Assembling the RepRap Extruder and RepRap Upgrades on a 3D Printer

By Kalani Kirk Hausman, Richard Horne

Part of 3D Printing For Dummies Cheat Sheet

Once the framework for a 3D printer has been assembled and the electronics selected, the final component needed is the extruder and hot-end that melt and deposit plastic to create your object. The extruder slides the plastic filament incrementally into the heated hot-end, where it pushes a small amount of the molten plastic out with each step. The extruder can be made in many ways, including:

  • Geared: Some extruders include additional gears to slow the advance of filament with each step to gain greater control, and to increase the force with which the filament can be advanced into the hot-end.

  • Hobbed: Smooth plastic filament can be held by the extruder using interlocking gears or a hobbed bolt (one with teeth cut along the axis around the bolt’s girth) to hold the filament against an idler wheel so its advance and retraction can be carefully controlled.

  • Bowden: This type of extruder forces the filament through a tube connecting the extruder and hot-end rather than forcing the filament directly into the hot-end, separating the two and allowing the hot-end to be lighter without the directly attached extruder motor for non-Cartesian formats.

  • Syringe: For designs like the Fab@Home printer or RepRaps equipped with Richard’s Universal Paste Extruder, a syringe can be used with a constrained strap to incrementally extrude paste or gel materials instead of the usual melted plastic.

  • Multi-color: Advanced extruders include multiple gearboxes and motors to advance multiple filaments into the hot end at the same time. By varying the rate of each color using additional electronics, the end result is a multi-colored print that varies throughout.

  • Dual: A common variation with more limited color mixing involves a dual extruder, which is simply two extruders side by side. This is useful for prints that include PVA (polyvinyl alcohol) or other soluble support material integrated into the same print as the object filament material.