The item called columnClamp is a screw wave reducer: it utilities the unused height to shorten the free screw length. Two bronze bushings from the list below are inserted at the top and the bottom of this waveReducer.
No need for automatic bed leveling neither endstops.
Black columns are igus AWMR12 alu tubes with ceramic coating 500 mm long inserted in them M8 screws and fixed with super glue. For those rods use lm12uu or igus bushings.
The driving screws are igus PTGSG08X1501R500ES - if you cannot print the nut well or have extra $75 then order with the screws the DST_JFLM_202020DS8X15 nut, because it has no play and rolls down the thread under own weight.
The best extruder I know ;) is saintFlint: it's best location at the bottom of the top plate - just replace one original screw with a longer one