Carriage bolts are used throughout the construction industry to join components together. Alongside their professional application, carriage bolts are also widely available for DIY and home enthusiasts.
Installation of the fixing is relatively straightforward, as long as the correct procedure is followed.
How to Install a Carriage Bolt in Wood
Read on below to find out how to install a carriage bolt.
Step 1: Gather the Materials and Tools You Will Need
Before you start, you will need to make sure you have prepared the following:
- Materials: Components, carriage bolt, nut, and a washer
- Tools: Drill, drill bits, spanner/ratchet, pencil, ruler, hammer, and a clamp (optional)
Step 2: Set Out and Mark Out Components
Here you want to understand where you will join the two components. If it is possible, clamp the pieces of together, in their final position.
Mark out a central point in the component with a pencil, this is where you will start to drill from. Ensure it is far enough from the edge that the entire head of the carriage bolt will sit on the surface.
Step 3: Drill
With the components firmly held in place, begin to drill through the first component. You want to make sure the drill bit is slightly larger than the diameter of the bolt. It should be a tight fit and you might have to hammer the bolt through. Also, the drill bit must be longer than the combined thickness of the two components.
Keep the drill steady as it passes through one component to the next. If any offset occurs, the components will have a step between them and not sit flush. Take your time and keep stopping to check if the drill is still perpendicular to the workpiece, this will help you to not drill at an angle.
Step 4: Insert Bolt and Tighten
Place the bolt through the clearance hole that you just drilled.
If it’s tight try tapping it in with a hammer. Once the bolt exits the second component place the washer over it and tighten the nut. Use the spanner or ratchet to tighten the nut, it wants to be firm but not overly strained.
Mistakes to Avoid
Here are some common mistakes you want to avoid:
1. Overtightening
Don’t overtighten the nut on the thread. This is for a few reasons. Firstly, if it is too tight, you will struggle to undo it if you ever need to. Secondly, you might damage, or even split the wood.
2. Don’t Forget the Washer
The washer spreads the force that pulls the two components together. This helps stop the nut from pulling into the clearance hole and damaging the component beneath.
3. Not Drilling Straight
If you drill at an angle, the flat surface of the head will not sit flush on the face of the timber. This has a couple of knock-on effects. Firstly, one side of the head will dig into the face and damage the component beneath. Secondly, there is potential that over time the joint will twist or warp.
4. No Access
Make sure that you have access to put the nut on the bolt and tighten it up. You need to be able to get your hand in there to put the nut on. You also need to have enough space to put either your spanner or ratchet over the nut.
Tips & Tricks
Next, here are some tips to make the job easier:
1. Clamp as Much as Possible
There are so many variables when you work with wood. The trick to working accurately is reducing the variables enough that you can control them. Struggling to hold the wood in place? Clamp it. This will free up a hand to drill straighter and let you concentrate on one task at a time.
2. Use the Right Drill Bit
To drill accurately, you need the right drill bit. You want to use a spurred wood bit for the most accuracy.
3. Wear PPE
You should always wear PPE when doing work like this.
Carriage Bolts: Frequently Asked Questions
Lastly, let’s take a look at some of the more commonly asked questions about installing carriage bolts.
Are There Differences Between Installing Carriage Bolts in Wood and Metal?
The materials are very different, so there will be differences yes
For example, when installing into wood, the components will likely be thicker than metal. This means the length of bolts you’d need to go through wood will be less.
Another point on this, wood has more tolerance than metal. This means that if you don’t get the size of the clearance hole right, you can’t ‘bully’ the bolt through metal.
Lastly, to drill through metal you will need a metal drill bit, not a wood one.
How Should You Choose the Right Size of Carriage Bolt?
To decide the right size of carriage bolt, measure the thickness of the two components that you will join. Then add the thickness of the two components together. On top of this measurement, you must add the thickness of the nut and the washer to the length of the bolt.
The thickness of the bolt should be determined by the weight it needs to hold. Ask for the technical specifications to see the limitations of each bolt.
Can You Hammer in Carriage Bolts?
No. You cannot hammer a carriage bolt in. You must drill a pilot hole first. The pilot hole will stop the wood from splitting. If the pilot hole is the right size, but a bit tight, you can hammer it in. But you cannot hammer the carriage bolt through the material without drilling first.
Do You Need to Use Washers with Carriage Bolts?
You should use a washer on a carriage bolt between the nut and the material.
How Do You Stop a Carriage Bolt from Spinning?
If you drill the clearance hole too big, the square section of the neck will not stop the bolt from spinning. To rectify this, there are three options to try:
- Try holding the rounded head of the bolt with a pair of thin nose pliers. Whilst holding the head, tighten the nut.
- Use two clamps to hold another piece of material tight against the head of the bolt. Then tighten up the nut.
- Use a hacksaw to cut a slot into the top of the head. Make it deep enough to get either a flat-headed screwdriver or a scraper into the cut. You can then use the screwdriver or scraper to hold the head from spinning while the nut is tightened.
For more details, read my detailed guide on how to tighten a bolt that keeps spinning.
Summary
Installing a carriage bolt shouldn’t be an intimidating task. If you follow the steps laid out in this article, you take your time, and you wear PPE – you will get the job done safely and successfully.
Make sure you have the correct equipment, that you can access the area safely, and that the bolts are the correct size. With all of this in check, your components will be jointed together easily and you can move on to the next task.
In case you are wondering, I also have an article on how to remove carriage bolts.