The flat surface where an object is built is called the bed, and how well the first layer sticks to this build plate, known as bed adhesion, is one of the most critical factors in print success. Heated beds maintain a stable temperature that improves adhesion and reduces warping, especially with materials like ABS. Common bed surfaces include polyetherimide (PEI) sheets, which are popular for their reliable grip, and glass beds, which provide a smooth, flat surface and produce glossy bottoms on finished parts. The maximum size of an object a printer can produce is its build volume, with typical hobby printers offering around 200 to 300 millimeters in each axis.
The mechanism that feeds and melts filament is the extruder, which terminates in the hot end, a heated nozzle assembly. The nozzle is the small orifice through which melted plastic exits, and the standard size is 0.4 mm, with smaller diameters chosen for fine detail and larger ones for faster, thicker extrusion. There are two main extruder layouts: a Bowden extruder places the motor away from the hot end and pushes filament through a guide tube, keeping the moving print head light and fast, while a direct drive extruder mounts the motor on the print head itself, which gives better control with flexible filaments like TPU. Periodic maintenance with the cold pulling technique, which involves heating and then pulling filament through the hot end at a lower temperature, helps keep the melt zone clean of residue.