steel as it will readily adapt to irregular surfaces and still resist rupture and tearing from rough scales on the surface in operation the pressurized fluid such as compressed air is directed into fluid supply pipe 12 the air then flows through the rotary union 11 capped quick disconnect coupling 10 stator extension 9 rotating hydraulic cylinder 7 and draw tube 5 the flow of fluid from the draw tube 5 to the ambient atmosphere is through one of two alternate paths if the channel 13 through the center of brush 41 is vacant fluid flow will pass freely through this channel 13 to the atmosphere if however the portion of channel 13 through brush 41 is occupied by a workpiece 3 the brush 41 would then surround the workpiece and force the flow through the forest of fibers of brush 41 due to the variance in flow resistance between the two alternate paths the backpressure of the air adjacent brush 41 may be utilized to detect the presence of work stock at this location the brush 41 is preferably in close proximity to the work gripping members 16 of the chuck 2 in order that a minimum remnant will result it is possible however to locate the brush 41 a greater distance from this critical location with increased remnant alternatively if the machine 1 is operated by a computer numerical control system a counter may be utilized to signal the number of permissible incremental workstock advances to insure sufficient chucking stock with known incremental advances and.