Preassembled ball-joint chain

by sylefeb, published

Preassembled ball-joint chain by sylefeb Mar 3, 2013
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This is a chain of ball joints that are printed preassembled. It comes as an open chain or as a closed loop.

Print, and enjoy!


The chain is made of ball joints that are printed pre-assembled. You will likely need to apply some force to break them free. The inner spheres are actually slightly deformed so that you can lock the joints in the chosen positions. If a joint does not lock, rotate it around the connector axis - it should become stiffer at some angles. Make sure your plate is properly leveled to avoid the outer and inner spheres to bond on the first layer: this happens if too much plastic is poured due to the plate being too close to the nozzle.

The provided 'csg' files can be imported with OpenSCAD and rendered into a stl - both contain 12 ball joints. The result is shown by the image rendered with transparency. This is a parametric model created with my own software. I will release the software soon (still working on it) but I include the script for reference - should be easy to convert to OpenSCAD.

Several assemblies are possible:

  • balljoint_chain.csg is an open chain
  • balljoint_cycle.csg is a closed loop

I provide stl files for the chain and loop of 8 joints (for some reason OpenSCAD has trouble with the 12 joints version on my computer). I also included gcode of the 12 joints version for my Replicator 1 -- use at your own risk (afaik the code may not work on a different printer).

I printed it in ABS, at 0.2mm layer thickness, 120 mm/s travel and 60 mm/sec print speed. These are the settings used in the provided gcode.

Have fun!

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That looks great, what tolerance between inner and outer sphere did you aim for when designing?

Thanks - I believe the tolerance is 0.2 mm - but that is not everywhere the same as the inner spheres have protrusions to 'grip' on the outer hull. The file 'balljoint.lua' contains the full code with measures in millimeters.

Awesome, glad to see more preassembled things. Just out of curiosity, it seems like you could make this easily in OpenSCAD; what is different about your software?

Thanks Emmett! OpenSCAD is great, and you could definitely model this directly with it. My software actually started as a slicer: I got interested in RepRaps, and wanted to understand the process better. Then I realized that you could skip entirely the STL mesh generation by directly slicing the CSG -- this idea is not really novel; it's included in RepRap Host I think ( see http://blog.reprap.org/2011/10/say-goodbye-to-unsightly-stl-triangle.htmlhttp://blog.reprap.org/2011/10... ). My software simply goes a bit further with it, supports meshes as input and uses 'GPU tricks' to make it very fast. For instance, it only takes around 5 minutes to slice this model on my computer (and there is no STL generation - so that's 5 minutes to printing). However, that requires a big NVidia GPU (>= GTX 480). This is definitely not a competitor for OpenSCAD which generates meshes (mine can only slice), this is why there is a button to export the CSG tree and load it in OpenSCAD :).

Cool. I played around with writing my own slicer awhile back too; no easy task.

Just wanted to point out that the software I developed is now available: http://webloria.loria.fr/~slefebvr/icesl/http://webloria.loria.fr/~slef...
Have fun :)

You might want to mention on your site that it is a Windows-only application. While GPU requirements are listed, OS requirements are nowhere to be found and a lot of us RepRappers (and software developers for such) use Linux as our primary OS. As it looks like your app is written in Lua, you may be able to make it multiplatform easily if you use standard OpenGL shaders. It looks promising and I very much look forward to a Linux release =)

That is a good point - I'll update the description on the website. In fact, a Linux version is on its way, and I was hoping to make it available faster. The app is in C/C++ but uses Lua for modeling language.