During shipping, rough handling or over time it is possible for a gantry to come out of alignment on the Replicator 2 and 2X. This will be noticeable by your printer grinding because it won’t hit an endstop or printing objects at an unexpected angle compared to the front of the platform. This can be obvious on the initial bead of filament the printer primes its nozzle with at the front of the platform.
If your gantry is out of alignment, the first thing to do is check to make sure you don’t have any loose belts that caused this as fixing this and leaving a loose belt with allow it to get out of alignment again. Once you have all your belts properly tightened you can then begin the process of aligning the gantry.
To check the current alignment slide the gantry to the front of the printer and look at the space between the Y-axis Primaries (Holds the X motor and the X idler pulley) and the two front gantry rod holders(black plastic pieces in the top corners than the Y-Axis rods snap into). A properly aligned printer will have the same spacing on both the left and right side.
Now that you know which way you need to move the gantry to realign it, you can put a mark on the belt as a starting point. We generally work from the side the needs to move closer to the front but either way will work very similarly. Using a marker that will show on the black belt place a dot on the last tooth of the belt in the Y-Axis Primary. This is your starting point and you will be adjusting relative to that point.
To bring it back into alignment you should note roughly how far out the two sides are and then move the gantry into the middle of the printer. You will now simply pull the belt out of the side you are working on by pulling towards the middle of the printer, be careful not to pull too much or you can pop the bearings out of the front or back of the printer. Once the belt is out be careful to only move the gantry on the side you are working on and slide it in the direction you need to go relative to your mark you applied to the belt. Once you think you found the tooth you want turn the belt 90 degrees to the entrance for the teeth and it should be easy to rock it into place again. Check your alignment and fine-tune if necessary using a count from your mark as a way to maintain some degree of accuracy.
This method is one of the quickest ways we have found to align your gantry. MakerBot suggests a different way that makes use of the set screws and has a video of it you can check out here. They both end up with fairly similar results.