SCHEDULE I 49 Dry grinding of metals or articles of metal applied by hand to revolving wheel or disc driven by mechanical power. Turning (external or internal) of non-ferrous metals or of cast iron or articles of such metals or such iron where the work is done dry, other than a precision turning where the use of goggles or a screen would seriously interfere with the work or turning by means of hand tools. Welding or cutting of metals by means of an electric oxyacetylene or similar process. The following processes when carried on by means of hand tools or other portable tools: Fettling of metal involving the removal of metal. Cutting out or cutting off cold rivets or bolts from boilers or other plant, or from ships.- Chipping or scaling of boilers or ships plates. Breaking or dressing of stone, concrete or slag. | 
