Note: This is for the newer Ender-3 printers with the U-shaped front Y idler bracket. Here's the mod for the older style with the flat/z-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
- 1 x M8x60mm or 1 x 5/16x2-1/4" bolt
- 1 x M8 washer or 5/16" washer
- 1 x M8 locknut or 5/16" locknut
- 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 8mm_bolt_spacer.stl @ 0.2mm, 2 shells, 100% infill
- 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_v2.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 Y idler bracket to give the Y belt some slack & remove the stock 8mm bolt holding the front Y idler pulley & spacers on. Note: You will not reuse the stock 8mm bolt & locknut since the bolt is too short & the locknut may not have the same thread pitch as the new bolt. Unhook the belt from the Y plate and set aside as it will be reused later on. Remove the four screws & v-wheels holding the Y plate to the extrusion.
- Insert the M8x60mm or 5/16x2-1/4" bolt through the front idler bracket while using 8mm_bolt_spacer.stl as a spacer with the bolt coming out to the right side of the bracket. Add 1 x M8 washer or 5/16" washer, one white spacer, the two halves that make up the idler pulley, add the second white spacer & then tighten everything down with a M8 locknut or 5/16" locknut. See the first picture for details.
- Once all hardware is removed from the Y plate, use ydrillguide_remixed_v2.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 the Y plate 180 degrees. Use the pictures from the original mod 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 four 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!
Video for previous version: https://youtu.be/IBlSbVZZRGk
Any feedback, questions or comments are welcome!