Ultimate Guide to Pre-Drilling Wood

Pre-drilling wood is something every woodworker should be accustomed to if they have experience. It is important because wood while being extremely strong can also be fragile. It is an extremely durable material that can last years, even centuries in some cases. However, if you don’t treat it right, and perform maintenance on it, it can deteriorate and break. If you force screws into the wood you can end up breaking it or cracking it. So it is necessary to pre-drill wood before you drive fasteners in it. So to help you out, we made the ultimate guide to pre-drilling wood.

To pre-drill wood, you need to start by marking where you need to drill. The drill bit should be the exact size of the body of the screw, excluding the threads. Then you need to place the drill perpendicular, or the angle you plan on driving the screws. You can use a drill stop to make sure you don’t drill too deep. Afterward, you start drilling but don’t force the drill in. Once you are finished, use the reverse drilling function to pull the bit out. Once that is done you just drive the screws in manually or use an impact driver.

While wood is a very durable object, driving metal fasteners in it can weaken it. This is because wood is composed of layers of fibres that give it strength. However, these same fibres are also its biggest weakness as you try to push the grain apart, it starts to split and crack. This is why every woodworker knows that you should avoid working against the grain. Always go with the direction of the grain so you don’t push it apart and crack it. 

How to Pre-Drill Wood: Step-by-Step Guide

Pre-drilling wood is a very simple technique that can help drive metal fasteners into the wood without splitting it. All you need is the right drill bit of the proper size.

Step 1 – Marking the Pre-Drilling Holes

Preparation is the key to avoiding mistakes in woodworking. The same goes for pre-drilling wood for your screws or nails. Marking the areas where you need to drill helps to keep the spacing equal. It also gives you a good idea of exactly where to start drilling. Using a pencil or a pen mark the areas where you need to pre-drill your wooden board.

Step 2 – Choosing the Right Drill Bit

Depending on the angle you need to pre-drill the wood, you need to choose a bit accordingly. Usually, for fasteners, you need to use a twist bit. However, if the screw is big enough you can use a brad-point bit. Though if you are drilling at an angle you can’t use a brad-point. For that, you can only use a twist bit, because brad-points are only good for perpendicular holes. Twist bits on the other hand have a tendency to walk, so use a very small-sized bit first. You can gradually increase the size of the bit to that of the size of your fastener.

Step 3 – Drilling

Place your drill at the right angle over the marked area where you are going to bore. If it’s perpendicular to the board, use the level on your drill or a perfectly squared object to keep your drill at 90 degrees. If you are using a brad-point then you won’t have to use a smaller bit as the sharp edge prevents the drill from walking. Though on the other hand if you are using a twist bit, use a smaller bit so that it does not walk and then a bigger bit so that your drill stays straight. Don’t push the drill in or force it, let the drill do its job. Once you are at the proper depth, you can use the reverse drill function to pull the drill out.

Step 4 – Cleaning

Using a blower clean the hole that you pre-drilled in the wood. Usually, the drill flutes pull out the chips of wood. However, if the bit size is small, the flutes can’t transport bigger chips. If you don’t clean the holes, your fasteners can’t be driven all the way in. They might also get stuck there due to having debris inside the hole. So clean it up using a vacuum or a blower.

Why Should You Pre-Drill Wood?

As we said before, while wood is a very durable material, it still requires care and maintenance. It will repay your care by outliving materials like brick and concrete. Pre-drilling wood is an essential step toward caring for wood. There are a few reasons why it is important, the most important being to prevent the wood from cracking and splitting. Wood is composed of layers of fibres that are tightly stuck together. When you push them apart by driving a nail or screw in wood, it cracks apart.

To prevent this from happening, you can pre-drill your wood. This helps the wood remain structurally strong. This way you are not splitting the fibres apart but cutting into them to carve a hole. So you can drive in metal fasteners without worries about cracking or splitting wood. If you don’t pre-drill wood there is a 50-50 chance that it might crack and split or they don’t. Why take the risk and waste perfectly good resources and materials like wood?

Also pre-drilling wood is not just for boring pilot holes. It can also be used for clearance holes which are different. While a pilot hole is big enough for the body of the screw, it is not large enough so that the threads pass through it. The threads bite into the wood allowing it to grip tighter. On the other hand, a clearance hole is bigger in size, so the threads don’t bite into the hole wall. It is bigger than the screw including the threads, but not big enough to let the shank pass.

What Size Holes Should You Pre-Drill

The size of a hole that you pre-drill is usually determined by what you are planning to do with it. For instance, if you are planning on driving a metal fastener into the wood, then you would go for a pilot hole. However, if you plan on joining two pieces of wood together, then you would go for a clearance hole. A clearance hole is slightly larger than a pilot hole on the top piece of wood, while the exact size of the body of the screw, excluding the threads, is on the bottom piece. So the size of the hole will depend on the type you are going for.

A pilot hole needs to be the exact size of the screw not including the threads. It is slightly smaller than the threads so that they can bite into the wood gripping them tightly. However, they are smaller than the shank of the screw. So you need to make the hole exactly the size of the screw you are using.

The size of the hole also depends on the wood you are using, if you are using softwood, then you should pre-drill the hole slightly smaller than the body of the screw. In softwood, the fibres and grain are not tightly packed together. This means driving a screw with a slightly smaller pilot hole does not crack it. Instead, it helps the threads of the screw to grip the wood tightly. However, in hardwood, you should go for the exact size of the body of the screw for a pilot hole.

How to Make Sure You Don’t Drill Too Deep

Drilling comes naturally once you are experienced at it. You don’t drill at the wrong angles or too deep. Drilling too deep can cause your fasteners to not grip the wood properly. There are plenty of ways in which you can make sure you don’t end up making too deep a hole. One of the most common ways is to use a drill stop. They are very reasonably priced and can be found easily online. There are many types of drill stops that you can attach to the drill bit. It stops the bit from going in too deep and it is easily adjustable according to the screw or nail size.

If you don’t have the time to wait for your drill stop to arrive, there are a few things you can do at home. You can use a piece of tape that will tell you where to stop drilling. Usually, you end up over-drilling when you are pushing too hard, so avoid doing that as well. If you use tape and don’t push the drill in forcefully then you will know where you have to stop. If you have more confidence in yourself you can also just mark the drill bit with a marker. This will help you know where you stop as well since you can see when the marked area on the bit reaches the very end of the board while drilling.

What Do You Use to Pre-drill Wood

To pre-drill wood, you will need a good drilling machine, a few drill bits, and a drill stop.

1. Drilling Machine

To pre-drill wood, you would obviously need a good drill. These days finding a drill set isn’t too difficult. There are many reputed brands that you can choose from to find the best drill set. However, not all drills are made equal, some perform better than others. A wired drill works extremely well, however, it reduces portability and mobility. A wireless drill on the other hand is as good as the power it gets from its battery. The more powerful the battery is, the more torque and speed the drill gets.

Usually, the more expensive an item is the better its quality, but you don’t have to spend big bucks to get a good drilling machine these days. The Ryobi 18V One+ Drill Set is impeccable and affordable. It uses a universal 18V battery that can be used in any other 18V tool from the Ryobi brand. Which can be a good investment if you are planning on buying more than just a drilling machine.

2. Drill Bits

Drill bits are just as important to pre-drill holes as a drill machine since both can’t actually do their job without each other. There are different types of drill bits available for making holes in wood. The basic ones are twist bits, brad-point bits, and spade bits. We also have Forstners and counter-sink bits for drilling wood too. They range more on the expensive side though, and besides, Forstners aren’t usually used for pre-drilling wood for pilot or clearance holes. Forstners are usually used for wood when you need to make large holes in it, and so are spade bits. 

Other than the type of bits, we also need to look at the quality of the bits as well. Having a basic no-name set of drill bits will only lead to uneven and at times holes that aren’t clean. To prevent that buying quality bits matters a lot. Quality bits also last for a long time, they retain their sharpness for a long as well. Twist bits double up for drilling metals too, so buying a good quality set is not a bad idea. For instance, this Milwaukee Titanium Twist Bit set of 20 bits is great for both wood and metal at the same time. Then we have these DeWalt Brad Point Drill Bit Set which is very cheap, so even if you break a few bits it won’t be an issue.

How to Pre-drill Wood for Lag Screws

Lag screws are great for decking and fencing, they are strong and can hold large-sized boards in place. They are specifically great for outdoor use because of this purpose. Lag screws also require pilot holes just like normal screws. Pre-drilling holes for lag screws are not any different. However, because the size of the lag screws is way bigger than normal ones, the pilot holes need to be precise. Here is a chart of what size pilot holes you need to pre-drill for lag screws.

Lag Screw DiameterPilot Hole Size for HardwoodPilot Hole Size for Softwood

As you can see, the size of the holes you need to pre-drill is different for both hardwoods and softwoods. Softwoods don’t have densely packed fibres while hardwoods do. The lower density of the wooden fibres in softwood helps with the compression of screws in a smaller hole. While you need to make sure that the size of the hole you pre-drill in hardwood is not too small as forcing it might crack it.

Pre-drilling Softwood vs. Hardwood

Softwood and hardwood are very different in how they act and not just in the way they grow. Hardwoods are usually denser than softwoods due to how they grow. So you treat both hardwoods and softwoods differently. They take differently to finishes, tools, and to screws as well. When you are pre-drilling holes for wood, make sure to know which species of wood you are working with.

Softwoods have low-density fibres, they aren’t so tightly packed and woven together compared to hardwoods. You should always pre-drill a smaller hole for them since you want the threads of the screws to bite into the fibres of the wood better. However, if you are pre-drilling for hardwood, you need to make the hole exactly the same size as the body of the screw. This is because hardwoods have dense fibres and they don’t get pushed easily. There is a high chance you might crack the wood if the hole you pre-drill is too small for the screw.

FAQs- Frequently Asked Questions

How deep should I pre-drill?

You should only pre-drill as deep as the body of the screw or nail you are making the pilot hole for.

Can you screw straight into wood?

No, you cannot screw straight into the wood, however, it is possible. There are huge chances of the wood cracking or splitting due to the pressure exerted by the screw. Since the screw is not cutting or carving the hole instead it is pushing itself into the wood, it can easily break the wood. So it is always better to make pilot holes before driving screws into wood.

Final Thoughts

Pre-drilling wood becomes easier with time and experience. Once you get to a certain level, you can eye the depth and the size of the hole. Until then it is no shame to use a depth stop and check out guides for charts and sizes. It is better to take help than to waste a perfectly good piece of wood by either drilling too deep or big. Either way, hopefully, this guide has covered everything there is to know about pre-drilling holes in wood.

Martin Swizz

Hi! This is Martin, I like to research, experiment, and learn new things related to wood carving and other kinds of woodworking.

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