SeeMeCNC Rostock MAX v2 User Manual page 118

If you're a mere mortal like the rest of us poor suckers, you're going to have to make an
additional adjustment. Delta configuration printers like the Rostock MAX v2 have a very interesting
geometry that will result in the hot end traveling in a non-flat path if it's not perfectly calibrated. This
tiny error will express itself as a "virtual" convexity or concavity in what it thinks the bed shape is. If
your hot end is pinning the feeler gauge to the build surface, the error is expressing itself as a concavity
– the firmware thinks that it is moving flat, but the path of the hot end is actually concave and that's
why it pins the feeler gauge to the build surface – the center is actually lower than it should be. The
reverse is also true – if the hot end is not touching the paper at all, it thinks that the bed is dome shaped
(convex). This all boils down to what happens when the "perfection" of mathematics runs face-first
into the "imperfection" of reality. :)
The concave/convex shape of the bed is controlled by the EEPROM table entry labeled
"Horizontal radius [mm]".
Fig. A-7:Horizontal Radius value.
What you're going to do is change that figure by 0.5 until the nozzle is touching the paper just
the same as it was when you calibrated at the base of each tower.
In order to lower the nozzle, you'll need to increase the Horizontal Radius value.
In order to raise the nozzle, you'll need to decrease the Horizontal Radius value.
Each time you change the Horizontal Radius, you must re-calibrate the base of each tower as
you did in the previous steps using all four macros in the Z, Y, X, Bed Center order.. It may take a
number of iterations to get the center nozzle height nailed down, but it IS worth the hassle. Your first
layer quality and plastic adhesion require that the nozzle track across the entire bed as perfectly flat as
it can.
Please make sure you click the Save To EEPROM button each time you make a change,
otherwise the new Horizontal Radius value will not take effect!
That's all there is to it!
Rostock MAX v2 User's Guide
Appendix B: Alternate Calibration Method - 118