One of the most asked about troubleshooting problems with a new X-carve is positioning errors. Almost all positioning errors are corrected by adjusting the various parts of the machine. Very few of the problems are actually due to failing components. The X-carve is a very flexible machine and so one answer cannot fit all situations. Each person will use their machine in a different way which makes it difficult to precisely quantify each adjustment.
Positioning errors are almost always due to some form of slipage. Either a pulley slips on a shaft, a belt slips on a pulley, a V-wheel slips on a Makerslide, or a stepper motor loses steps.
Another problem that can cause positioning errors is mechanical binding. Issues that can cause binding are V-wheels that are too tight, belts that are too tight, or binding with the Z axis screw.
Other causes are less obvious, a couple come to mind. The frame of the X-carve can "flex" during operation which may result in a cut that is outside of the expected tolerance. With a machine that is capable of sub-millmeter accuracies this can make a difference in a good or bad cut, especially if you are milling aluminum to tight tolerances.
Another type of error occurs if the spindle shaft is not tightly held in its motor mount resulting in "run-out" errors. Weak or loose collets can also cause this problem. Slightly bent mills and dull mills can cause similar behavior as well.
Eliminate mechanical problems:
1) Check the set screws in the pulleys. If you are not going to use Loctite - do this frequently.
2) Check the belt adjustment.
3) Check the V-wheel adjustment. (Do this with the least weight on an axis, ie remove the spindle/router to do the Z axis)
4) Check the frame for loose screws. (most people don't think about this one)
5) Check the frame to make sure it's square
Eliminate electrical problems: (loss of stepper motor steps, etc)
1) Check wiring for loose terminal screws
2) Check wiring for shorts between terminals (even a single strand of wire causes problems)
3) Check the current limit potentiometers (see below)
4) Eliminate electrical noise (shielded wires or low pass filters)
Check these threads for information on setting the current limits for your stepper motors. One method gives a precise method for setting the current value for those who have a multimeter and are comfortable with measuring voltages. The other method uses the performance of the machine as an indicator of the correct current limit range for your system.
Setting the current limits by voltage https://discuss.inventables.com/t/setting-the-stepper-motor-current-limit/14998
Here are some great videos including the second method for setting the current limits: https://discuss.inventables.com/t/x-carve-maintenance-troubleshooting-videos-add-your-own/13405