How to choose CNC turning and CNC milling? What are the differences between the two?

Among CNC lathe machining options, milling and turning are routine operations in machine shops. Both techniques use cutting tools to remove material from solid blocks to make 3D parts. Removing material is what classifies them as a subtractive manufacturing process, but there are key differences between these operations.

CNC turning is the operation of a lathe.

The name 'turning' refers to the workpiece as it rotates around a central axis. The cutting tool remains stationary and moves in and out of the workpiece for cutting. CNC turning is used to make cylindrical parts and derivatives of cylinders; imagine parts shaped like baseball bats, shafts, railings and posts.

The chuck holds the workpiece on the rotating spindle. The base holds the cutting tool so that it can move along the axis of the workpiece and enter and exit radially. Feed rate and speed are derived from the rotational speed of the part, the radial depth of cut, and the speed at which the tool moves along the axis of the part.

CNC turning operations include OD and ID cutting and grooving, boring, stepping and drilling. Since the cutting tool exerts force on the workpiece perpendicular to its axis, it is critical to support the workpiece to reduce deflection.

In CNC milling operations, on the other hand, the cutting tool rotates while the workpiece is held firmly on the table.

The cutting tool or table can be moved orthogonally in the X, Y or Z direction for cutting. CNC milling can create more complex shapes than turning. It can even produce cylindrical shapes, but to save costs, these shapes are best left to the lathe.

In a CNC milling machine, the chuck holds the tool in the rotating spindle. The tool moves relative to the workpiece to form a pattern on the workpiece surface. Feeds and speeds are calculated based on the rotational speed of the cutting tool, the diameter of the cutting tool and the number of flutes, the depth of cut, and the rate at which the cutting tool moves over the part.

The limitations of CNC milling relate to whether the tool can enter the cutting surface. Using longer and thinner tools can improve access, but these tools can deflect, resulting in poor machining tolerances, poor surface finish, and more tool wear. Some advanced milling machines have articulating heads to allow angled cuts and improved entry.

Both turning and milling operations can be used to create complex parts. The main difference is the shape of the final part. For cylindrical parts, turn. For most other parts, CNC milling works best.