Greetings,
We wanted to briefly put together a list of things we learned about printing joints during this project to produce a moveable Bucky model. Read below to learn about what parameters to consider when you print joints.
Printing Parameters (Ultimaker 3):
Print Material – PLA
Support Material – PVA
Layer Height – 0.1 mm
Infill Density – 25%
Number of Shells – 2
Joint Gap – 0.2 mm
The layer height is critical to printing clean joints. We wanted to use the finest layer height our printer could achieve. Since the joint gaps need to be small for a tight fit, the layer height needs to be small to avoid fusing the ball and socket together.
Number of shells also plays into this since the sockets are 3D shapes. The side dimensions of the socket are directly related to the number of shells and the nozzle diameter, not the layer height. Since we had a nozzle diameter of 0.4 mm, two shells produced a width of 0.8mm. Our slicing software, Cura, attempts to place the outermost shell at your STL’s defined dimension, but we found there is some expansion when multiple shells are printed adjacent to each other. We initially wanted to use a single shell to better control our outer dimensions, but this left our part with reduced strength. This could be compensated for by increasing infill density, but with resulting consequences in increased print time. We thought looser joints were an acceptable trade for a reasonable build time.
Joint gap is the gap between the outer surface of the ball and socket in the ball-and-socket joint. This is clearly an important parameter for quality joints. A joint gap that is too small will result in the parts being fused together during printing. Too large of a joint gap will produce sloppy joints. We found a gap of 0.2 mm to be the right size. Unfortunately this requires a little trial and error to pin down depending on your part and printer. A good place to start may be 0.3 mm and work down from there.
The part gap we defined as the gap between appendages and the torso of Bucky outside of the joint. Similar to the joint gap, you need to put a large enough gap so the parts done fuse together at their interface. We used 0.2 mm again for this gap and saw good results.
We found that removing the priming tower improved our print quality and print time for this type of model. Since all of the soluble support is on the bottom of the model, the PVA and PLA are rarely used on the same layer. The only exception to this is part of the elbow and foot. We didn’t have any issues with the two materials being placed incorrectly without priming. The print time was reduced by approximately 1 hour since the printer didn’t have to travel over to the corner and print the tower.
We really enjoyed this project and were surprised with the level of difficulty in modeling good joints. We focused mostly on the printing parameters, but the first step is designing a good, printable joint. Hopefully you found our blog informative.
? Click me ?
Time to celebrate!
Team Bucky