CNC Toolpath Surfaces and Digital Craft

These CNC toolpath surfaces are an exploration in maximizing machine labor and minimizing handwork. An original agenda for AtFAB furniture was to get as much work as possible from the CNC router. We envisioned smooth-edged, flat plywood parts going from router bed to workbench: a scenario requiring little to no hand finishing before assembly. Many prototypes later, we learned that simple designs and profile toolpathing were only part of the equation.

Achieving those smooth, clean edges also demands good digital technique. As we continued to develop AtFAB, we began to understand the concept of digital craft. Writing our book Design for CNC gave us a chance to go in depth about digital craft in subtractive fabrication. It demands perfecting toolpaths – a combination of endmill shape, feed-rate, direction, and speed through the material. When all are optimized, the tool will flawlessly cut a material. For us, the design process is also part of digital craft. We examine what a machine does best, and design parts and objects accordingly.

Digital craftsmanship sounds like a contradiction in terms. On the one hand, digital fabrication offers labor-saving precision machining. On the other, craftsmanship demands an artisan’s labor, as well as their knowledge, careful hand, and exacting technique. CNC routing natural materials like wood saves labor, but doing it well demands knowledge and technique with design, materials, and machining.

cnc toolpath surfaces
CNC toolpath surfaces

In designing objects for CNC fabrication we are fascinated by how a design can facilitate digital craftsmanship. We saw potential in CNC toolpath surfaces for future designs, and sought to study the idea in detail. Using Fusion 360, our ShopBot Desktop CNC, and humble ¾” Douglas fir plywood blanks, we set out to develop machine finished surface techniques for future projects. Each study, combining different tool, setting, and toolpath, came right off the router and didn’t need for handwork.

With spiral clearing and several stepover and endmill combinations, we initially produced a convex contour with clear tool paths. Using a ball-nose endmill, we soon found a feed, speed, and directional combination that yielded a nearly polished contoured surface. We then developed our favorite technique, by matching our stepover dimension to our bullnose endmill. It produced a linear, fluted surface texture, which was especially luminous when machined parallel to the wood grain. Ultimately, we combined the fluting tool paths with the technique for a ‘polished’ concave surface, and have something that we’re looking forward to bringing into our designs.