This is a piece I built to support the Y idler pulley on my Makerbot.

As shipped, the Y idler on the Makerbot is just a plastic pulley on a bolt screwed into the baseplate. This is really not a good design. The baseplate can flex, which makes it hard to properly adjust the belt tension. The pully is bare plastic turning on a fixed metal axle, without even a bushing, and can after a while get very noisy.

This modification adds a bracing arm which attaches around the end of one of the Y rails, using the same hex nuts that hold the Y rail end cap on. You will have to use longer screws to account for the thickness of this piece. Two bearings are pressed into the piece, and these now support the 4mm bolt that the pulley turns with. This makes the Y stage much quieter and smoother, and makes it easier to properly adjust the Y belt tension.

Warning - this is an experimental piece and may require some trimming to fit properly, some of the clearances are really tight. This is uploaded for reference purposes only.

Print out the part. Trim as needed.

Take two ball bearings (13mm OD, 4mm ID, 5mm thick) and press them into the pockets in the piece.

Remove the 4mm bolt which holds the Y belt idler pulley in palce. You might have to trim the pulley or the part slightly to make it fit. You also need to keep the belt looped around the pulley as you do this as there's no way to install the belt afterwards.

Insert the 4mm bolt through the bearings and pulley, and use a single 4mm hex nut to lock the bolt, bearings, and idler pulley together.

Remove the end cap from the right-side Y axis rod on your Makerbot. Slide the rod out. Put the idler support where the end of the rod goes into the frame on the Makerbot. The bottom of the 4mm bolt that secures the idler pully will stick through the hole in the baseplate, but should be able to turn freely.

Slide the Y axis rod back in, and then attach the rod end cap with four 3mm nuts and screws.

Re-adjust the belt tension and reconnect anything else you disconnected. Your Y axis should now be quieter and smoother.