This is a modification of the mendel90's x-carriage that adds a z probe. When used with new firmware (MatterPrint3D) your mendel90 can auto calibrate the bed height and dynamically compensate to ensure level.Stuff you will need.1 - printed x-carriage 1 - printed z-probe-mount 1 - printed up-down-bar 5 - 2.5m x 12m socket head cap screws 1 - 3m x 25m socket head cap screw 4 - 3m washers 1 - 3m nyloc nut 1 - mechanical limit switch 2 - 10mm x 5mm x 3mm neodymium magnets (ours came from a sonicare brush head) MaterPrint3D firmware: https://bitbucket.org/MatterHackers/matterprint3dProcedureYou can read our article and see videos at: https://www.matterhackers.com/news/automatic-printer-calibration-updateCurrently MatterPrint3D is only set up to work with RAMPS boards. If you have another board you will have to get the z-bed switch working on the z-min switch for your printer. If you do, we would love to have your patch.Have fun printing,Lars.