Many woodworkers will say that when woodworking, you should always use a pilot hole before driving in a fastener.
But is that really the case?
At first glance, a screw hole appears to make sense only if you work with wood frequently or need to drive screws in.
But you will soon discover that there are several reasons to use a pilot hole and that it is a necessity when woodworking.
Pilot holes are necessary when there is even the slightest indication that the wood will crack, the screw may jam or break, or the wood is too hard to allow screwing.
It is also recommended to drill screw holes for the precise mounting of items.
The purpose of a pilot hole is to guide the drill bit and prevent damage when you drill the main hole.
Drilling screw holes can be very useful and affect the outcome of your woodworking projects.
But if you do not know when and how to use them, you may not get the right benefits from them.
In this article, you will learn in detail what pilot holes are, how to use them, and when to drill pilot holes.
- What is a Pilot hole?
- Why do you need pilot holes?
- What is the difference between a pilot hole and a clearance hole?
- When do you need to make pilot holes?
- How to make a Pilot hole?
- What are the most common pilot hole mistakes?
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What is a Pilot hole?
The term pilot hole refers to a slightly smaller hole that is drilled in wood, metal, or other material.
This hole will serve as a starting point in order to drill a larger hole or place screws in a later step of the (woodworking) process.
Often, a pilot hole is also be referred to as a screw hole or a predrilled hole.
Why do you need pilot holes?
Making pilot holes can be advantageous in woodworking for several reasons.
You will need pilot holes to prevent the wood from splitting, you can work more accurately, it can prevent screws from getting stuck or breaking off, and you can screw or drill with less effort.
The main reason to use screw holes is that they prevent the wood from splitting when you drive screws, which happens more often and faster than you think if you do not use pilot holes.
If you do not use screw holes before you put your screws in, you are more likely to end up with a damaged surface. This can be very annoying when you are working on a quality project or an expensive piece of wood.
Pre-drilled holes can also be drilled in preparation for the main hole, making drilling into wood or metal faster and easier. This will prevent the larger drill bit from dulling or burning quickly, and you will have to put in less effort. You can also pre-drill to prevent the drill bit from slipping when you start drilling into wood or any other material. This way you can work more accurately.
If you need to screw into hardwood, it may be a good idea to pre-drill as well, even if there is no risk of splintering the wood. The hardness of some types of wood can cause the screw to jam or, worse, break.
You’ll also need more power whether you are screwing by hand or with a cordless drill in hardwood when you haven’t pre-drilled first.
Why does wood split when screwing?
Wood consists out of fibers and cells that are filled with moisture as the tree grows. These cells are flexible and make the wood pliable.
Just think of how a tree can move during a heavy storm.
If these cells are not flexible, the tree will break with the slightest shake from the wind.
When we harvest wood for woodworking, it is first dried.
This causes almost all the moisture to disappear from these cells.
This makes the cells smaller and closer together so that the wood loses its flexibility.
When you turn a screw into the wood, it pushes the fibers and cells of the wood aside.
Since the fibers and cells are much less flexible and smaller as the wood dries, they are less able to take up the space the screw needs. Therefore, the impact of the screw will be distributed over a larger number of cells and a larger surface area.
If this surface area is too close to the edge of the wood, this can lead to splitting the wood.
What is the difference between a pilot hole and a clearance hole?
If you are new to woodworking, you may not know about pilot holes and clearance holes. Many people confuse pre-drilled holes with clearance holes, but there is actually a difference between the two.
The main difference is that when you drill a pilot hole, you drill it slightly smaller than the screw. This allows the thread to grip the wood.
With a clearance hole, you make the hole slightly larger, so the screw can pass through. This allows the screw to engage the material underneath and allows a perfect connection with the material above.
You can use a clearance hole if you are using fully threaded screws.
These are screws where the thread runs through the entire screw from the tip to the head of the screw.
With partially threaded screws, you do not need to make any clearance holes.
The only thing you need to make sure of is that the part of the screw that is not threaded matches the thickness of the material you want to fasten.
Otherwise, the thread will engage with the material above it and a perfect joint will not be made.
When do you need to make pilot holes?
I think it’s a good idea to pre-drill as much as possible.
As I mentioned earlier, there are many advantages to doing so, such as avoiding splitting the wood.
But most of all, I remember that it will save you a lot of energy.
Not only by having to use less force, but also by not having to solve problems like broken screws.
If you put thinner and smaller screws in the middle of softer wood like pine, you can safely screw without splitting the wood. The wood is soft enough to be pushed aside by the screw and drive it deep into the wood. I personally do this when using screws smaller than 5×50 mm and placing at least 5 cm from the edge.
However, there are a few reasons when it is highly recommended pre-drilling. I’ll summarize the most important ones here:
- When driving screws in Plywood
- When driving screws in MDF
- Drilling or screwing in hardwood
- Drilling, screwing or nailing close to the edge of the wood
- When using thick or long screws
- If you need to mount things very precise
- To locate the place when you need to screw from the back
- When you need to screw manually, so you can screw with less effort
Do I need to drill a pilot hole for self-tapping screws?
First, you need to know the difference between self-tapping screws and self-drilling screws.
Self-tapping screws, as the name implies, ensure that the screw pre-cuts the thread in the wood, making screwing smoother and faster.
In some cases, you can drive a self-tapping screw without a pre-drilled hole, such as when screwing into softwoods.
In most cases, however, a pilot hole must be made even when using self-tapping screws.
Self-drilling screws, on the other hand, can be driven into wood without pre-drilling, and better yet, some can even be screwed into metal without pre-drilling.
Below are two pictures of both a self-tapping screw and a self-drilling screw. Notice the differences at the tip of the screw.
Do I need a pilot hole for metal?
Unless you are using self-drilling screws, always drill a screw hole before driving a screw into metal.
Likewise, if you need to drill larger holes in metal, it is recommended to pre-drill with a smaller drill bit first.
I myself work with metal to a lesser extent. However, I’ve found that when I need to drill holes in metal larger than 5 mm, it’s much more convenient to pre-drill with a smaller drill bit first.
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How to make a Pilot hole?
Drilling a screw hole is simple and can be done in a few steps.
- Mark with a sharp pencil where you want the screw to go.
- Poke a small hole with an awl or a punch in case you want to drill or screw in metal.
- Choose the right pilot drill bit to drill the hole. I will go into more detail about this later in this article.
- Drill the pilot hole at the angle where the screw will be positioned and to a depth equal to the length of the screw.
What is a Pilot Hole Drill Bit?
A pilot hole drill bit is a term for the drill used to make a predrilled hole, after which a screw can be set or drilled further into the main hole.
A pilot drill can be a regular drill bit or a countersink drill bit that is slightly narrower than the diameter of the screw.
If you are using a regular drill bit, you can mark the depth with a depth stop for the drill bit, like the one you see on Amazon here.
Alternatively, you can mark the depth by putting a piece of painter’s tape on the drill bit.
With this drilling method, you can drill a hole without a countersunk hole.
However, if you want to pre-drill and countersink in one step, you can do so with a countersink drill bit like this one, which you can find on Amazon.
For a more in-depth article on the different types of drills and which ones you need for your workshop, check out this article — 7 essential types of drill bits — I wrote earlier. Also check out my article, What is a countersink bit? and how to use it properly)
If you want to know what size drill bit to use for a pre-drilled hole, you can use the body of the screw as a guide.
If you hold them up to the light one behind the other, the drill bit should be the same thickness as the body of the screw.
To make it even easier for you to determine the size of the drill bit for a pilot hole, I have created this chart of drill bit sizes for screw holes in inches and mm.
|Screw gauge #||Shank hole inches||Shank hole mm||Pilot hole softwood inches||Pilot hole softwood mm||Pilot hole Hardwood inches||Pilot hole Hardwood mm|
What are the most common pilot hole mistakes?
Although making screw holes seems like a simple task, you should still be careful not to make any mistakes. There are a few things you can do wrong that will not produce the desired result.
I am going to list some of the most common pilot hole mistakes.
- Drilling the hole too tight. This will damage the wood when you drive a screw into it.
- Drilling the hole too wide. The screw’s threads barely engage the wood, if at all, so the screw is not anchored enough and can come loose.
- The hole was not drilled deep enough. If you drive the tip of the screw into wood that has not been predrilled, the wood will split.
- The hole was drilled diagonally. This causes the screw head to protrude beyond the wood surface on one side. The end result is not clean and things can get caught on the screw head, causing damage.
- The drill depth stop is not set correctly. As a result, the screw is not fully countersunk or is too deep in the wood.
I hope you enjoyed my article on understanding what pilot holes are, and that you are convinced that making screw holes is just one of the many things you need to know before you start your next DIY project.
I think it’s clear now that they can make a big difference and affect the end result of your project.
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