Abstract: Apparatus for machining an angularly disposed array of slots (FIG. 7) concentric with the axis (85) of a bore of a valve sleeve (1) which has a sleeve holder (3) which is rotatably indexed for locating the arcuate position of each slot of the array, a cutting tool (5) positioned on the apparatus to cut a slot in the bore of the sleeve at each indexed location and a boring device (80, 81, 82, 83, 90) for forming the bore co-axially with the array of slots; the operation of the cutting tool (5) and boring device (80, 81, 82, 83, 90) taking place while the sleeve (1) is mounted in the one orientatioln in the holder (3).