Thingiverse user Tony Buser has recently made a very cool Hilbert Cube using a MakerBot Thing-o-Matic with dual mk7 extruders. The Hilbert Cube was printed all at once as one piece. The success of printing such a complex object was based on his earlier project dissolvable support gearbox. It has gears on shafts inside a shell and would require internal support structures but very difficult to remove. Buser found a solution: he tried to printing with a water soluble plastic and a base plastic simultaneously. At the beginning he used ABS and PVA plastic but he had trouble getting PVA to stick to ABS. However when he switched the ABS to PLA it sticked pretty well with PVA when he extruded both at around 210C.
Let's read what PVA is. According Makerbot's wiki:
Poly-vinyl alcohol (PVA) is a low temperature thermoplastic with the interesting property of being soluble in water. PVA dissolves rapidly with simple submersion. A 10cm cube printed with no one surface at 20% infill and submerged in one cup of room-temperature water will begin to break apart within 20 minutes, and entirely within 24 hours. To speed up the dissolution, gentle stirring can be applied. Warm water may also enhance the process. The water will quickly become an opaque white, and take on the appearance and consistency of wood glue.
PVA is odorless and nontoxic and also resistant to oil, grease and solvents. Buser took advantage of PVA's ability to dissolve in water and made it as water soluble support for his design. The gearbox was created at once using PVA for support and PLA for the model at 0.3 layer height, both extruded at 210c and HBP set to 40c on blue painters tape.
The photos below shows what the dissolvable support gearbox looks like after 12 hours in warm water.
So, the PVA melted away and the gear worked and could be turned freely. A successful test! Buser has uploaded the .stl file on Thingiverse so feel free to download and do the experiment yourself. More photos and video of the Buser's test are available here.
image courtesy of Tony Buser
Posted in 3D Printing Technology
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