OK, first principle of linear motion: the driving force must be applied parallel to the guide(s). In a screw driven system, driving force is coupled from the screw to whatever is being moved along the guide rail(s) by a nut mounted on the moving part. In a belt driven system, force from the motor is coupled to the moving part by the belt and clamp. In either system, the belt or screw must be kept parallel to the guide rail(s).
The Z axis screws appear to be arranged parallel to the Z axis guide rails. That's good, and as it should be, and for some reason, even first time printer builders seem to get this right.
The X axis belt is not parallel to the X axis guide rails. That's bad. That causes several problems. The belt tension will vary depending on the position of the extruder carriage. That means that in some positions, it may get so loose that the belt will slip on the drive pulley, resulting in layer shifting in the X axis (that's probably why the builder of this machine put a clothespin spring belt tensioner on the belt). In other extruder carriage positions, the belt may get too tight, causing the mechanism to bind, also resulting in layer shifting in the X axis. Even if the belt doesn't slip or the mechanism doesn't bind, since the drive angle varies with the position of the extruder carriage, all prints will be distorted. The amount of distortion will depend on their size and where the prints are located on the bed.
I can't see the Y axis belt because it's under the bed, but it's clear that the person who built the printer didn't understand how to use belts properly, so there's a good chance that the Y axis belt is also poorly positioned. The top part of the diagram below shows the common error in the Y axis. The bottom part of the diagram shows the correct position of the belt clamp so that the belt stays parallel to the Y axis guide rails.
![belt.jpg]( "belt.jpg")
Note that in the diagram, the bottom half of the belt loop doesn't connect to the bed. That half of the belt loop doesn't have to be parallel to the guide rail(s). The part that is clamped to the bed has to be kept parallel to the guide rail(s).
Look at the X axis belt in your printer. The top half of the belt loop that doesn't connect to the extruder carriage appears to be parallel to the guide rails, and the bottom half of the loop that does connect to the extruder carriage is not. That's exactly the opposite of how it should be. The side that's clamped to the extruder carriage must be parallel to the X axis guide rails, the other side doesn't need to be. I see a clothespin spring type tensioner on the belt. Those are always a bad idea in a precision mechanism and once the belt clamp is redesigned so the belt is kept parallel to the guide rails it will not be needed.
It looks like the Y axis motor is tilted, probably due to belt tension causing the too-thin motor mount plate to flex. That's another common problem that easy to fix.
The Z axis screws appear to be arranged parallel to the Z axis guide rails. That's good, and as it should be, and for some reason, even first time printer builders seem to get this right.
The X axis belt is not parallel to the X axis guide rails. That's bad. That causes several problems. The belt tension will vary depending on the position of the extruder carriage. That means that in some positions, it may get so loose that the belt will slip on the drive pulley, resulting in layer shifting in the X axis (that's probably why the builder of this machine put a clothespin spring belt tensioner on the belt). In other extruder carriage positions, the belt may get too tight, causing the mechanism to bind, also resulting in layer shifting in the X axis. Even if the belt doesn't slip or the mechanism doesn't bind, since the drive angle varies with the position of the extruder carriage, all prints will be distorted. The amount of distortion will depend on their size and where the prints are located on the bed.
I can't see the Y axis belt because it's under the bed, but it's clear that the person who built the printer didn't understand how to use belts properly, so there's a good chance that the Y axis belt is also poorly positioned. The top part of the diagram below shows the common error in the Y axis. The bottom part of the diagram shows the correct position of the belt clamp so that the belt stays parallel to the Y axis guide rails.
Note that in the diagram, the bottom half of the belt loop doesn't connect to the bed. That half of the belt loop doesn't have to be parallel to the guide rail(s). The part that is clamped to the bed has to be kept parallel to the guide rail(s).
Look at the X axis belt in your printer. The top half of the belt loop that doesn't connect to the extruder carriage appears to be parallel to the guide rails, and the bottom half of the loop that does connect to the extruder carriage is not. That's exactly the opposite of how it should be. The side that's clamped to the extruder carriage must be parallel to the X axis guide rails, the other side doesn't need to be. I see a clothespin spring type tensioner on the belt. Those are always a bad idea in a precision mechanism and once the belt clamp is redesigned so the belt is kept parallel to the guide rails it will not be needed.
It looks like the Y axis motor is tilted, probably due to belt tension causing the too-thin motor mount plate to flex. That's another common problem that easy to fix.