Boring machines

In a hollow rotary spindle of a boring machine provided with a pair of swing arms attached to the front end of the rotary spindle and adapted to support cutters and also provided with a driving mechanism disposed within the rotary spindle for driving the swing arm, the improvement in which said pair of swing arms extend in symmetric radial directions with respect to said rotary spindle and are rotated about the axis thereof and a pair of rams are disposed respectively within said swing arms to be movable in radial directions of said swing arm so as to extend beyond the front ends thereof, said cutters being secured at the front ends of said rams, said rotary spindle being further provided therein with a driving mechanism for driving said rams, said ram being further provided with threaded holes extending in the longitudinal direction, and said ram driving mechanism comprising an electric motor disposed within said rotary spindle, a gear mounted on a drive shaft of said motor, rotary shafts provided with rear gears meshed with said gears, bevel gears operatively connected to said rotary shafts through gearings, and screw rods secured to said bevel gears to engage with said threaded inner holes of said rams.