A system produces orthodontic aligners by CNC machining. A digital model of the patient's dental anatomy (26) is manipulated using CAD software (22) to create a solid CAD model (30) of an aligner. A CNC milling machine (28) is then used to machine the inside (42) and outside surfaces of the aligner (70) from a block (40) of suitable material. A progressive series of aligners can also be designed.