A three-dimensional printer uses its extruder and build platform to properly orient the build platform within a working volume. In a multi-point leveling operation, the extruder is moved to the z-axis origin at a number of x-y positions within the plane of the build platform, and the height of the build platform is adjusted to meet the extruder at the origin. If the build platform is a meltable material such as a plastic, then this leveling process must be performed while the extruder is cool. A homing operation may be performed periodically after leveling in order to realign the z-axis positions of the build platform and extruder. A non-meltable contact point may be usefully provided so that homing can be performed while the extruder is hot, such as immediately before a build or between a number of builds.