Drilling operations; parts and assemblies

To make holes, slots and recesses in blanks, drill bits, pointed cutters and countersinks are used. The bit size must match the hole diameter, and the bit type is chosen by the drilling conditions and the shape and depth of the hole bottom. Holes across the grain that are shallow and blind are made with cutter-type bits. Holes whose axis runs along the grain are drilled with a spoon bit. For deep holes, twist, screw-type and auger bits are suitable: they drill both along and across the grain. Twist bits are durable. For blanks of chipboard, carbide-tipped tools are used. Order: a backing board goes under the wood, the blank is clamped in a machine vice, the centre is marked, the bit is fixed in the chuck, the teacher switches on the machine and the bit is lowered evenly. In a deep hole the bit is lifted from time to time to clear shavings. Shavings are brushed away after the machine stops, goggles are worn, and the blank is never held by hand while drilling.