Note:This is for the older Ender-3 printers with the flat/z-shaped front Y idler bracket. Here's the mod for the newer style with the U-shaped front Y idler bracket.
The original design placed the belt too close to the frame which caused severe belt misalignment. This could be due to my unit being an early model, poor QC or a number of other reasons, so I moved the holes for the belt retainer blocks out 4.6mm.
I figured I wasn't alone in my endeavor to fix a wobbly bed, so I wanted to make this remix available. A HUGE shoutout goes out to goopyplastic for doing most of the heavy lifting on this design. Don't forget to degrease your rail & carriage. Pre-lube everything if you want to do it now or save the mess & wait until its mounted.
- 1 x Ender-3
- 1 x 300mm MGN12H linear rail
- 2 x M4x20mm screws
- 2 x M4 t-nuts
- 2 x M4 washers
- 4 x M3x25mm screws
- 16 x M3x8mm screws
- 12 x M3 t-nuts
- 4 x M3 locknuts
- 12 x M3 washers
- Printed parts from Print list below
- 1 x yretain.stl @ 0.2mm, 2 shells, 100% infill
- 1 x yretain-mirror.stl @ 0.2mm, 2 shells, 100% infill
- 1 x ylimitspacer.stl @ 0.2mm, 2 shells, 100% infill
- 1 x ydrillguide_remixed.stl @ 0.2mm, 3 shells, 15% infill
- 2 x Linear_Rail_alignment_helperMGN12+_V-Slot_2020.stl @ 0.2mm, 3 shells, 15% infill
- 4 x mgn12-rail-stop.stl @ 0.2mm, 2 shells, 100% infill. You'll only need two, but they tend to break if printed with PLA due to the snap on fit. These replace the goofy red stops included with most rails.
- Remove all four bed leveling knobs & lift the heated bed & springs out of the way.
- Loosen the screws on the front idler to give the Y belt some slack & slide the belt off the Y plate. Remove the four screws & v-wheels holding the Y plate to the extrusion.
- Once all hardware is removed from the Y plate, use ydrillguide_remixed.stl to drill 1/8" (3.2mm) holes by aligning it in the holes where the vslot wheels were mounted. Note: There's an additional set of holes for different hole patterns of mgn12 carriages, so check which spacing your carriage has to avoid drilling unnecessary holes. Use larger drill bit or small file to deburr the holes.
- Mount the yretain.stl & yretain-mirror.stl blocks to the Y plate using 4 x M3x25mm screws, 8 x M3 washers and 4 x M3 locknuts. Pay attention to the orientation of the Y plate as this mod rotates Y plate 180 degrees. Use the pictures for guidance.
- Mount the 300mm MGN12H rail to the extrusion using using 12 x M3x8mm screws and 12 x M3 t-nuts & at least 2 x Linear_Rail_alignment_helperMGN12+_V-Slot_2020.stl as alignment blocks. Then mount the modified Y plate to the carriage with 4 x M3x8mm screws and 4 x M3 washers.
- Relocate the Y-motor mount (leave the motor attached) & front idler assembly to the opposite side of the extrusion & re-mount with existing screws/hardware. Keep the three screws holding the front idler on a little loose as we'll use this slack to install the belt and tension it. Note: newer models will need a longer bolt as the front idler mount is different.
- Relocate the Y-axis limit switch using ylimitspacer.stl, 2 x M4x20mm screws, 2 x M4 washers and 2 x M4 t-nuts to the opposite side of the extrusion. If you tilt the switch back while tightening it, it should fully register on the edge of the bed mounting plate.
- Reuse the stock Y belt and attach it in the same insert-into-slot fashion as stock. Re-tension the belt by sliding the front idler forward & tighten the three screws.
- Add your favorite oil or grease to the rail (you degreased the brand new one, right?)
- Do the reverse of Step 1 & re-level the bed.
- Move your z limit switch up a few mm's/until your nozzle doesn't crash into the bed when homing.
- Print away!
Any feedback, questions or comments are welcome!