How to adjust the tension of the belts (BCN3D Sigma)

In this article we will cover the procedure to adjust the tension of the belts in your Sigma. 

All printers are shipped with the belts adjusted from factory, so unless you are experiencing layer shifting issues or your belts have lost tension over time, there's no need to adjust these.

To adjust the belts you can use our printable tensioner as a reference. You can download the STL file and the instructions on how to use it below.

Notice that this tool is not updated and its precision may vary on each print, so it should only be used as a reference point and to ensure that the tension is the same in the paired belts for X and Y.

To learn how to adjust the tension on each of the belts follow continue below:

X axis belts adjustment

1.Slightly loosen the two lower screws to release the tensioner from the X belt. Make sure to loosen these carefully to prevent them from falling off the plate.

2. Adjust both upper idler screws in order to increase or decrease the tension, making sure that both are adjusted equally. Once the tension is right, tighten the screws adjusted in step 1.

belt-tension-1X

Y axis belts adjustment

3. Loose both side bolts to loose the belt idler.

4. Adjust both front screws to increase or decrease belt tension. Once the tension is right, tighten the screws adjusted in step 3.

5. Make sure that the external faces of the idler and the holder are parallel before finishing the adjustment.

belt-tension-2Ybelt-tension-Y-paralelism

Y motor belt adjustment

Notice that, if you are using the tensioner tool, it is not suitable for the adjustment of this particular belt.

To modify the belt tension, loosen the two nuts that hold the stepper to the printer’s
structure without removing them, using a 5,5mm metric sockets wrench.

Unload the filament and remove the right upper bowden tube from the printer to ease this procedure.

belt-tension-Y-short

Below the motor there is a rectangular piece with two hollow screws in its lower part.
Adjust them equally using an allen wrench, to increase/decrease the belt’s tension.

Once the belt tension is adjusted, tighten the two nuts adjusted on the first step.

belt-tension-Y-short2