I have recently acquired a 'CraftBot XL' 3D printer (sold by CraftUnique), which is a CoreXY 3D printer with linear rails. It is a second-hand purchase and the seller were a company that had several. This particular unit has an issue where sometimes during X-axis movement, the Y-axis would move as well. They replaced the stepper motors, but the problem persisted so they opted to sell the machine.
I have found a possible cause of this issue. When I tried to move the carriage around manually, I noticed a particular heavy resistance / "drag" on approx. 1/3rd to 1/2 of the X-axis motion, toward the left extent of the build space. The remainder of the X axis and the Y and Z-axes are completely free to move as they ought to.
The force required to move the carriage in the problematic part of the X-axis is (subjectively) quite large. Much much larger than any other movement. I believe that during some combined XY-manouevers (diagonal movement), this force is too large, causing the carriage to only move in the Y-axis, resulting in errant behavior (at best: layer shift, at worst: carriage getting stuck and the printer needing to be reset). The behavior arises during homing often, as the home position is in the problematic area. An additional reason that I think the X-axis force is too large is that, when this problem occurs and I ever so slightly help the carriage along the X-axis with my hand, the movement can complete without issue.
Steps I have undertaken to no avail yet:
- Re-tension belts, make sure they are of roughly equal tension all around
- Lubricate all axes with PTFE dry lube spray
- Disconnect belts to see if they are causing the issue (they aren't, with belts completely disconnected the problem is unchanged)
This is a diagram of the setup:
What else could be causing this? I don't hear any out of place noises like metal grinding.
The next thing I want to check is the squareness of the gantry. I think I know how to measure it, but I'm not sure how to adjust it if it's off. Any help there?