When this machine runs, it jogs its X, Y and Z axes under pendant control while ball screws and linear guide rails move the motion system over a black granite surface plate. It is a scratch-built milling machine, released as an open-source design called the RIG CNC, and it came in under $1500 despite weighing a few hundred pounds.
The construction approach is what stands out to me. The maker combined affordable precision stock: a granite surface plate for the base, a precision-ground steel column, OpenBuilds C-beam extrusions flanked by 20x20 extrusions for the frame, and printed plastic parts tying the granite and steel together into a mill shape. The whole machine was designed in CAD first, and the philosophy is that printed parts can later be swapped for aluminum ones the machine cuts itself. Several structural connection plates and motor mount housings are printed in black and white filament, and the spindle head is a red cast iron casting with an R8 collet taper, driven by a belt-driven brushless DC motor on a ZM-6615 driver module. An OpenBuilds BlackBox runs the show, with a handheld Interface pendant for control, and the work sits on an aluminum T-slot bed.
One clever detail: instead of drilling into the granite, a plate attaches the table to the stone. The maker admitted drilling accurately through granite in several spots was not something they felt able to do, and while flipping the whole machine to remove the XY assembly seemed dangerous, the plate was easier to handle even if it is suboptimal.
Still open: the best way to release the CAD files, and plans to measure deflection and spring constants under load to compare printed and aluminum plates. A dial indicator on a magnetic base rests on the granite, and a machined aluminum test piece sits bolted beside cutting fluid.
Project by Ryan A. Kelly. Watch it on their YouTube channel: