How Are Curved Surfaces Milled?

Curved surfaces can be milled in several ways. Selection depends on part shape and size, production quantity, accuracy requirements, and available equipment. For a small, thin part in one-off production, the profile may be laid out and milled manually. High-accuracy parts or batch production can use CNC or copy milling machines.

Template-Guided Curved-Surface Milling

Template-guided milling feeds the cutter along the contour of a template that is identical or similar to the workpiece shape. The template-to-workpiece scale can be 1:1 or greater than 1:1. A template larger than the workpiece generally produces higher profile accuracy; a smaller ratio produces lower accuracy.

1. Manual template milling. The template and workpiece are clamped together, and the cutter shank remains against the template while conventional milling is used. To fine-adjust workpiece size and compensate for reduced cutter diameter after regrinding, both the cutter shank and template are tapered by 20°-30°. Surface roughness Ra can reach 6.3 μm. The method suits small-batch production.
   
2. Rotary template milling. A rotary template attachment can machine a curved groove on a vertical mill. As the rotary table turns, a counterweight moves the slide to the right and keeps the sleeve against the template. Combined table rotation and lateral slide motion guide the cutter around the workpiece profile. The mechanism is simple and compact, but the cutter has a long overhang and may bend, reducing accuracy. It suits batch production. The cutter arbor does not carry the counterweight force.
   

Copy Milling Curved Surfaces

In copy milling, a copy milling machine automatically forms the workpiece surface to match a template. Ball-end mills are used primarily. The method is suited to molds with complex three-dimensional surfaces or to lower-accuracy workpieces that cannot be produced by other methods. Copy milling machines may be one-directional, two-directional, or three-directional.