Stepper-driven paste extruder for Delta-type printers

This is a stepper-driven paste extruder for delta-type printers, specifically the Rostock Mini. It is the result of a collaborative project at Port City Makerspace in Portsmouth, New Hampshire to build a 3D printer that prints using chocolate. It was heavily inspired by the ceramics/clay extrusion work of Jonathan Keep, though we have since moved away from his pneumatic extruder design.

There are many paste extruder designs out there already. Although some of them reportedly work pretty well, none of them seemed ideal for our use. The goal of extruding chocolate - the kind that hardens, not frosting or ganache - presented some unique technical challenges, especially keeping the material hot while extruding. This would make extrusion over a tube difficult (for temperature control reasons). We also wanted to avoid mounting the stepper motor on the effector, to keep the weight lower, since we were using a delta.

The result is a flex-shaft driven extruder. It is precisely controllable without any special software. Since it is driven by a stepper, you can simply calculate the steps-per-mm of the screw drive, plug the inner diameter of the syringe into your slicer as the filament diameter, and everything will work.

There are still some issues to address:

• We reduced effector weight and gained precise control over extruded volume with the screw design, but any inaccuracy in terms of runout in the screw drive leads to a lot of friction which can give you stuttering movement of the plunger.
• There can be a lot of friction with the syringe plunger in general.
• Managing the springy-ness of the flex shaft is a challenge at times.
• You are limited in print speed (well, extrusion speed) by the viscosity of the material you are extruding. Chocolate, for example, is very thick and the extruder motor will stall if you try to print quickly and force material through the nozzle too fast.

Please note that some of the pictures above are of a previous revision of the parts; the downloadable files and their renderings are current, however.

Video of a print from this extruder is available here:
https://www.youtube.com/watch?v=cwZJkWkvtpE

Additional info on my blog here:
http://gunnenginerding.blogspot.com/2015/06/stepper-driven-paste-extruder-for-delta.html