Belt tension will loose over time
X Axis Layer shift
1) Check the 2 bolts which attach the hotend to the carriage. Thighten them if they are loose.
2) Check X belt tension, thighten the belt Will help.
Y Axis Layer shift
1) Check Y belt tension, thighten the belt Will help.
2) If the build platform is wobbly, check Y Axis wheels. Tighten the eccentric nuts if any of the wheel can be spun freely.
How tight should it be?
So far still no one can defind how is too tight yet, but it’ll have to be tight until a certain extend, else if it’s too loose, the layer shift may occur.
The disavantage of super tight are:
1) The bolt that hold the bearing or iddle pulley may bended, and the belt may start rubbing the edge of the aluminium extrude,
2) Tt may break the belt, commonly from the point where the brass stopper that slot in to the carriage.
Share with us in the comment if you encounter some other issue that could possibly causing layer shift, and how you solve it.