Types of Power Drill Bits
Twist bits: sold singly or in sets of graded sizes for general use with power tools. Although designed for metalwork, they are more often used for drilling timber. `Green’tend to clog these drills — retract them frequently and clean out the waste compacted in the grooves with a nail or awl.
Auger bits: strictly woodworking tools. Centre spurs allow precise centring so that these bits will drill accurately in any grain direction.
Dowel bits: for flat-bottomed holes, using power tool at full speed. They are not as accurate as auger bits, especially when drilling into end grain
Countersinking bits: for ‘belling out’ the mouths of already drilledholes, allowing countersunk heads to be sunk flush with or slightly below the timber surface. Various sizes available.
Drill-countersinkers: combination bits which first drill a screw hole to the depth and diameter required and then bell out the mouth for the screw head.
Power bore bits: specially made for drilling larger diameter holes in timber, using. Power tools at full speed. One of the most accurate drills available.
Shell and parrot-nosed augers: long bits for drilling holes in standard lamp poles etc. on a lathe. They can be used freehand if a pilot hole is drilled first. When doing this, never drill more than 50 mm (2 in) at a time without retracting the bit and cleaning out the waste.
Slotting and shaping bits: patent tools with rasp-type shanks, used for elongating or widening holes previously made with a normal bit.
Hole saws: combination of centre pilot bit and ring-shaped saw for cutting large diameter holes through timber,and up to 6.5 mm (1/4 in) thick. Normally supplied with ring-saws of different diameters. Efficiency can be improved by filing down every other tooth. Masonry bits: twist bits with special alloy tips for drilling through brick, concrete, tiles, etc.
Spear point bits: for drilling through glass and mirrors. Use at low speeds and keep the work lubricated with turps substitute; keep a pool of it in a putty ring around the hole.
Flat bits: for general-purpose, large-hole boring.
After use, rub down bits with steel wool and wipe with a thin oil. Waste wood compacted into the grooves will cause bits to clog, overheat, lose their temper and so become useless.