The motors on the Shapeoko are what’s known as “open loop”, that is, the controller does not know if the motor turned when commanded or whether the relevant axis moved the requested distance. Stepper motors move a known angle (1.8 degrees in this case) per step and the controls exploit this.
When the machine first powers up it finds the home position by moving until it trips the switches at one end of the travel of each axis. This allows the machine to set an internal zero point for each axis and it then simply remembers how many steps it has requested up or down that axis to “know” where it is.
If something happens, a pulley slips or the motor is unable to step when requested, there’s no way for the controller to know this as there is no feedback system.
So once your machine has slipped off track, be that from a loose pulley, loose belt or simply too much cutting force, it’s going to be stuck over there until you re-initialise the machine.
Thank you for the great feedback! The pictures were rotated 90degrees on accident. The shift has been consistent in the x-axis (I can’t tell you if it’s always positive or negative shift however).
Thank you for your help, however I am going to admit I really don’t understand your advise. Are you able to please re-phrase in noobie terms? I appreciate it! I love learning about this machine, and I found I learn more from making errors than perfect productions.
If this is the case, then everything after the ‘slip’ would be off as well. This is not the case. It will cut one portion off track, then jump back on track right after. Then when it drops down to the next layer, it jumps off at the same exact point (then back on…rinse & repeat).
This is why I was wondering if the problem could be digital rather than mechanical?
My guess is a semi-loose setscrew on the X axis motor pulley.
It is not impossible that the pulley slips on the shaft in one direction (say, the setscrew is not quite pressed hard enough enough the motor shaft flat, so it slips), then it “catches” the shaft’s flat again, then the cutting direction changes and it will slip & catch once in the other direction…ending up where it started.
I agree it sounds unlikely, but I would still triple check the two setscrews on the X motor pulley, no harm in doing that anyway at least to rule out this hypothesis.
Will is basically suggesting you make the “trench” for your cut wider so that the endmill isn’t tight within the slot when it is cutting. It means it will cut with a smaller part of the tools radius, rather than about half of its radius.
That said, I’ve never had problems cutting exactly like you are doing.
I would say that about 90% of all issues with unexpected behavior when cutting are mechanical, especially with new users and machines. As @Julien and myself have said, please check the set screws on the X motor pulley. It is very likely the issue and if it isn’t you will rule out that possibility by checking…
My experience aligns with this. If you’ve not seen the hint already, taking a marker pen and drawing a line across the face of the pulley and the motor shaft is a great way to tell if it’s slipping on the set-screws.
John,
Guarantee that this your set screws on the pulleys. I documented the issue here that is the exact same as yours:
This is the full solve with parts you need to purchase (it’s only a few $).
This is a frustratingly simple fix. It’s a bad experience for a new user trying to learn a machine and track an issue like this. You get all this advice on how troubleshoot it and misdirection about material forces, speeds and feeds, and slotting. The short story: it’s a design flaw that Carbide3D could resolve.
I’m at a loss on how to get the Carbide3D team to implement straight out of the factory. It’s a near zero cost solution for them, switch out current inadequate grub screws with better cap screws and removable thread lock. I’ve tried escalating here and emailed support. I’ll try again emailing support.
It’s not so much the set screws, lots of other machines use these successfully, it’s the lack of threadlock on those set screws allowing them to vibrate loose. There’s no shortage of holding force when they’re done up properly.
Using larger head steel bolts in these small thread aluminium pulleys to get more torque on the screw would likely move the problem to people stripping the threads out of the aluminium pulleys.
I’ve emailed about this long ago and continue to see this problem in the forums. The set screws used on the pulleys are inadequate and often slip, especially for new users. I documented a simple fix here: Pulley set screws - XXL
This is a solve that would cost Carbide3D near zero and prevent frustrating new user experiences. In the forums they get misdirection about material forces, speeds and feeds, and slotting. The short story: it’s a design flaw that Carbide3D could resolve. Shapeoko XXL - final pass is stretched or offset Shifting off track
Looking through the posts and replies, dozens of people have had this problem. How can I help you champion a change to this simple issue that causes a lot of grief and ruined projects, especially for your newest users?
It would be amazing if they proactively sent every owner a pack of 8 M3x8MM cap head screws and small tube of removable thread locker. That would be Customer Obsession!
So, as an update. I have been trying to tighten the x-axis belt. Unfortunately, I feel I am getting the belt as tight as possible, but it is not solving the issue. My speeds/feeds are slowed way down as well. I am lost for answers and getting frustrated! Is there another way to tighten the belt other than wrapping it through the little bracket and tightening the set screw?
Please post a file which causes this problem, or send it in to support@carbide3d.com — include the generated G-Code and step-by-step notes on how you are securing your stock and setting zero to it and managing all tool changes and we will do our best to look into this with you.
Thank you so much for the explanation. I definitely have been looking at the wrong location to tighten the belt.
Question: Is there a proper way to access this piece? I can probably take things apart until I reach it, however this is definitely not the desired approach.
@WillAdams or someone with a Pro will have to chime in here. I have a Shapeoko 3 so I don’t know exactly how the Pro is built. I imagine there is an angle at which you can access the set screws without disassembling it. You may have to anyway in order to verify that one of the screws is on the flat side of the shaft.
