A printed x-carriage for Anet A8 MK8 Extruder with 37mm long stepper (stock one).
Designed for Igus RJ4JP-01-08 bearings but any 15mm diameter, 25mm long bearings with locking notches should fit.
It has mounts for 12mm and 18mm round capacitive/inductive sensors and for BL Touch.

There are added files for mold to make a silicone sock. It protects hotend from air from part cooling fan and carriage from heat from hotend.
Sock should not touch carriage while mounted.

Additional parts need:

• 4-5x M3 5-6mm long countersunk head screws or similar inch size
• 2x 2mm zip ties to secure cables
• probably longer screws to fix extruder.

It saves about 200-210g (with Igus RJ4JP) of weight compared to stock carriage with ball bearings.

It can move much faster than stock carriage. I was able to go 350mm/s with 6000mm/s2 acceleration (compared to 200mm/s with 2000mm/s2 on stock carriage with igus).
https://youtu.be/cSDkcCs6OD8

Before printing whole carriage you might consider printing test part (50% of it's height should be enough) to check if bearings will fit and if it won't bing on rods.
I don't recommend using Cura 3.x.x for slicing as it has problems with dimensional accuracy.

06.05.2018
Redesigned bearing mount. This one should work better.
Still no bed sensor mounts. Working on 2: BLTouch and 8/12/18mm capacitive/inductive sensors.

09.05.2018
Redesigned blower fan mount. It is on separated part from extruder mount and with bed sensor mount.
It is fixed with 4 M3 5-6mm long countersunk head screws or similar inch size, I think it's size 5 (0.125)

14.05.2018
Almost done. Had to change few parts because I couldn't put stepper in.
Also changed height of sensor mount.
And one last thing - hotend silicone sock (like this https://www.thingiverse.com/thing:2847635) is a must as hotend is really close to carriage and with out sock it will melt.

16.05.2018
Added a test BLTouch mount. Will have to check how strong it

26.05.2018
Redesigned some parts. Added part to direct extruder fan air to cool bottom part of carriage so it won't melt from heat block.

13.06.2018
I think it's final version. It's been printing for 2 days without any problems.
I'm not sure about BL Touch sensor mount height. It's been made based only on calculations. There is added a spacer if you need it to be lower.