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Posted on November 23, 2007 in Carpentry
Many jobs around the house require a hole of some kind to be drilled - whether it is putting up a shelf, building a cabinet or hanging a light fitting. To drill a hole in any material, the correct type of drill bit must be used. It must be used correctly and be sharpened as appropriate.
A set of high-speed steel twist drills and some masonry bits can meet basic requirements. But for more sophisticated jobs, bits must be larger or designed for a specific material/purpose.
Good quality drill bits can be expensive. So take proper care of them. Keep them in a case or box if possible. Don’t allow them to roll around loose in a toolbox where the cutting edges may be damaged.
Learning how to sharpen drill bits is cost effective. It is better to keep a bit sharp by occasional sharpening rather than waiting until it becomes really blunt. A sharp bit cuts better with less effort whether used in a power or hand drill. A sharp bit will also give a cleaner hole.
Twist bits are most commonly used drill bits. They are usually referred to as twist drills. It can be used with either a hand or electric drill. The front edges cut the material and the spirals along the length remove the debris from the hole and tend to keep the bit straight.
Twist bits can be used on timber metal plastics and similar materials. Generally twist bits are made from either high -speed steel or from carbon steel.
Twist bits made from ‘high speed steel’ [HSS] are suitable for drilling most types of material. When drilling metal the high-speed steel stands up to the high temperatures. Twist bits made from ‘carbon steel’ are especially good for drilling wood. They should not be used for drilling metals. They are more brittle and less flexible than HSS bits.
They are also available coated with Titanium nitride (TiN). They can be easily identified by the golden color. This coating increases the hardness of the bit and adds a self-lubricating property. The coating is more effective when metal is being drilled. It has little effect when working with other materials.
Twist drills are usually available in sizes of 0.8-12 mm plus. They are useful only for drilling relatively small holes. They sometimes tend to clog quickly especially when the wood is green. So when drilling deep holes, especially in hardwood, the bits should be withdrawn regularly to remove the waste.
As these bits are thin and brittle special care is required when using the smallest sizes. Always better hold the drill square to the work and apply only light pressure when drilling. For sharpening use a drill sharpener, a grindstone jig or an oilstone. Titanium nitride bits cannot be sharpened without destroying the coating. Forming the correct angle at the tip is important for efficient cutting.
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