Drilling Wood and Other Materials

Welcome to our guide to drilling holes in wood, metal and other materials that you will commonly encounter during DIY jobs. We will assume that you are using a power drill and that you have a range of drill bits for use with wood and metal.

The Right Drill Bit for the Right Hole

Starting with wood, for holes up to around ten mm wide a normal twist drill or dowel bit (like a twist drill but with a more open spiral) will do the job. For holes around eight mm upwards a flat wood bit (also known as a spade bit) will do better. This, as the names suggest, is flattened, a bit like a large screwdriver blade, but with a sharp tip and edges.

Larger holes still, for example to allow kitchen appliance drainage pipes to go through the sides of kitchen cabinets, will need hole saws. They are ordinary saws wrapped in a ring and mounted on a drill bit and are available in a variety of sizes.

Drilling the Hole

After measuring and marking where your hole should go, select the right size drill and position it over your mark. Start with a slow speed initially then speed up as the hole becomes large enough for the drill to get proper purchase. Don’t push too hard, let the drill do the cutting work and guide the drill, making sure that it is properly upright and at the correct angle to the wood.

Occasionally pull the drill bit out of the hole then re-insert it. This will allow waste material to come out and give the drill bit and wood a chance to cool down a little. Larger holes will need slower drill speeds to avoid overheating.

Flat Bits and Hole Saws

If you are using a hole saw or a flat (or spade) bit then always stop before you break through completely. Turn the wood over and complete the job by drilling from the other side, this prevents damage to the surface of the wood.

This needs accurate marking in the first place or you can drill a pilot hole right through the wood initially with a small diameter twist drill. This will act as a guide for the drill on both sides.

Metal and Plastic

With metal, and other materials like plastic, hard tipped twist drills will normally do the job. Do not drill holes in metal at too high a speed, if you have speed markings on the drill, generally 3000 rpm is the highest you should go. Higher speeds will not speed up the job but can damage the hardened tip of a metal drill bits

Metal is harder to drill than wood and will overheat more readily, so it’s often necessary to drill a succession of holes, gradually increasing in size, rather that going for one large hole straight away. Generally, the larger the hole diameter, the lower the speed you should use.

As a general rule of thumb you should not use a twist drill bit on metal that is thinner than the radius of the drill bit itself, as it will dig into the edge of the hole and damage the piece and possibly you as well. Instead, drill a small hole and then use a saw to enlarge the hole, or clamp up the sheet of metal with scrap pieces of wood either side and drill through the whole sandwich in one go.

Lubrication to Protect Drill Bits

With some metals you may find that lubricating the drill bit and the work area will speed up the job and make the drill bit last longer. For most of the metals that you will encounter while doing DIY – aluminium, brass, cast iron, steel and mild alloys – this isn’t strictly necessary but could be worthwhile, particularly if you are drilling many holes in one piece of metal.

Use white spirit, not oil, and replenish frequently. Plastics shouldn’t need lubrication and won’t respond to it very well.