Drilling screw holes

All screws must have pilot holes made before they can be driven home. For screws into softwood smaller than No. 6 gauge (3.5mm), make these with a bradawl. Drive into the wood with its chisel point across the grain, to avoid splitting.

Screws into hardwood and screws into softwood larger than No. 6 gauge need two pilot holes. One for the thread – the pilot hole – and one for the shank – the shank hole. These must be made with a drill and bit.

For all except the largest pilot holes, use twist drill bits. Those for pilot holes should be the same size as the screw core to which the threads are attached. Those for the shanks should match the screw shanks exactly. If you buy a set of twist drills, these will cover you for all screw sizes in common use.

When drilling pilot holes, mark the required depth on the drill bit with a piece of masking tape. This will tell you when to stop and cannot damage the workpiece should you overdrill.

As with nailing, where two pieces of wood are to be fixed together, screw the smaller to the larger. Drill the shank hole right through the smaller piece so it is pulled down tight as the screw is driven home. If the shank hole goes only part of the way through you will find it very hard to pull the top piece of wood down tight and may risk breaking or damaging the screw. Brute force should never be used – it indicates that either the thread hole or the shank hole is too small.


Countersinking is normally the easiest way of recessing screw heads flush with, or below the surface of the wood. The recess is made with a countersink bit after the pilot has been drilled, to the same depth as the countersunk screw head. Take particular care if you are countersinking with a power drill or the recess may accidentally become too large.

For some screw sizes, special bits are available to drill the thread hole, shank hole and countersink recess in one operation. Care should be taken, however, as they break easily.

Drilling techniques

Using the correct drilling technique makes all the difference to the quality of the finished work. Whether your drill is power or hand operated, you should always hold it at right angles to the work surface so that the pilot hole is straight. If you find this difficult, rest a try square upright next to the bit and use it as a guide.

Always use a power drill with the cable over your shoulder,. where it cannot accidentally become damaged or interfere with the work.

With bit drills, operate the drill in bursts and lift it frequently to allow debris to escape. To give yourself as much control as possible, always hold the drill with both hands and never press too hard – you are bound to overdrill.

Keep the chuck key taped to the cable, so it is handy whenever you want to change bits.

Using a hand-operated wheel brace requires slightly more effort, but gives more control than a power drill. When drilling vertically, grip the handle with your thumb on top. Turn the wheel steadily to avoid knocking the drill out of line.

To drill horizontally, grip the handle with your thumb towards the wheel. Alternatively, where a side handle is fitted, grasp this in one hand while you turn the wheel steadily with the other.

Avoid applying excessive body pressure to the wheel brace at all times or you will snap the bits.

Driving screws

Always make sure that the tip of your screwdriver is in good condition and that it fits exactly into the slot in the screw head. A blade which is too narrow or rounded damages the slot, while too wide a blade damages the wood as the screw goes in.

As a time-saving alternative to the conventional screwdriver, a pump-action screwdriver works by converting downward movement of the sliding handle into rotation of the tip. So, simply by pushing hard, the screw is driven very quickly in or out of the wood (depending on the setting of the ratchet).

When using a pump-action screwdriver, hold it firmly in both hands – one on the handle, the other on the knurled collar just above the bit – and make sure that you are not off-balance. A sudden loss of control causes the blade to slip out of its screw slot – damaging your wood in the process.

To make screwdriving easier, the screws can be lubricated with wax or candle grease before driving. Brass screws are quite soft and to prevent damage when screwing into hardwood, the resistance can be lowered by driving in a harder steel screw of the same size first.

Leave a reply