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

[old man emu]

There are three things that affect the tension of the Y-axis belt:

1. Location of the stepper motor in its mount
2. Length of the belt
3. Length of the large threaded rods.

The first step in tensioning the belt is to back off the two inner nuts on the front plate which holds the idler bearing. This will allow the plate to move towards the stepper motor, loosening the belt.

1. Location of the stepper motor in its mount:

The four screws which attach the stepper motor go through slots in the support assembly. These slots permit the stepper to be moved about 1/4" (6mm) towards the rear frame plate for adjustment of the belt tension. When adjusting the tension of the belt. fit the stepper so that the screws pass through the ends of the slots furthest from the rear frame plate. Tighten down the stepper motor.

2. Length of the belt.

Assuming that the belt has been cut to the correct length, locate the screw nearest the stepper motor which goes through the attachment bracket and pass a short tag of belt around it, making sure that the teeth of the belt are on the inside of the loop. Secure the tag to the belt using a thin cable tie.

Feed the long length of belt around the idler bearing from the underside of the printer to the top.

Loop the belt around the toothed pulley attached to the stepper motor shaft.

Pass the end of the long length of belt around the idler bearing from the bottom of the bracket, making sure that the teeth of the belt are on the inside of the loop. Apply some tension to the belt by pulling the tag towards the front plate. The tag should not be more than about 1" (25 mm) long. Secure the tag to the belt using a thin cable tie.

Unscrew the outer nuts on the threaded rods until the end of the thread is just protrude from the nuts. Then wind the inner nuts against the inside edge of the front plate until the desired tension is obtained in the belt. (It is said that the correct tension is reached when the sound made by the plucking of the belt is similar to the bass tone of a cello.) To obtain more length of threaded rod, loosen the outer nuts on the rear frame plate by a few threads, then tighten their corresponding inner nuts against the back plate.

Y-axis belt tensioning.jpg Y-axis threaded rod exernal nuts.jpg


Old Man Emu