While bits of plastic are the usual material for 3D printers, there are hundreds of other materials that are equally well suited for 3D printing. One of the most famous is chocolate, a material so popular and easy to manipulate inside an extruder there are even Kickstarters for 3D printed chocolate bars.
There are many more materials deserving of being 3D printed, though: wax for lost wax castings, other foodstuffs for improbably shaped edibles, and ceramics so I can finally print a life-sized, functional version of the Utah Teapot.
Unfortunately, for all the progress of plastic extrusion, little has been done about extruding pastes, foods, and clay with a 3D printer. The RepRap paste extrusion working group is fairly close to being dead, so let this volume of 3D Printering explore what has been done in the world of paste printing.
Hey, remember when MakerBot was innovative?
One of the first instances where paste extrusion was demonstrated to the world was – remarkably – with the MakerBot Frostruder. While the Frostruder MK1 was never made available for sale, The Frostruder MK2 was available for a short period of time. The mechanics behind this extruder meant for frosting cupcakes – both the cake and the machine – are actually pretty clever. A syringe is filled up with some sort of paste, and an air compressor to supply pressure. One solenoid valve opens to dispense frosting, and another serves as a relief valve to stop the extruder from oozing. It’s a brilliant solution to a problem, an ingenious device, and not for sale on the MakerBot store anymore.
Interestingly, Makerbot’s Frostruder MK1 used a stepper motor/plunger setup. This was an inherently flawed design, as a syringe plunger will have massive start and stop times. Whether through ignorance or animus, some parts of the 3D printing community have ignored the success of a Makerbot product, and some work has continued on a stepper driven plunger design.
So plungers are out, what’s in?
The name of game in paste extruders now is a pressure-based system. A very clever design is the SupportExtruder, an odd design that looks more like someone having fun with water rockets than an actual machine.
The SupportExtruder basically consists of two parts – a pressure vessel, basically a water bottle and a balloon, and a solenoid to let pressurized air into the bottle. When the solenoid activates, a bit of compressed air is allowed into the bottle. This compresses the balloon containing any sort of paste which travels down to the nozzle and onto the build platform. A clever device that’s actually been used successfully. In fact, with a little ingenuity, this water bottle could serve as a hot water bath for molten edibles such as chocolate.
The problem with pressure
With both piston and pressure-based extruders, there is one drawback: it’s impossible to have a true continuous feed system. Eventually, after decorating a whole lot of cakes or extruding a whole lot of chocolate, you’ll have to tear down your extruder and refill it.
One solution to this is using pumps. Peristaltic pumps - basically a flexible tube with a set of rollers pushing a fluid along – could be used for thinner liquids, but for clay and ceramics this method has been met with failure. A much more interesting way of feeding thick liquids onto a build platform is a progressive cavity pump.
The progressive cavity pump looks something like an Archimedean screw that fell into the hands of Dali. Designed by Rene Moineau in the 1930s, it consists of a helical rotor (the spinny bit) and stator (the part that contains the spinny bit). The rotor and stator (as seen to the right) have slight gaps between them that can pump a fluid from one place to another. In fact, this sort of pump is often used in the manufacture of food, sewage pumping and even pumping cement. Sounds a lot like what a true ceramic extruder should do, huh?
Surprisingly, there hasn’t been much progress in the development of a progressive cavity or Moineau pump for 3D printers. A shame, because these are the perfect pumps for dispensing thick liquids but commercial offerings are both huge and expensive. Nevertheless, a few people over on Thingiverse have made their own Moineau extruders with varying degrees of success.
What happens next with these Moineau extruders is anyone’s guess, but with the availability of flexible PLA and harder, slippery materials such as nylon, the possibilities of continuous extrusion of paste are expanding every week.
One final note:
Last week I put out a call for more topics for this column. I thank all of you that sent in your thoughts, and I’ll get some stickers out to you shortly.
A number of you said you hated the name “3D Printering”. I’ll admit I hate it too, so I guess it’s time to change it. Two of the best suggestions IMHO are, “Printicles” and “Printerest”. Printerest is an absurdly clever name for a 3D printing column, but I’ll defer to your judgement in the comments.