If your prints are turning out significantly smaller in size in one direction, it is possible that it is being caused by backlash. This is when the extruder isn’t being moved as far as it should to make the proper size. The reason the extruder won’t move far enough when you have backlash is that due to a loose belt, the teeth of the gear allow slight play on the belt causing the extruder to drag as far back as possible on its teeth because that is where it will actually catch. Any change in direction immediately moves it to drag the opposite side, this means the very edges of your print won’t ever be reached properly.
Loose belts can be more severe as well if they allow slippage to occur and miss-align your gantry, but the solution to a loose belt is generally the same regardless of severity.
There are 4 belts to confirm are tight on your printer, 1 on the X axis and 3 on the Y axis. The two main ones that come loose and cause issues are the X belt and the short belt that runs from the Y motor to the pulley above it. The other two belts that run front to back in the top of the printer are snap-fit and naturally are tight. If they aren’t tight it is likely you need to re-seat the bearings and pulleys in your upper corner of the printer or a part is actually damaged.
As for how tight to tighten you don’t need the belts to be super tight but they should be firm and it should feel like there is no play or slop if you go to Utilities > Enable Steppers and then try to wiggle the gantry around a bit. There are many causes for play in your gantry so if you can’t get rid of any play with a tight belt, check out our other posts or give us a shout and we can help you diagnose it.
Tightening the X Axis Belt
The X axis belt is tensioned using the position of the X motor. To adjust it’s tension you simply loosen off the 4 bolts on the X motor(it is a weird position so removing the right side of the printer can help, especially on a Replicator 2X). When loosening bolts these they don’t need to be loosened much and completely removing them can make it difficult to reassemble due to their location. Once they are loose, push on the left side of the motor to add more tension to the belt and find a tension that feels about right. Next tighten the 4 bolts starting with the easiest to reach as they will help keep the tension while you get the other ones tight. Once the bolts are tightened double check your tension.
Tightening the Y Axis Motor Belt
On the Y Axis, the main belt that will come loose is the one that connects the Y motor to the pulley in the upper corner. Tightening this belt is very straightforward. You will need a 5.5mm socket or nut driver for the nuts that secure the motor. To tighten this belt you will loosen the two nuts that hold the Y motor in place, press down on the Y motor and then secure the two nuts.
Note:This belt should have much less give than the other belts as it is significantly shorter.