3D Printed CNC Knee Mill

Nov 09, 2023

CNC mills will never match real heavy metal mills on hard materials, but that won't stop people from pushing the limits of these DIY machines. One of the usual suspects, [Ivan Miranda] is at it again, this time building a knee mill from aluminum extrusions and 3D printed fittings. (Video after the break.)

Most DIY CNC milling machines we see use a gantry arrangement, where the bed is fixed while everything else moves around it. On most commercial metal milling machines, the table is the moving part, and are known as knee mills. In the case of [Ivan]'s mill, the table can move 187 mm on the X-axis and 163 mm on the Y-axis. The 1.5 kW spindle can move 87 mm in the Z-axis. All axes slide on linear rails and are driven by large stepper motors using ball screws. The table can also be adjusted in the Z-direction to accept larger workpieces, and the spindle can be tilted to mill at an angle.

To machine metal as [Ivan] intended, rigidity is the name of the game, and 3D printed parts and aluminum extrusion will never be as rigid as heavy blocks of steel. He says claims that the wobble seen on the video is due to the uneven table on which the mill was standing. Of course, a wobbly base won't be doing him any favors. [Ivan] also had some trouble with earthing on the spindle. He nearly set his workshop on fire when he didn't notice tiny sparks between the cutter and aluminum workpiece while he was cooling it with isopropyl alcohol. This was solved with the addition of the grounding wire.

While the machine does have limitations, it does look like it can machine functional metal parts. It could even machine metal upgrades for its 3D printed components. One possible way to improve rigidity would be to cast the frame in concrete. [Ivan] has built several other workshop tools, including a massive 3D printer and a camera crane.