WARNING:

This case was designed to fit the stock Creality board.

Although this case was never "advertised" as being designed for them, the V1.0 and V2.0 revisions of the BigTreeTech SKR Mini E3 also fit as they are the exact same size of the stock Creality board.

Unfortunately, the V3.0 revision of the SKR Mini E3 will not fit this case as BigTreeTech decided to slightly increase the size of the board, and slightly alter the I/O spacing.

Ender 3 External Electronics Case

External electronics case integrating the stock LCD mounting bracket for the Ender 3

Uses stock parts, stock screws, and stock spare cable ties.
You will however need to extend the Z-stop wiring by your own means.

Design includes a mounting clamp for the XT60 connector which allows the power supply to be plugged directly in to the case. It does not feature a fan grill because the stock Ender 3 fan is significantly quieter without one.

Make sure you read the installation guide below.

UPDATE: (10 June 2019)

Added modified version with the wiring hole moved to the rear for people with extended wiring looms. DO NOT use this version unless you have extended ALL of your printer's wiring (not just the Z-Stop).

UPDATE: (15 June 2019)

I bought a "quieter" fan from China that turned out to be louder and more powerful...
I gave it a try anyway, and found that the increased airflow caused the case to resonate and make an owl sound. With the stock Creality fan it's barely audible, but I decided to make a file revision to increase the outlet holes from 20mm to 25mm vertically, which gives a theoretical 25% increase in flow, and should help prevent the issue.

UPDATE: (30 June 2020)

Added a .STEP file for people to customize the case to their liking.
Sorry to those who previously asked for it and were ignored. Honestly speaking, I became frustrated with this "thing" for a long time and completely ignored it because there were significantly more people demanding I change it to their liking than there were people patting me on the head.
Huge thanks to Scott who tipped me the suggested $1 last month. That and a short mention in a Teaching Tech video really rekindled my interest in the design and spurred me on to finally finishing V2.

I also feel obligated to say that while this design was built completely from scratch, it was visually inspired by other similar designs. My original inspiration was this: https://www.thingiverse.com/thing:3382740, but that actually appears to be inspired by this earlier upload: https://www.thingiverse.com/thing:3313967

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INSTALLATION GUIDE:

(Some of these points may seem obvious, but I've added them to help beginners).

Run all screws through first to tap threads. It's much easier to make sure they're going in straight when the case is empty and not connected to anything. Don't over-tighten as you're only screwing in to plastic.

Test install your mainboard and make sure the SD card fits through the case and in to the reader. It's designed as a tight fit to make sure the card always goes inside the reader slot instead of over it, but sagging in the bridging can block the slot. Clean it up with a sharp knife if need be.

Before you unplug everything, take photos of all the wire locations with your phone. If you're not sure where something goes when rewiring the board, you can refer back to the photos. The connectors come from the factory with a glob of hot glue to stop them from falling out, you will need to peel this off.

Organise the wiring on the printer before you begin wiring the case. Make sure you leave enough length for full travel, then cable tie the wiring in a bundle. I find that going underneath the printer with the help of some printed feet gives you a few extra centimetres of cable length. The Z and Y axis stepper motor wires (4 pin) are the shortest, make sure they're at the top of your bundle and not tangled up which will lose you a centimetre or two.

You will need to extend your Z-stop wiring. Unfortunately there is no way to avoid having to extend it as the factory wiring is very short due to the Z-stop sitting right next to the standard electronics case. Polarity is not important, any cheap thin wire will likely do just fine. You need to add an extra 8 inches or so, but it's a safer idea to join the new wire at the mainboard end first, plug it in, route the new wire out to the Z-stop, then cut it to length and join.

There is a tunnel for a small cable tie under the wiring hole. It's U-shaped to make it easy to feed through, but I recommend doing this before you begin to add the wiring when you have more room for your fingers.

Because the case is very tight, you might find it difficult to wire the screw terminals while the board is inside. Pulling the wiring through as far as possible so it reaches out the top of the case, wiring the screw terminals "in mid air", then pulling the wiring back out and the board inside the case can make it a lot easier.

There's a small ledge on the floor (near the cooling outlets) for the board to sit on as it flexes quite badly when you push in the LCD connector. The board has a screw hole there, but the stock case doesn't use it, thus there is no supplied screw. I made a ledge instead to stick to the "only stock parts" design goal (plus it would also be very difficult to tap the screw straight with the overhang above). Remember it's there when you try to slide the board in if you're wiring it outside the case, because it's easy to get caught on.

If you're doing this it's probably because you want to enclose your printer to print with ABS. The stock Ender 3 case fan is linked to the part cooling fan, so if you have the part cooling fan off while printing ABS, the case fan will also be off, which can cause overheating of the stepper drivers. Cut the connector off the case fan and wire it in with the extruder fan at terminals (red with red, black with black) so the case fan stays on all the time.

The fan does not have a grill because test prints found that having a grill in front of the stock fan noticeably increases noise (a very big problem with the stock case lid too). Make sure the fan is lined up with the hole to reduce noise. It has a small amount of side to side play to allow for print inaccuracy.

Use the M3x6 screws from your stock mainboard case lid to secure the XT60 connector clamp (the hole is deep enough to fit up to an M3x10 if need be). You should be able to mount it after the board/wiring is in as it's offset to the side to clear the wiring, and the pins on the clamp will help hold it in place while you screw it down.

The short XT60 lead from the power supply will mean having to sit the power supply next to the case. Extending it is not necessary for the printer to work, but you can buy a pre-wired XT60 extension lead quite cheaply (or extend it yourself) if you want a cleaner work area. There are multiple designs of brackets here on Thingiverse for mounting the Ender 3 power supply behind or under your table/desk.

Consider buying some "self adhesive feet". They will stop the case from sliding around, reduce noise from vibration, and will only cost you ~$1 from Chinese online sellers.

EDIT: (15 June 2019)
I've realised that the wall width may be an issue for the USB port. The USB Mini B standard has a 7mm prong. The wall width is 2.5mm to prevent breakage during printing. With the slight inset of pins on the USB connectors, it should leave 2-3mm or so for the pins to connect, which should be more than enough. However if you find you are having connection issues, you can buy USB Mini B cables with a 14mm prong for a few dollars from China to workaround the issue. Just search for "USB Mini B 5 pin long".