I had a difficult time getting the belt tension I was looking for when assembling the MK3 printer. I wanted more adjustment then what is available by rotating the stepper motor when tightening. Once assembled it is also difficult to get back in and tighten the belt on the X-Axis carriage. So I designed a simple plate that mounts to the motor and has slots to allow for tightening the belt. Assemble the plate on to the X-Axis motor with (4x) M3 x 10mm screws, I had these in my Spare Parts Bag. Install (3x) of the square M3 nuts (also in Spare Parts Bag) in the slots then assemble to the mount, leave slightly loose. I used a screw driver between the motor and the frame for leverage to get the belt tight and then fully tightened the 3 screws. I also flipped the pulley on the motor around 180 degrees so the belt was aligned inside the slot.

Update 1/22/18
One of the users who made this for an MK3, needed to increase the center diameter to 1.0in to fit the stepper motor. The center locating diameter on my MK3 stepper motor is 22mm, which is the original bracket STL. I added a second bracket with a 1in center diameter in case anybody else has the same issue.

Update 10/30/18
Just FYI, I was informed this does not work with the new MK3 built in X-Tensioner design. So unfortunately can't use both at this time. Thanks.

Prusa

Prusa Mk2

No

No

0.2mm

100%

Printed on MK3 with standard PLA with 100% infill and no supports. I had the counterbored holes facing down, and just needed a little cleanup inside them after printing.