The first layer of a print must be printed at the right height, to within perhaps 50 microns, everywhere across the print bed, to ensure that the print sticks to the bed and the nozzle doesn't crash into it. For a Cartesian printer this may be as simple as ensuring that the bed is level, but a delta printer has a number of additional parameters to adjust. Even if your printer is well calibrated and unchanging, a high-quality Z probe may be more repeatable than your endstop. It is often useful to run a quick autoprobe before every print (and not re-home afterwards). Setting up such an autoprobe requires a certain amount of configuration.
For a comparison of advantages and disadvantages for various Z probe options see Choosing a Z probe.
See Connecting a Z probe for details on the electrical connections.
RepRapFirmware supports two different types of Z probing:
Running the G32 command causes the firmware to execute macro file /sys/bed.g. This macro normally uses G30 commands to define the probe points individually, including an optional Z probe trigger height adjustment for each point, and probe the bed, then:
In some cases you may want to combine bed plane levelling with manual correction of bed levelling screws.
Mesh bed compensation allows the printer to adjust the nozzle height during printing to compensate for an uneven bed or for sag in the gantry.
G29 probing uses a grid of points defined by its size and the spacing between points. You can probe a large number of points without having to define their coordinates individually. It is only used for mesh bed compensation.
On a Delta printer, you can if you wish use G32 to perform auto calibration followed by G29 to compensate for any residual bed height errors.
On a Cartesian or CoreXY printer you can use G32 bed probing for Bed levelling using multiple independent Z motors, followed by G29 probing to do bed compensation.
For full details, see Using mesh bed compensation