This DIY CNC Mill Is Impressive

The most important quality of a milling machine is rigidity. Material science being what it is, the best way to achieve suitable rigidity is with a lot of material. The industrial mill in my garage, for example, is about 3,000 pounds of mostly cast iron — it weighs more than many small cars. That isn’t cheap and isn’t easy to DIY, which puts mills (both CNC and manual) capable of handling metal out of reach of most hobbyists. But Cody Lammer had both dedication and a healthy budget, which let him build this very impressive DIY CNC mill.

Rigidity is important because any flex between the end mill and the work piece will result in imprecision, chatter, poor surface finish, and broken tools. There is a lot going on between the end mill and work piece, including at least three moving axes, so it is important that the frame resist flex as much as possible. For that reason, most manufacturers make frames out of cast iron. It is heavy, sturdy, and relatively inexpensive.

But casting iron is very difficult — far outside the capability of even the most well-equipped hobbyists. So, Lammer built his CNC mill by starting with a base of poured epoxy granite surrounded by a frame made of 8020 aluminum extrusion. This is the second version of the mill and Lammer used the original to fabricate many of the parts used for the build.

This is a moving-gantry design, with the work piece remaining stationary while the machine moves in all three axes above it. The gantry rides on linear rails, with ball screws and accompanying nuts.

Manual mills tend to use more affordable acme or trapezoidal lead screws, because the machinist can compensate for backlash as they’re milling. CNC mills struggle with that compensation and so ball screws are preferable, as they eliminate almost all backlash.

Closed-loop NEMA 23 stepper motors turn the ball screws and the closed-loop feedback helps them compensate for any skipped steps. An MKS TinyBee running FluidNC software controls the steppers, receiving g-code from a single-board computer with Universal G-Code Sender software. The mill has an ER20 spindle driven by a 6473 brushless DC motor intended for use with electric skateboards.

With the sturdy epoxy granite base, the machine weighs in at more than 400 pounds — very light by industrial standards, but very heavy by hobbyist “desktop” CNC mill standards. It has 12” of travel in the X axis, 24” of travel in Y, and 3.8” of travel in Z, which is very generous. An enclosure keeps all the chips inside and will be very useful if Lammer decides to add a coolant system. There is even a nifty pendant on the machine that looks really nice.

Lammer will demonstrate the mill in a future video. But the original seemed quite capable when milling aluminum and the new version should be even better.