CNC Chisel

Out of all materials, only a narrow subset are machinable by traditional machining tools. A machinable material needs to have properties that lie in a very specific range. The material must be sufficiently ductile to be cut by the machining tool, yet not too hard to wear the tool down. This requirement for ductility eliminates a large number of brittle materials, and we wish to explore the possibility of shaping these materials in a controlled way.

Traditional machining uses rotating cutting tools in order to shape the material. A cutting tool cannot easily be used when shaping brittle materials. Brittle materials tend to fracture when a high speed, hard material impacts them. Thus, almost all brittle materials are shaped using abrasive techniques. Abrasive removal of material is a slow and arduous process, and is not effective at quickly removing material. Jeremy Garcia and I explored the possibility of using the fracturing properties of brittle materials to our advantage. We implemented a computer controlled impact-based machining process which repeatedly uses a hardened tool to impact a brittle material at high speeds and impact forces in order to fracture the material in a controlled way to remove material for shaping.

CNC Chisel with protective covering removed

The goal of this process was to develop a method to quickly remove large amounts of a brittle material, which could later be shaped more precisely by abrasive techniques. Such a method would have large impact on our ability to shape many commonly used materials, such as the stone, concrete, and glass. Each material should be evaluated on a case-by-case basis, as fracture occurs differently in materials with different microscopic structures.

Custom CAM software GUI interface

In order to test this method, we designed and built an automatic chisel that we mounted on the end of a 6 degree-of-freedom robotic arm. We built our own slicer and computer-aided machining software in order to generate tool-paths for our chisel, since no existing software existed for such a system. We also then evaluated machining plaster as a general analog for stone and other brittle materials, but all of our observations may not transfer perfectly.

Resulting test piece with fracturing occuring