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After a delta calibration, make sure you save the results! I then slice a file with a large skirt of 10 or so loops, which gives me time to play with the z position before the actual object starts to print. While the skirt is printing (and ONLY when there is an active print), at the bottom of the "TUNE" menu is the "BABYSTEP" function. Adjust your babysteps so the skirt is perfect, and MAKE A NOTE of how far you had to babystep, and in what direction! Then, in the configuration menu, you can add or substract the babystep difference to the probe z offset (which is usually around -16.3 mm for a Predator). To make the nozzle closer, subtract the babystep distance from the z offset (so -16.3 becomes, say, -16.4). Make sure you SAVE the change under the configuration menu, or you will have to go through this process for each and every print. Once it's dialed in, I find that the calibration and bed leveling won't have to be re-done for many months unless I use a drastically different bed temperature, or change the nozzle.

Having the bed temperature set properly is critical, as is the cleanliness of the bed ( I wipe mine with 91% isopropyl alcohol between every print, and just recently found that my bed actually does work without tape, hairspray, etc., if I print at 60 degrees bed temp and keep the bed CLEAN). NO FINGERPRINTS! Under a microscope, the surface of the Ultrabase Pro looks like a waffle iron, and the nozzle should be just barely skimming the peaks so as to squeeze hot plastic down into the valleys. The nozzle needs to be a lot closer to the bed than the usual "sheet of paper" (0.1mm or 0.004 inch) test for the Ultrabase to do its thing.

There is actually a way to make Marlin automatically write the babystep values into itself, so as to "automagically" correct the z distance, but it gets very confusing, at least for me, to keep track of where I was and where I am currently.

I always run UBL with a heated bed, as it makes a huge difference. If you get stuck in a DEPLOY/STOW loop, it usually means that the delta height or probe z offset is wrong, and the control board is not recognizing the probing switch. This commonly happens to me when I forget to SAVE changes, and recycle the power to the printer.

Running g-code manually (I use Repetier-Host), over a USB cable, can make life a lot easier during the calibration and leveling process, and lets you issue M502 and M500 (load and save to eeprom) commands at will without having to scroll through the LCD screens.