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:
Additional info on my blog here:
This extruder assembly requires access to machining tools, or someone who can machine parts for you:
- The screw drive (ACME thread) has to be drilled and tapped on one end, and turned down to a diameter of 1/8" on the other.
- The coupler that attaches the flex shaft to the NEMA 17 motor really should be made of metal. It's possible to print one (perhaps out of nylon) and I may upload a printable part for this at some point.
1) Two 6mm (LM6UU) linear bearings
2) One 10mm x 4mm x 3mm (R1030ZZ) bearing
3) A length of 1/4-16 ACME threaded rod and one 1/4-16 ACME nut
4) A Dremel flex-shaft
5) A NEMA17 stepper motor
6) A ~4" long piece of 3/4" aluminum round bar stock, to turn the coupler out of
7) a 60cc luer-lock syringe
8) Various M3 bolts
9) Approximately 12" of 8mm linear shafting, cut into two pieces
1) Print the extruder lower and uppers, the plunger holder, the NEMA17 bracket, and the syringe holder.
2) Mount the ACME rod in the lathe. Center-drill and tap for M3 thread. Flip and turn about 1cm down to a diameter of 1/8". (Sorry for mixing metric and standard, but the Dremel flex shaft has a 1/8" collet, so there you go)
3) Mount the aluminum stock in the lathe; turn down to slip inside the drive end of the Dremel flex shaft. Drill a hole in the end to accept the end of the flex shaft, approximately 5/32". Drill and tap a hole perpendicular for a grub screw to hold the drive shaft. Drill the other end to about 5mm, and drill a set screw hole.
4) Snap the LM6UU bearings into the lower extruder half
5) Insert the ACME nut into the slot in the side of the extruder lower section
6) Insert the R1030ZZ bearing in the side slot of the plunger holder
7) Thread the ACME rod through the nut; slip the plunger on the end of the ACME rod, and thread a M3 bolt in to hold the plunger in place
8) Insert linear shafting into the extruder upper section
9) Zip-tie the Dremel flex shaft handle into the extruder upper section
10) Insert the linear shafing into the linear bearings; set-screws are optional, as long as the fit of the shafts is tight. Insert the reduced end of the ACME rod into the Dremel collet and tighten
11) Mount the NEMA17 to the bracket, insert the coupler onto the stepper shaft, and insert the end of the flex shaft into the other end of the coupler. Tighten all grub screws.
12) Mount the stepper bracket to your printer frame, and mount the syringe holder to your effector.
13) Insert a syringe into the extruder, and slide the whole thing into the syringe holder on the effector.
14) Calibrate your printer (steps per mm) and slicer and let 'er rip.
No special software is needed; you need to know the pitch of your drive screw, your controller microstepping value, your nozzle size, and the interior diameter of your syringe (which effectively becomes your filament diameter).
Extruder steps per mm in my case will be:
¼-16 ACME threaded rod is 1/16” per revolution, 1/16” = 1.5875mm
1/16th microstepping = 200 steps per revolution * 16 = 3200 steps per revolution
3200 steps = 1.5875mm
2015.75 steps/mm; put this value in your firmware
Using calipers, measure the inside diameter of your syringe. In my case, it's 28.85mm. In your slicer, put this value in your printer filament diameter setting.
Measure (or look up the specs) for the opening in your nozzle. I'm using a 1.5mm opening luer-loc syringe tip. Put this value in your slicer and/or printer software for the nozzle size.
That's it - start doing your test prints!