The original design uses a washer on each side of the bearing like this:
When the belt is going off the bearing, it will start to grind against the stationary washer. This will cause a lot of extra friction, which the stepper motor must overcome. Only way for it to overcome this additional friction is to draw more power, and to do that, it must be turned up on the stepper drivers.
While this isn’t directly a problem, because the stepper drivers easily can provide the needed power, the problem is that both the stepper drivers and the stepper motors are getting a lot hotter than needed, plus the wear on the belt is also increasing.
What is this then?
These are sleeves are made on a high precision CNC lathe, and is in aluminium to keep the weight down while still providing plenty of strength. The goal here is to eliminate that stationary wall the belts could ride on, and by pressing the sleeve directly onto the bearing, this have been achieved. The sleeve will still guide the belt so it won’t come off the bearing, but the wall guiding it will move at the same speed as the belt, and therefor not give any additional friction or wear on the belt.
The sleeves are made to fit the 5mm wide 5T polyeurathane timing belt
Perfect pully position
While removing the friction generated between the washers and the belt, the sleeves also make sure to guide the belt to the best position on the pully.