Preparing a screw-cutting lathe for work
On a screw-cutting lathe the blank turns in a chuck while the cutting tool cuts it to shape. To prepare the lathe, the cutting tool is first fixed in the holder; its height is measured with an angle template and the overhang must not exceed one and a half times its thickness. For rough work the tool tip sits 0.5–1 mm above the workpiece axis, for hard materials 0.5–1 mm below, and for finishing exactly level with the axis. The blank is clamped in a self-centring three-jaw chuck with a special key; at school the type where the key springs out after tightening is convenient. Preparation is done only with the teacher, with the machine disconnected from the power.
Rule cards: pupils make a “allowed / not allowed” list, e.g. not allowed – stopping a spinning chuck with the hand; working with unfastened sleeves; clearing chips by hand. All work is on pictures and cards; the machine is off.