This is an upgrade for a printrbot simple to be able to use e3d hotend. I am using the e3d litev6. The motor sits nicely on the top of the rods and the e3d hotend is mounted on the bottom of the extruder board so there isn't any need to modify the old printrbot fan that you use to cool down the PLA. UPDATE - now you can add auto-leveling probe I have printed everything with 25% infill and it is holding fine. You don't have to modify the printer at all. Just the firmware as it is in the manual of e3d. The extruder bowden nicely holds in the printrbot metal extruder so no need to print any other extruder parts. Feel free to leave feedback Now you can add auto-leveling probe - need to modify the firmware for that