For printers with ATmega 2560 processors, Sailfish provides support for auto-leveling.5 Auto-leveling performs on-the-fly adjustments of the printing commands, moving each layer of the print into a plane parallel to the build plate. This accounts for any slight tilt of your build plate, producing better adhesion of the print’s first layer and avoiding other leveling-related difficulties. However, auto-leveling cannot correct for a seriously warped build plate.
The careful reader will realize that there are an infinite number of planes parallel to the build plate. By knowing the fixed Z position of the extruder nozzle when the Z probe is triggered, the firmware knows the exact plane to use for each print layer and can even adjust the initial printing gap between the build plate and extruder nozzle. This piece of positioning information is a printer calibration which can be done once at the factory for you and saved in the printer’s memory. With Sailfish, it is saved as the Z home offset. Like the traditional use of the Z home offset, you can adjust it to fine tune the initial printing gap: increase the value to decrease the size of the gap; decrease the value to increase the gap. However, the Z home offset no longer has 0 mm as its typical value. Its typical value is now a design parameter of your printer. Consult your printer’s documentation for information on the typical value and how to recalibrate it should you need to.6
The process of auto-leveling begins with your slicing profile’s initial print commands. These commands, described in Section 9.7, will probe the height of three locations over your build plate and then tell the printer to activate auto-leveling. Once the print is finished, auto-leveling is turned off: it does not remain on for subsequent prints, even if you use the “Print Another” feature (Section 3.5). Each print which will use auto-leveling must have the necessary commands at the start of the print. Inclusion of these commands is done automatically for you by your slicing profile. Note that auto-leveling may be used when printing over USB or from an SD card.
To “disable” auto-leveling, simply remove the auto-leveling gcode commands from your print file. But when you print without auto-leveling, you need to consider your slicing profiles and whether they include commands to recall the Z home offset (M132 Z). If they do, then give thought to either removing the Z axis from those commands or saving your current settings in a Sailfish profile (Section 3.7.9) for later recall and then setting the Z home offset to 0 mm for use with non-auto-leveling slicing profiles.
5An ATmega 2560 processor provides the necessary memory for additional firmware features. The smaller ATmega 1280 processors used in genuine MakerBot printers and early clones lack sufficient memory.
6For a ZYYX printer whose probe is triggered by contact with the build plate at Z=0 mm, this fixed position is the distance between the extruder nozzle and probe tip expressed as a negative value. That is, if the distance between the probe tip and extruder nozzle is 1.0 mm, then when the probe contacts the build plate at Z=0 mm, the extruder nozzle is below the build plate at Z=-1.0 mm. Thus, the Z home offset is set to -1.0 mm. If you instead use a build plate with raised sections 3.0 mm in height that the probe contacts, and the extruder is 1.0 mm below the probe tip, then the Z home offset would be set to 2.0 mm: when the probe tip contacts the raised section at Z=3.0 mm, the extruder is 1.0 mm lower and thus at Z=2.0 mm.