This thread is old but I am having the same issue with the z axis. However, I don’t think it is reversing directions or a problem with the software.
I think that during cutting/plotting when the program tells the tool to raise up (positive z direction) for clearance to move to the next cut line, something is causing the threaded rod (or motor shaft) to get stuck making the motor stall/grind/whine. The pineapple coupler does not rotate when this happens and the threaded rod does not move, keeping the tool at the same height. Then, after moving to new x and y coordinates, it lowers the tool (negative z) to start the new line. But since it didn’t go up (positive z) earlier the tool gets pressed extra hard against the surface of the work piece. This is the ‘reversing’ I think Herman Meyer was referring to. Sometimes when raising before going to the next line it will increase in z some before freezing/grinding.
I have only used a sharpie or pen secured with zip ties at this point so when this mishap occurs the upward force from the table on the pen just pushes the pen higher up on the tool holder, slipping it through the zip ties holding it. If this were to happen while using a router bit held in a firmly mounted router, the force would surely break or bend the bit.
I’ve tried tightening my middle assembly and am going to try lubing the threaded rod as well. It appears straight and feeds through by hand fine.
So what could be causing this?
Also, for reference I have the old corners and rollers, but the new style middle assembly. My frame and middle rails seem pretty square. I haven’t had any other issues yet other than over tightening and cracking the roller locks and one of the feet during assembly, neither of which seem to be affecting performance. The workspace is 480mmx480mm with legs about 8″ tall.
Any ideas? I will post a video if I can catch the mishap in action.