Linear Rail Z Ender 3 NG with Trident-like Bed Carriage

Introduction

The motivation for this design was the lack of a tilting bed for the beta version of the Ender 3 NG. The LM12UU bearings I had on my linear rods were sloppy, and I kept accidently pushing down on my top frame, sending the 12mm rods through the bottom frame blocks. I had the idea to use linear rails and a couple extrusions to replace the rod setup when RH3D posted a teaser of the v1.2 NG with his 'Ulitmate' frame configuration. From there I mimicked the tilting carriage of the Voron Trident and moved the Z steppers below their leadscrews so a floor panel could be fitted later.

BOM

https://docs.google.com/spreadsheets/d/1q0P1SEcmE_g-YO1ZnrnVouiFdbZVGAW0y-GpTiRIaFc

Installation

Drill blind holes and tap extrusions where needed
Install as if building the “Ultimate” E3NG frame but join 2040 extrusions to the front of 4040s instead of the top.
The rear 2020 should be installed during bottom frame assembly.
For lower front corners, use hammer t-nuts to hold against the 2040 and screw into the 4040 ends as usual.
Front idler blocks also installs as usual.
Motors mount to blocks that screw into heat inserts on the bottom side of lower front corners and use t-nuts against extrusions.
Linear rails ought to be installed on the broad side of 2040s in the furthest v-slot.
The rail-side of the bed arms come in 2 pieces that join together with M3x6 screws.
Affix the joined part to the MGN sled with M3x8 screws.
Leadscrew nuts are held on the bottom of these parts with 2-4 screws threading up into M3 nuts on the top side.
The bed carriage is assembled from two 2020 extrusions with a blind hole is drilled halfway down the 300mm extrusion where the 200mm extrusion joints.
Bed side printed parts use M5x12 bolts into M5 roll-in t-nuts. Do not tighten these fully until the carriage is mounted level.
GE5C bearings must be held into the bed-side parts with Mx6 screws.
M5x16 screws go through the GE5C bearing and standoff on the rail mount. An M5 hex nut must be inserted in the bottom of the rail mount to hold the fastener in place.
To mount the bed, use M4 roll-in t-nuts a spacer, and a flat head M4 screw.
Only fully tighten the rear-most screw. The others should be just barely loose for bed expansion.
Lead screws are best installed near the end of the build and held to the shaft of their motors with a 5mm to 8mm coupler.

Additional Notes

While a skirt is not required, it is recommended. At the very least, this mod will need the frame raised up on legs to keep the printer from resting on the Z motors. To fit inside popular skirt designs without without contacting a bottom panel, motors can only have a body length of 40mm or less.

Some Ender 3 owners have upgraded their machines with MGN9H or MGN12H linear rails. There are models that mount to either carriage.

Oldham couples can be used to reduce or eliminate z-banding from bent leadscrews. Couples that compensate for misalignment between the leadscrew and motor shaft may further reduce print artifacts along the Z-axis. Examples of both, which I have installed on my machine, are linked in the BOM.

Rear panels have large passthroughs added for cables to run between a bottom compartment and the backpack. The top partition that sandwiches between motors and motor mounts is adjusted to fit a 2020 extrusion for installing the rear linear rail. 2040 extrusions of 350mm length are used in the front of the frame, replacing 12mm linear rods. These hold the frame together more rigidly when using blind joints, give a mounting location for the front 2 Z linear rails, and look great with the rest of the frame. They also happen to be the same extrusions you'd order to replace the printed frame parts in the rear.

If you have any questions, the best way to contact me is through the RH3D Discord @Joushoutai. STEP remixed from the E3NG CAD will not be uploaded.

UPDATE 04-09-25: Remodeled left/right extrusion arm and MGN12H carriage geometry to fix clearance issue.

UPDATE 05-09-25: Added bed arms for the original Ender 3 carriage plate. New holes must be drilled in the plate according to the E3NG v1.2 build guide. These arms include modelled supports which may be difficult to remove. Please plan accordingly when slicing these to print.