4- Calibrate the firmware to print to correct dimensions.
At this point the printer probably prints, but the results are dimensionally wrong. Printing something 100mm long results in a printed object that is not exactly 100 mm long. This also, can be corrected in firmware. Adjustments to DELTA_DIAGONAL_ROD in the firmware control the size of the printed object.
Create a simple calibration object in openscad, slice it, and print it. By measuring the actual size of the object as printed and comparing it to the size in the design, the accuracy of the printer can be assessed and adjusted.
Here is my sample openscad object:
If the length of the object is wrong, adjust DELTA_DIAGONAL_ROD:
new DELTA_DIAGONAL_ROD =
100 / measured_length * original DELTA_DIAGONAL_ROD
then re-upload the firmware, and print and measure again. When the printed object measures 100 mm, the printer is printing accurately to size and is fully calibrated
And so what if, in the end, the length of DELTA_DIAGONAL_ROD in the firmware doesn't match the length of the rods that were built?
Anyway this process seems to work for me. Good luck!