In a thread grinder which grinds a thread grove on an inner surface of a workpiece while a rotation axis of a grinding wheel shaft is inclined with respect to an axis of a main shaft, a centering master which has a cylindrical outer surface is mounted to the main shaft. A measuring unit including two measuring instruments such that probes can contact two edges of a grinding wheel is mounted to the centering master. The origins of the measuring instruments are set by the probes contacting the cylindrical outer surface of the centering master. The measuring unit is moved in the axial direction of the centering master to bring the probes of the two measuring instruments into contact with the edges of the grinding wheel, respectively. The position of the grinding wheel shaft is adjusted such that measured values obtained by measuring instruments become same.

A tapping apparatus adapted for tapping a workpiece includes a lower die unit to drive the workpiece to move along a conveying direction, and an upper die unit disposed above and movable upwardly and downwardly relative to the lower die unit. A tapping mechanism is disposed between the lower and upper die units to be driven by the upper die unit for tapping the workpiece so that the workpiece is formed with a tapped hole. A thread checking mechanism is disposed between the lower and upper die units and is spaced apart from the tapping mechanism along the conveying direction. The thread checking mechanism is driven by the upper die unit for checking the tapped hole of the workpiece.

A tapping apparatus adapted for tapping a workpiece includes a lower die unit to drive the workpiece to move along a conveying direction, and an upper die unit disposed above and movable upwardly and downwardly relative to the lower die unit. A tapping mechanism is disposed between the lower and upper die units to be driven by the upper die unit for tapping the workpiece so that the workpiece is formed with a tapped hole. A thread checking mechanism is disposed between the lower and upper die units and is spaced apart from the tapping mechanism along the conveying direction. The thread checking mechanism is driven by the upper die unit for checking the tapped hole of the workpiece.

A drill and tap guide includes an elongated body having a top surface, a bottom surface, a first side, a second side, a first end, and a second end, the elongated body defining a longitudinal axis which intersects the first and second ends, and a plurality of guide holes extending perpendicularly through the elongated body between the top surface and the bottom surface, at least one of the guide holes including a central axis which intersects the longitudinal axis of the elongated body. The elongated body also includes a positioning notch formed in the bottom surface of the elongated body, where the positioning notch including two edges on opposite sides of the positing notch, the edges forming an angle with the bottom surface, and a recess between the edges, the recess being a portion of the positioning notch which is a farthest distance away from the bottom surface.

A drill and tap guide includes an elongated body having a top surface, a bottom surface, a first side, a second side, a first end, and a second end, the elongated body defining a longitudinal axis which intersects the first and second ends, and a plurality of guide holes extending perpendicularly through the elongated body between the top surface and the bottom surface, at least one of the guide holes including a central axis which intersects the longitudinal axis of the elongated body. The elongated body also includes a positioning notch formed in the bottom surface of the elongated body, where the positioning notch including two edges on opposite sides of the positing notch, the edges forming an angle with the bottom surface, and a recess between the edges, the recess being a portion of the positioning notch which is a farthest distance away from the bottom surface.