⬢Loosen the tensioning screw on the backside of the x-end-motor part. No need to remove the screw.
The tensioning mechanism may be a bit different on earlier MK3/MK3S printers. Although this guide is intended for MK3S+, it is also applicable to the earlier ones if you are aware of the difference.
⬢Release two M3 screws from the X-axis motor. No need to remove them from the plastic part.
⬢Rotate the X-axis motor as indicated towards the frame. And slightly tighten the upper screws to fix the position of the motor. It's just temporary.
⬢Pull out both ends of the X-axis belt and remove the entire belt from the printer.
⬢Manually rotate both threaded rods some more until the X-axis comes out of the rods.
⬢Carefully place the X-axis next to the printer as can be seen in the picture.
⬢Hold the x-end-motor (left printed part) with your hand and pull out the x-end-idler (right printed part) with your other hand.
Clearances in printed parts may vary slightly. In some cases, removing the part may be difficult. It may be necessary to use somewhat more force. But be careful not to get hurt or damage the cables!
⬢Make sure the X-axis motor is on the left and facing up.
⬢Gently slide one bearing onto the rod further away. Do not try to slide the bearing onto the rod tilted. Do not use excessive force!
⬢Carefully slide the two other bearings onto the rod closer to you. Same here, do not use too much force and not tilt the rod vs. bearing!
⬢Place both smooth rods into the channels in the extruder x-carriage. This is to make 100% sure cables are guided correctly.
⬢Slide the X-end-idler back onto the smooth rods. You may need to use a lot of force, but yet be careful. Do not use a hammer, F clamp or a similar tool. Keep the part perpendicular to the rods during insertion.
⬢Make sure that both trapezoidal (plastic) nuts are pointing towards you.
⬢Place the X-axis assembly with the black nuts pointing up onto the tops of the Z-axis threaded rods.
⬢Once again make sure that:
⬢The extruder cable bundle is above the lower smooth rod.
⬢The hotend cables are below the lower smooth rod.
⬢Turn the threaded rods simultaneously counter-clockwise to move the Z-axis a little lower.
⬢Leave a gap of approximately 1 cm (1/2") between the X-axis and the frame.
⬢Gently insert both smooth rods through the bearings inside the X-axis all the way down into printed parts. Do not apply too much force and do not tilt the rods!
Place the extruder onto the bearings and align the bearings as seen in the picture. The top couple must fit perfectly. The exact position of the lower one doesn't matter for now.
⬢Turn all three bearings so that the markings are facing exactly backward.
⬢Tighten the zip ties up and cut the remaining parts off.
⬢Make sure the lower bearing fits properly in the plastic part.
⬢Using the right hand rotate the motor to its original position and hold it there (tension is applied to the belt).
⬢Using two fingers on your left hand push the belt together. Very little force should be needed for bending the belt, BUT the belt shouldn't be bent by its own weight before being pressed with your fingers - it must be straight.
If you are struggling to rotate the motor back into position, the belt tension is too high.
⬢Depending on the belt being under or overstretched, adjust the position of the belt in the X-carriage.
⬢When done, rotate the motor to its original position and tighten the M3 screws up again.
⬢Use the technique described below to test if the belt is stretched properly.
⬢Use pliers to hold the X-axis motor shaft.
⬢Move the extruder towards the X-axis motor. Don't use excessive force.
⬢If the belt is stretched properly, you should feel some resistance and the extruder won't move at all. If the belt is too loose, it will deform (create a "wave") and jump over the teeth on the pulley.
Belt too loose? Return to the previous step and repeat all steps until now. You have to rotate the motor and retighten the belt in the X-carriage. Shortening the belt length by moving one or two teeth outside X-carriage should be enough.
In this step, we will finish adjusting the belt tension. Please read the instructions first, your belt might have proper tension set already, then there is no need for additional screw adjustment.
⬢First, slightly release all the screws holding the motor. Otherwise, the "tensioner" won't work (the motor must be able to move).
⬢Using ball-end Allen key start tightening the screw on the rear side of the X-end-motor, but after each turn or two check the tension in the belt.
⬢For the optimal performance, the belt must feel stiff if you pinch it with your fingers. Move the extruder all the way to the X-end-idler and try the belt tension in the middle of the X-axis.
⬢When you achieve an optimal tension, please tighten the screws up again.
In case you are experiencing X-axis failures during calibration or skipped layers in the X direction, adjust this screw accordingly. Tightening the screw stretches the belt. Releasing the screw has the opposite effect. And don't forget to release the screws on the motor first :)
Before proceeding further, make sure the nylon filament does not fall out of the extruder. If it does, please use the instructions in the MK3S+ assembly manual to install it.
⬢Place the x-carriage-back onto the extruder. Use all four M3x10 screws and tighten the X-carriage-back up.
DO NOT tighten the screws using unreasonable force!! Make sure you don't squeeze the bearings between the printed parts unevenly.
⬢Before you start printing, you need to calibrate the Z-axis.
⬢Remove the cloth from the heatbed.
⬢Place the steelsheet back on the heatbed.
⬢Turn the printer ON.
⬢On the printer screen navigate to Calibration -> Calibrate Z and following the instructions on the display.
⬢Great job! It was not so easy, but you have just successfully replaced the X-axis bearings!
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