LRX-B MGN12H linear rail mount for Creality CR-30

Now you too can rail your weird angled CoreXY belt printer!

This bracket is designed specifically for the Creality CR-30 and mounts the linear rail to the back of the X carriage. This is done to retain the original placement of the X carriage itself which helps with positional accuracy. 

Misalignment of the belts can cause weird positional errors that can't be easily rectified with rotation distance calibrations (or step/mm adjustments in Marlin) if the placement of the carriage is grossly out of wack - Which it could be with the rail mounted to the front unless you were to redesign the carriage to push the belts back behind the carriage.

I like simple and elegant enough though, so I see an issue and I resolve it in the easiest way I can think of… Which in this case, is to mount the rail to the back of the printer and preserve the X carriage position as best as possible.

Surprisingly, this approach doesn't cause any additional flex in the carriage from my own testing!!

To do this upgrade yourself, you'll need;

1x 300mm MGN12H linear rail with bearing block (remember to grease it before use!!)
At least 6x M3 T-nuts
At least 10x M3x5 screws
The original bolts from the V-slot wheels

I'd advise keeping the nylock washers in case the printer you use to print this part results in the tolerances being lax enough to allow the bolts to slide straight through the carriage, but when I tested this carriage (which was printed on a machine that has full XY size compensation and skew correction), the carriage bolts actually locked into the X carriage block without needing them.

When installing this carriage, you don't have to de-tension or remove the belts. Disassembly of the hotend is recommended, but also not mandatory.

INSTALLATION:

1: install the linear rail to the BACK of the X carriage with 6x M3 screws and T-nuts

2a: If you have any direct drive modifications (e.g BMG mount like mine, an Orbiter, Sherpa or otherwise) I strongly advise removing the extruder assembly from the X carriage for step 2b to reduce the amount of weight the belts will be holding onto. This will make the X carriage more manageable while it's held up by the belt tension.

2b: remove the four bolts that hold the V-slot wheels onto the X carriage.

3: Grease the linear rail, then install the carriage mount onto the bearing block of the linear rail. The two mounting holes spaced closer together should be on the UNDERSIDE of the X carriage and the wider ones on the top. Use 4x M3x5mm screws to bolt this securely into place.

4: Install the 4x X carriage bolts through the X carriage and into the X carriage mount. If your screws don't go tightly into the X carriage mount, use the nylock washers from the V-slot wheels to lock them into place. If like mine, they screw in fairly tightly into the X carriage block, you can actually get away with not installing the nuts if you want, or still do so after tightening the bolts up to add extra protection from the screws potentially backing off and out of the X carriage.

once that's done - boot the machine back up and perform your Y axis height adjustments to confirm the upgrade hasn't messed too much with your bed levelling.

And on a tangent - 

If you're wondering wtf that orange block on top of my hotend is; it's a bowden tube mount to allow me to use an Ender3 KE hotend on this machine. once I've refined the designs for this part so it fits without needing to be adjusted with a knife I will make it available.