SeeMeCNC Rostock MAX v2 Assembly Manual page 237

The nozzle tip is going to end up in one of three positions. It's going to be above your paper by
a visible amount, it's going to pin the paper firmly to the bed, or if you're incredibly lucky, it will be
"gripping" the paper the same amount as the tower base calibration steps. If it IS, I strongly
recommend you go buy a lottery ticket. Your luck is just that good.
If you're merely 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 paper 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 paper 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).
The concave/convex shape of the bed is controlled by the EEPROM table entry labeled
"Horizontal radius [mm]".
Fig. 22-23: Horizontal Radius Setting.
What you're going to do is bump 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 Scripts 1 through 4. 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.
Rostock MAX v2 Assembly Guide
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