Prusa i3 Mk2 / Mk2S / Mk2.5 PSU spacer by triplepoint

Last crawled date: 3 years ago

I have a Prusa i3 MK2 kit (shipped Feb/2017), which has since been upgraded to a Mk2S (Oct/2017), and then a Mk2.5 (Apr/2018).
Judging by the bed-leveling search pattern, the vertical frame on this printer has always seemed a few millimeters too far back on the Y-axis threaded rods. This has resulted in sporadic XYZ failure-to-calibrate issues.
One solution proposed by others with this issue was to unbolt the power supply unit (PSU) from the back-right corner of the Y-frame (first picture), allowing the vertical frame to be moved forward the required amount. This worked, but it leads to a reduction in stiffness in the frame.
My solution here is to print a spacer to go between the PSU and the vertical frame (2nd and 3rd pictures). This allows the vertical frame to shift forward on the y-axis, while still being securely bolted to the back-right corner.
To determine the thickness (6.88 mm), I unbolted the PSU from the vertical frame, reattached it to the back right corner of the y-axis foot, and moved the z-axis frame further forward on the y-axis's threaded rods, until the bed-leveling search algorithm was centered in the y-axis on the marker points on the heated bed. Then I could simply measure the gap between the vertical frame and the PSU, and print the part accordingly.
See a more complete description of the issue here:https://github.com/prusa3d/Prusa-Firmware/issues/616#issuecomment-385211047