Maintenance, Mods and Tips'n'Tricks - Prusa i3

[old man emu]

Access is the biggest hurdle to overcome when you want to tension the X-axis belt. The ends of the belt are hidden behind the plate which holds the bearings in place, and between that plate and the extruder assembly. The first step is to get the extruder assembly out of the road.

This is what the typical view of the parts you are going to work on:
Extruder and X axis bearing plate viewd from rear of printer.jpg

If you assembled the printer by following the video instructions, then you will have the nuts of the three screws (which form a triangular pattern) facing you and the screw heads hidden behind the extruder. Grab a pair of pliers to grip the shafts of the screws and then undo the nuts. Undo the screws which are in a straight line pattern and everything will fall away.

Take the plate which holds the linear bearings and extruder assembly and the three screws and nuts. Put the screws through the plate so the nuts will be between the plate and extruder assembly. Screw the nuts on a few threads so they hold on the screws. Now grab some painter's tape (or any thin tape) and wrap it around the screws under the nuts. Apply a few dabs of epoxy glue to the flat sides of the nuts and pull the screws through the plate so the nuts contact the plate. Set aside until the glue dries.

Printers tape around screws before gluing.jpg

Once the glue has dried, unscrew the screws and discard the tape.

Fit the plate so that the linear bearings are in their slots and temporarily hold the plate, bearings and rods together with a zip tie.
Bearing plate held in place with Zip tie.jpg

Now loosen the screws holding the stepper motor enough to move the stepper to the centreline of the printer. The nut of a screw on the Z-axis frame will prevent the X-axis stepper from moving the end of its slots. Live with it.
Screw preventing further loosening of X-axis stepper.jpg

Check the security of the belt around the right hand screw of the line of screws. Replace the zip tie if necessary. Push the assembly all the way to the right so that it is hard against the right hand Z-axis assembly.

Bearing Plate hard up against Z-axis assembly to permit tensioning of belt.jpg

Making sure that the teeth of the belt are inside the loop, grasp the loose left hand end of the belt and pull like crazy to tighten the belt. If you can grasp the axle of the stepper motor turn it anti-clockwise (that's counter-clockwise) to get a bit more tension. Temporarily secure the tag end of the belt with a clothes peg, or small bulldog clip. Permanently secure the belt around the left hand screw with a zip tie. NOTE: BOTH SCREWS WILL POINT TO THE SIDES OF THE PLATE AS THEY ARE UNDER TENSION. NO PROBLEM, IT WILL COME GOOD LATER.

Once these belts are secured to the screws, place a lever between the left hand Z-axis frame and the X-axis stepper motor. Using the lever, and superhuman strength, move the stepper motor to the left and when it has gone as far as you can move it, tighten the four stepper mounting screws. Pluck the upper section of the belt. It should produce a deep mellow sound like a cello.

Since you've got the extruder assembly detached from the printer, its a good time to clean off some gunk. Soak some acetone into a tissue or paper towel then pack it around the extruder nozzle and surrounding parts. Go have a suitable beverage break, leaving the acetone soaked paper to do its thing. When you come back, you'll find that the acetone should have softened the gunk, making it easier to get off. You might like to remove the hobbed bolt and its gear wheel and clean out any gunk in the teeth in the shaft of the bolt, of in the cavity of the filament feed. Sparingly apply some light machine oil to the bearing in the extruder assembly. You might like to lubricate all the other bearing in the printer at the same time. But don't go splashing the oil about. It will only attract dust and particles of filament.

Pop the three nuts into the nut slots of the extruder plate and refit the extruder assembly to the X-axis bearing plate.

Job done!

Now attach the extruder