To drill a satisfactory hole in any material, the correct type of
drill bit must be used; it must be used correctly and be sharpened as appropriate.
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.
For basic requirements, a set of high-speed steel twist drills and
some masonry bits will probably be sufficient for the average handyman.
But for more sophisticated jobs/material, others bits will be required -
perhaps larger, or designed for a specific material/purpose.
Good quality drill bits can be expensive, so take care of them, keep
them in a case or box if possible, rather than allowing 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 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
Usuallyreferred
to as twist drills, twist bits are probably the most common drilling
tools used by the handyman 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.
They can be used on timber, metal, plastics and similar materials. Most twist bits are made from either:
- 'high speed steel' (HSS), these are suitable for drilling most types of material, when drilling metal the HSS stands up to the high temperatures.
- 'carbon steel', these bits are
specially ground for drilling wood and should not be used for drilling
metals, they tend to be more brittle, less flexible than HSS bits.
Twist bits are also available coated with Titanium nitride (TiN),
these are easily identified by the gold like colour. This coating
increases the hardness of the bit and adds a self-lubricating property.
The coating is only really effective when metal is being drilled, it has
little effect when working with other materials.
Twist drills are usually available in sizes 0.8-12 mm plus. They are
designed 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holes (especially in hardwood) the bits should be withdrawn regularly to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.
Special care is required when using the smallest sizes since these
bits are thin and brittle. Always hold the drill square to the work and
apply only light pressure when drilling.
Sharpening - use a drill sharpener, a grindstone jig or an oilstone.
Titanium nitride bits cannot be sharpened without destroying the
coating (although if the drill needs sharpening, the coating will
probably have already been destroyed). Forming the correct angle at the
tip is important for efficient cutting.
Screwdriver bit drills
Designed to fit in rechargeable screwdriver these bits have a
hexagonal shank. They are ideal for drilling pilot holes but are limited
by the low power of these type of screwdrivers and the limited size of
small bits available.
Sharpening - as for twist drills.
Masonry bit
As
the name suggests, these are designed for drilling into brick, block,
stone, quarry tiles or concrete. The cutting tip is often made from
tungsten carbide bonded to a spiralled steel shaft. Some masonry drills
are described as 'durium tipped', this term refers to a highly durable
silicon bronze alloy used instead of tungsten as the cutting point.
Masonry drills are usually used in a power drill; although they can
be used with a lot of effort in a hand brace. Most masonry bits can be
used with a hammer action power drill, but always check as the action is
quite punishing on the bit and cheaper bits have been known to shatter
when subjected to the pounding. Always use a slow rotational speed for
drilling into harder materials to avoid overheating the tip, and
frequently withdraw the bit to remove dust.
Long Masonry bits (300 to 400mm) are available for drilling through masonry walls.
Bit sizes range from 4 to 16mm.
Sharpening - use a drill sharpener or grindstone to sharpen the tungsten carbide tip.
Spur point bit
Also
known as a wood or dowel bit, they have a central point and two raised
spurs that help keep the bit drilling straight. The bit cuts timber very
fast when used in a power drill and leaves a clean sided hole. They are
ideal for drilling holes for dowels as the sides of the holes are clean
and parallel. Sizes range from 3 to 10mm. Spur point bits should only
be used for drilling wood or some plastics.
Sharpening - a bit fiddly as it has to be done by hand. Sharpen the
point and spurs with a fine file or edge of a fine grindstone; the angle
between the point and spurs should be 90°.
Bullet Pilot Point
With their central point and two spurs, Bullet drills resemble spur
point bits, but can be used in metal, wood and plastics. Unlike normal
twist drills, the twisted flutes are ground away; making a truer, more
accurate bit than normal twist bits. They cut a clean hole and cause
little damage when they break through the back of the workpiece.
Bit sizes range from 1.5 to 13 mm.
Sharpening - cannot be carried out satisfactorily.
Countersink
Although not a true 'drill', it is used in a power or hand drill to
form the conical recess for the heads of countersunk screws. These bits
tend to be designed for use on soft materials such as timber and
plastics, not metals. When used with a power drill to counter sink an
existing hole, the bit tends to 'chatter', leaving a rough surface.
Better results be will obtained if the countersink bit is used before
the hole is drilled, then take care to ensure that the hole is in the
centre of the countersunk depression.
Countersinks are available with fitted handles so that they can be
used by hand twisting, often easier than changing the bit in the drill
when only a relatively few holes need countersinking.
Sharpening: difficult, but can be done with a fine triangular file.
Countersink with clearance drill
These combination bits are quite clever, they drill the clearance
hole and countersinks it all in one stroke. Can be used in a power drill
or some routers. Different bits are required for different size of
clearance holes and they are probably not cost effective unless a large
number of a given hole size need to be drilled and countersunk.
Sharpening - difficult, due to shape of spur points.
Tile Bit
A
bit for drilling ceramic tiles and glass, it has a ground tungsten
carbide tip. They can be used with a hand drill, but are best used in a
variable speed power drill on a slow speed. When drilling glass, some
form of lubricant (i.e. turpentine or white spirit ) should be used to
keep the tip cool.
Ceramic tiles can also be drilled using a masonry bit if it is used at slow speed and without hammer action.
Sharpening - difficult because of the hard tungsten carbide and
curved cutting edge. With care and patience, a blunt edge can be made
good using an oilstone.
Flat wood bit
Intended
for power drill use only, the centre point locates the bit and the flat
steel on either side cuts away the timber. These bits are used to drill
fairly large holes and they give a flat bottomed hole (with a central
point) so are ideal where the head of a screw/bolt needs to be recessed
into the timber - always use this bit before drilling the clearance hole
for the bolt.
The larger bits require a fairly powerful drill to bore deep holes.
The bits cause a lot of splintering as they break out the back of the
workpiece - using a sacrificial backing board will reduce this. Flat
wood bits are not really suitable for enlarging an existing hole.
Sizes range between 8 and 32mm.
Sharpening - use a fine file, oilstone or grindstone.
Hole saw
Used
for cutting large, fixed, diameter holes in wood or plastic. They will
usually cut up to a depth of 18mm - deeper versions are available. Best
used in a power drill at low speed as the blade saws it's way through
the material.
Sharpening - could be done with a fine triangular file - as for an ordinary saw.
Combination hole saw
Like the Hole Saw above, these combination saws can cut large holes
but they consist of a number of different sized round saw blades,
usually ranging from about 25 to 62mm in diameter. Normally the blade
are secures by a radial screw in the 'head', all blades other than the
desired sized being removed before the screw is inserted to secure the
required diameter blade. Best used in a power drill at low speed as the
blade saws it's way through the material.
Sharpening - could be done with a fine triangular file and 'setter' as for an ordinary saw.
Forstner bit
Used
to form holes with a flat bottom, such as for kitchen cupboard hinges.
Best used in a power drill held in a drill stand as there's little in
the way of a central point. If used freehand, the positioning is
difficult to control as there is no central pilot bit.
Sharpening - on an oilstone or with a fine file.
Wood Auger bit
This
is ideal when drilling large-diameter, deep holes in wood or thick
man-made boards. Generally an Auger bit should only be used in a hand
brace. The bit will cut a clean and deep, flat bottomed holes. The
single spur cuts and defines the edge of the hole while the chisel-like
cutting edge removes the waste within the previously cut circle. The
threaded centre bites into the wood and pulls the bit into the timber.
This 'pulling' action means that the bit is really unsuitable for use in
a power drill.
Sharpening - use a fine file or oilstone to keep the spur and main cutting edges sharp.
