First it is important that the adjustments to the holes as outlined in the “unflat bed” thread are done before assembly, particularly adjusting the countersunk holes such that the screws sit level with the top of the heated board. It is also advisable to check the flatness of the aluminium plates using a steel rule across the surface and making careful adjustments to make it better. You will notice that there are several burrs from the machining process that should also need to be removed; on mine these measured up to 0.5mm and definitely affected the flatness.
The assembly notes for height adjusters should say that the top adjuster must be set to around 6mm from the plate so that there is adjustment space available when levelling the bed. It also helps to use a spot of cyanoacrylate adhesive to hold the nuts in the adjusters in case you need to remove the plate later. Doing this made levelling the bed very simple, as it should be.
It could be better to fix the bed with M2.5 ( 2.5 mm ) screws instead of M3 ( 3 mm ), instead of making the holes larger.
You can also use a dial micrometer ( about 20 Euro ) to adjust te bed.
It is actually impossible to get a flat bed with just a PCB-Heated bed.
You have to use a glas plate (Kapton coated for ABS, Blue Painters Tape for PLA). Clip that on the PCB Heater with some bulldog clips and you will have a perfectly smooth and adjustable surface.
If you want, there even are some projects out there to “auto-level” your bed with the Z-Axis motor.
Unfortunately, the K8200’s z axis follows gravity when lowered – at least with my printer, there is severe backlash/reverse clearance (not sure about the correct translation of the german term “Umkehrspiel”), since the M8 nut that is used to move the z axis is sitting quite loose vertically.
