Sporadic X axis shifting

Here is some things I would check.

Check for binding.

This could happen if one of your axis rods is bent or not parallel ( this would also give you ovals rather then circles), as long as your carriages on the y axis aren't damaged then the x axis should be parallel but your y axis may have jumped a tooth and that can cause binding. So one way to  check for that is to bring the print head all the way forward and then count the teeth between the carriage and the gear each side the should be the same if not you have jumped a tooth. If you have jumped a tooth you will need to loosen the bearing holder push it forward for some slack  tighten it up and then make it jump the needed number of teeth. then re-loosen the bearing holder and let it return to the correct tension.

Check to see if your tensions for the axis are correct if they are loose that can allow you to jump a tooth. you can do this by loosening the bearing holders on each side near the front push them slightly forward and then allow them to spring back and then retighten. if your belt has loosened due to wear this will tighten them back up.

Check that your bearing holders are not cracked

Check to make sure you filament isn't binding the print head. if you are using a spool holder to much resistance can cause you to jump a tooth.

Anyway that's what I would check. maybe some of the others that have been doing this longer then me may have some other advice?

Actually, I think it was dual issue....and neither of those were it.

First, I replaced the grease/lubricant with some very nice and slick grease/lubricant. This seems to have helped tremendously.

Next, I went back and replaced the wiring harness for the x axis stepper motor. I cut the wires about 2" from the connectors and replaced the wiring with some 16 gauge wire I had sitting around. It's quite a bit thicker than the current wires, but it seems to be working well at the moment. We will see when this print finishes in a few hours.

Either way, I suspected the wiring was the problem. It wasn't binding on the sides or anything.

On my Davinci 1, I've had quite a few problems... most of them traced back to cable-tie pinch points that pull out or even bend connectors. this time I think those ties actually broke a connection inside a wire.

My X axis stepper started "randomly" jumping or reversing direction in the middle of move commands today. It sounded like sporadic loud angry grinding and at first I thought the motor itself was bad; but that was when the moves were all short ones. After reading the above comments, I tried holding/wiggling the connector while sending it individual longer "move" commands. Holding the connector seemed to affect the success chance of a command, so it appeared to be the connector. Then I noticed that each time it messed up or changed from working to not working, I had just brushed against that wire bundle, *above* the cable tie. I looked closer and the wires were severely creased just above the tie... (visible/reachable through the right-side vent aperture that looks like it should be a handle) I tried lightly flexing the wires in the general area of the crease (while machine was at rest) and many times heard the motor click just at the moment I was moving the wire as if being disconnected and reconnected while powered up. I had no way to definitively test the wires in place, so I chopped all 4 that went to the motor, just above/before the crease and spliced in a few inches of some (stranded, unlabeled, slightly thicker) wire I had laying around.

Before the splice I couldn't get it to behave for more than a few seconds at a time. As I type this I'm about one hour into what should be an 8 hour print (knock wood).

-I should mention in case it isn't obvious, that I'm Perma-Noob and not classroom compatible. My comments are based on observation more than prior knowledge.

I am, however, (just barely) smart enough to turn the printer off before cutting/splicing/soldering the wires