Abstract: In a rotary shear line in which sheet stock is fed by a feeder to a rotary shear for fly cutting by its rotating cutting edges, a synchronous speed and a synchronization length are calculated by an arithmetic unit which are supplied with the cutting length and the average feed rate of the sheet stock. Reference pulses of a frequency corresponding to the synchronous speed and the synchronization length are provided to a first numerical controller for controlling the feeder and a second numerical controller for controlling the rotary shear. The first numerical controller controls the feeder to feed the sheet stock at a speed higher or lower than the synchronous speed in such a manner that when the sheet stock is fed at the synchronous speed, the length of the sheet stock short or excessive of the cutting length before its cutting is compensated for within a cutting period.

Abstract: A first base supporting a lower blade is reciprocated horizontally by rotation of a first motor in one direction only. A second base supporting supporting an upper blade is reciprocated vertically by rotation of a second motor in one direction only. A signal corresponding to the movement of said work, preset length data and a signal corresponding to the rotation of said first motor are fed to first base numerical control means, and the first base is controlled during forward run of the first base by the first base numerical control means such as to follow the running of the work with the work projected by the preset length from the first base.