We have long been fascinated by CNC flip milling. It is a common technique for overcoming the limits of 3-axis CNC routers that cannot perform undercuts. Just as it sounds, the process involves milling Side A, flipping your stock over, and then milling Side B. By giving the endmill access to multiple sides of the stock, one can achieve a wider range of shapes and geometries than simple profiles, contours, and pockets. The latitude this gives designers and makers is compelling!

While the concept of CNC flip milling is simple, achieving it is fraught with challenges. Reconciling the precision of digital fabrication and the inherently analog process of flipping isn’t easy. Toolpath alignment from Side A to Side B is only as precise as the human maker. After milling Side A, and turning over the stock, that maker must precisely re-align the stock on the router bed. Only then will the Side B toolpaths align with those already cut on Side A. Even the most exacting human maker may fall short of the robot’s perfection.

Up until now, our projects prioritized simplicity as a means of achieving repeatable, digital technique. Repeatability is what enables a global, distributed network of local fabricators to match the work of centralized factory. So, for AtFAB furniture, we stuck to profile cutting and basic fabrication technique. And, while we introduced some complex fabrication concepts in our book Design for CNC, we found them too advanced for the projects.

As we research new designs, we’re exploring ways to achieve complex digital fabrication technique, with the intuitive ease and attainable digital craftsmanship of our earlier projects. Using Fusion 360 and our Shopbot, we are seeking repeatability, with complex methods like flip milling, toolpath surfaces, and parametric design.

We channeled our explorations in flip milling with these interlocking discs and rings that  form a stack. The stack serves as a test, fabrication prototype, and sampler of edges, details, and joinery. We’ll shape future designs around the successful outcomes. Every element in the stack has a pocketed top and bottom, and beveled outer profile. The base and top discs have contoured surfaces. We leave each part unfinished, so we can evaluate the effects of our toolpath settings.