Ender 3 IDEX Edition

This is an IDEX conversion for the Ender 3 and Ender 3 pro. The files here include the two X-axis motor/idler mounts, belt mounts to use the ApolloLander toolhead with this setup (see below), and an optional drag chain mount. I printed all my parts in ASA (4 perimeters/30% infill), but PETG might also work.

Bill of materials

1. Official Creality dual Z kit
2. MGN12 linear rail, 450mm, with 2 carriages
3. 10x11mm drag chain (whether this is necessary depends on your choice of toolheads and cable routing)
4. NEMA 17 motor, 42mm (x2)
5. 20T pulleys (for 6mm belts) for the motors (x2)
6. 20T idlers (for 6mm belts, M3 bore) (x2)
7. GT2 belt (approximately 2.5m)
8. M5x50mm BHCS screws (x4, for mounting the printed parts to the gantry)
9. M5x20mm countersunk screws and nuts (x2 each, for tensioning the idlers)
10. M3 heat set inserts (4mm)
11. Variety of M3 BHCS screws, washers, and nuts
12. Toolheads (see below)
13. Toolhead boards and/or new mainboard to support the extra motors, hotend, fans, etc.

Assembly instructions

1. Print all parts for the X gantry; you need two of the covers and idler mounts and one of each front and back bracket (8 pieces total, excluding the toolheads). 
2. Insert heat-set inserts in the two back brackets.
3. Remove the X motor, X idler/tensioner, toolhead, and belt from the X gantry.
4. Mount a motor to each front bracket.
5. Install the second Z axis (if not already done).
6. Remove the wheels by removing the screws holding them. Pay attention to where the spacers, washers, eccentric nuts, etc. are placed, since you'll have to put them back soon.
7. Using M5x50mm screws, reassemble the X gantry onto the printer with the front and back brackets on each side “sandwiching” the metal plates and wheels/spacers.
8. Attach the linear rail to the X gantry using M3 screws and T-nuts.
9. Assemble the idlers into their mounts.
10. Run the belts through the idlers and motor pulleys. One belt should run above the gantry (with the ends facing up) and the other should run below (with the ends facing down). The bottom side of the top belt and the top side of the bottom belt will run inside the X gantry extrusion.
11. Mount the idler mounts to the front covers and mount the front covers onto the gantry.
12. Build the toolheads and attach them to the carriages and belts.
13. Tension the belts and cut them to length
14. Install the drag chain mount to the original extruder mounting point and install the drag chains. I used 6 links for the left drag chain and 10 for the right, but you may need to adjust this depending on your toolheads.

Notes on toolheads

1. I expect that this mod will work with many different toolheads, as long as you can find a way to attach them to the rail and to the belts. One belt runs above the X axis and one runs below. Because the toolheads need to pass in front of the Z axis extrusions, toolheads that extend behind the gantry will not work.
2. The toolheads shown in the photo are based on the excellent Apollo Lander by squirrelf3d, available to subscribers on Patreon (https://patreon.com/squirrelf3d). See here for more information: https://www.printables.com/model/544890-apollolander-stock-hotend-dual-5015. I am including here models for the belt mounts that I designed for this IDEX build, but you will need to get the rest of the toolhead files from squirrelf3d's Patreon. 
3. Using a BLTouch or similar probe on the left of the Apollo Lander toolhead (as pictured) reduces print area by 15mm in X for each toolhead, but allows the entire bed to be probed. Placing the probe in front of the fan allows the entire print area to be used, but the back of the bed cannot be probed. These issues can be avoided by using narrower toolheads or by remixing the gantry parts to allow a longer 500mm linear rail.

Klipper configuration

I added my Klipper configuration, in case it's of use to anyone. The choice of board, pins, display, etc will almost certainly NOT match your setup, but a few sections (endstop positions, macros) may be useful.