Hasso-Plattner-Institut
Prof. Dr. Patrick Baudisch
  
 

springFit: Joints and Mounts that Fabricate on Any Laser-Cutter

Joints are crucial to laser cutting as they allow making three-dimensional objects; mounts are crucial because they allow embedding technical components, such as motors. Unfortunately, mounts and joints tend to fail when trying to fabricate a model on a different laser cutter or from a different material. The reason for this lies in the way mounts and joints hold objects in place, which is by forcing them into slightly smaller openings. Such “press fit” mechanisms unfortunately are susceptible to the small changes in diameter that occur when switching to a machine that removes more or less material (“kerf”), as well as to changes in stiffness, as they occur when switching to a different material.

We present a software tool called springFit that resolves this problem by replacing the problematic press fit-based mounts and joints with what we call cantileverbased mounts and joints. A cantilever spring is simply a long thin piece of material that pushes against the object to be held. Unlike press fits, cantilever springs are robust against variations in kerf and material; they can even handle very high variations, simply by using longer springs. SpringFit converts models in the form of 2D cutting plans by replacing all contained mounts, notch joints, finger joints, and t-joints.

(a) This model downloaded from the Internet does not assemble properly, because the user’s laser cutter has removed less material (aka smaller “kerf”) than the machine this model was designed for. Similar issues occur as a result of larger kerf and when switching to a different material. (b) SpringFit tackles this by replacing traditional (press-fitbased) mounts and joints with what we call “cantilever-based” joints and mounts. (c) Processing the model using springFit before laser cutting resolves the problems and it can now be assembled properly.

A press fit mount carefully tuned by an engineer for his laser/material fails when fabricated on different equipment. (a) On machines with smaller kerf, it cannot be inserted completely. (b) On machines with wider kerf, it is loose and falls out. (c) When cut from brittle material, it breaks the model.

The use of cantilever-based mounts and joints allows one and the same models to fabricate reliably (a) on machines with small kerf, (b) with wide kerf (here simulated by eroding the model by 0.2mm), and (c) different material, and (d) even slightly different sized buttons (this one is 0.3mm bigger in diameter).

Cantilever spring versions of (a) finger joints and (b) how they assemble. (c,d) notch joints or cross joints and (e,f) T-joints.

Publication

Thijs Roumen, Jotaro Shigeyama, Julius Cosmo Romeo Rudolph, Felix Grzelka, and Patrick Baudisch
springFit: Joints and Mounts that Fabricate on Any Laser-Cutter 
To be published in Proceedings of UIST'19 . 
Paper PDF | talk (coming) | code (coming)