Improvements in machines for cutting passages through rock

910,882. Mineral-mining machines. DISTINGTON ENGINEERING CO. Ltd. Jan. 12, 1959 [Oct. 12, 1957], No. 28798/57. Class 68 (1). A mineral-mining machine has two toolholders 6, 7 swinging in unison about parallel axes in a plane at right-angles to the direction of advance of the machine and the cutting tools 12, 14 are so mounted on the holders that they are retracted a short distance towards the holders between the cutting stroke and the idle return stroke of the holders. The tools are moved in and out of the holders by hydraulic, double-acting jacks acting on bell-crank lever systems housed in the holders and connected by ball joints to the tools. Each holder is secured to the outside of the moving part or outer cylinder of a rotary engine, the fixed part or shaft 4 of which is secured between the side plates 2 of the body of the machine. In the ends of these shafts are positioned axially of the shafts hydraulic jacks 44, 45 that are used to secure the head to the sides of the excavation being formed. The machine is advanced with a step-by-step motion due to jacks 50 acting between a shaft extending parallel and between the other shafts and an abutment plate 53 having a limited sliding movement in the machine. By appropriate setting of the first mentioned jacks the machine can be rocked forward by the last-mentioned jack about each shaft alternately.