plate 33 and tube 30 with associated elements relative to the sector plate 31 the two split bearings 28 and 29 are adjustable at 62 to exert any desired degree of drag on the rotary tube 30 the relative directions of rotation of the dado blades 48 are indicated by arrows in fig1 during cutting of a workpiece 51 this rotation directs sawdust in an air current rearwardly through the bore of the tube 30 so as to expel the sawdust at the rear end of the machine the entire carriage 22 with the two cutter heads and their motors is reciprocated at proper times on the horizontal rails 21 by operation of a longitudinal cylinder piston actuator 63 whose piston rod 64 extends rearwardly of a cylinder 65 of the actuator and is coupled as at 66 to a stationary member 67 on the rear end of the machine base above the rails 21 a spring loaded bumper pin 68 is provided on the machine base in the path of movement of the rear cross bar 25 to cushion the carriage at the rearward end of its travel the forward end of cylinder 65 is coupled at 69 to the rear of sector plate 31 which as noted is rigid with the carriage structure in the advancement and retraction of the carriage 22 therefore it is the cylinder 65 which travels in relation to the piston rod 64 which is stationary during its reciprocation on the rails 21 the pairs of rollers 23 prevent vertical displacement of the carriage 22 simultaneously the carriage is laterally restrained and guided by a cylindrical longitudinal guide bar 70 fixedly held in pillow blocks 71 attached to.