now, anyway.

However, I still don’t get the whole Gcode thing with the machine moving 56mm when it is told only to move 25mm but also able to zero itself correctly, most of the time. I obviously don’t understand what is supposed to be happening, so I will do more reading. Hopefully, it will also cut like new; I’ll find out tomorrow. Thank you.