prints leaning forward

[ken-zehnder 0]

Hi I love my Ultimaker but my prints seem to lean forward sometimes. I printed a test cube and then he UM robot with the same result...whats loose ?

[illuminarti 16]

Look at the pulleys attached to the front to back belts. Also the short belt on the motor in the back left corner, and the pulley on the motor. Make sure they are all very tight. You can use a permanent marker to mark the pulley and rods/shafts to make it easier to see any slipping.

Check that the belts are straight, not twisting as the head moves, and not catching on the frame (short belt).

[gr5 897]

Your issue is with the Y axis - motor is in back left corner.

If it leans forward in sudden steps occasionally it is usually a loose set-screw inside one of the 6 pulleys for that axis (yes six! check the two on the short belt the hardest of which to get to is on the motor shaft).

If it leans forward more gradually where every layer is missing just a few steps, then the problem can also be set-screw but more likely it is caused by a rubbing short-belt. While it is printing look to see if the short belt twists back and forth each time Y changes direction. If so it is rubbing. Move the pulley on the Y stepper closer to the motor - You have to take the corner cover off (just one screw), then remove the 4 screws that hold the Y stepper, lower the bed just below the Y motor so you can rest the Y motor on it and not pull too hard on the wires. Look at the distance from the pulley to the motor - you might have to slide it even closer - about 1/2mm from motor is usually good. Alternatively you could add 4 washers under the motor standoffs so the motor is another mm or so away from the wall. I'm not sure if the screws are long enough to handle another mm distance but probably will be okay.

Also look for black dust under the Y motor indicating a rubbing short belt.

Also push the head around with power off to see if Y axis seems to have higher resistance.