How to Install Threaded Inserts in Plywood Without Splitting
Threaded inserts are a great way to create strong, reusable connections in woodworking projects. They're especially useful for router tables, shop-made jigs, knock-down assemblies, and accessories that need to be removed or adjusted.
But installing threaded inserts into the edge of plywood presents a couple of challenges. First, you need to drill a straight hole into a relatively narrow surface. Then, as the insert threads into the plywood, it can force the layers apart and cause splitting.
Fortunately, a few simple shop-made aids make the process much easier. In the video below, we'll show you how to drill accurate holes, keep threaded inserts aligned, and prevent plywood from splitting during installation.
Why Installing Threaded Inserts in Plywood Can Be Tricky
Threaded inserts are designed to provide durable metal threads in wood. Unlike driving a screw directly into the material, an insert allows a machine bolt to be installed and removed repeatedly without wearing out the surrounding wood.
However, plywood edges require extra care.
The alternating layers of veneer can separate when the insert's external threads exert pressure against the sides of the hole. And because plywood edges are relatively narrow, drilling at even a slight angle can cause alignment problems.
The key to a successful installation is keeping everything straight while supporting the plywood around the hole.
Make a Simple Drill Guide for Straight Holes
One of the biggest challenges is drilling a hole square to the edge of a long plywood panel.
A drill press makes accurate holes easy, but long or awkwardly shaped workpieces can be difficult to position on the drill press table.
A simple shop-made drilling guide solves this problem.
Build the Drill Guide
Start with a small scrap of plywood. Drill a hole through it using a drill press, making sure the hole is perpendicular to the face.
Next, attach a piece of 1/4" hardboard to the plywood block to create a fence. Quick-setting glue and a few pin nails make assembly easy.
The hardboard fence provides a reference surface that registers against the face of the workpiece, while the hole in the plywood block guides the drill bit straight into the edge.
One tip when attaching the hardboard: Keep the pin nails away from the guide hole. A nail driven into the drilling path can damage the bit later.
Position the Guide and Drill to Depth
Mark the center of the hole on the plywood edge.
Extend the centerline onto the drilling guide so you can align the guide hole with your layout mark.
Clamp the guide securely to the workpiece, using the hardboard fence to keep it properly positioned.
Before drilling, wrap a small piece of masking tape around the drill bit to indicate the required hole depth.
Then drill through the guide and into the plywood edge.
This simple setup allows you to drill accurate holes at the workbench without struggling to support a long panel on the drill press.
Chamfer the Hole Before Installing the Insert
Once the hole is drilled, use a countersink bit to add a small chamfer around the opening.
This serves two purposes.
First, the chamfer helps guide the threaded insert into the hole so it starts straight.
Second, it reduces the tendency of the plywood's surface fibers to lift or tear as the insert begins cutting into the material.
You only need a slight chamfer to make a difference. Avoid removing more material than necessary.
Use a Bolt and Nuts to Install the Threaded Insert
You don't need a dedicated installation tool to drive threaded inserts into plywood.
A hex-head bolt and a couple of nuts provide a simple way to turn the insert with a wrench.
Thread the nuts onto the bolt, then thread the bolt into the insert. Tighten the nuts against one another to lock them in position.
This arrangement makes it easier to drive the insert and remove the bolt afterward.
Lubricate the Threads With Paraffin Wax
Before installing the insert, rub a little paraffin wax onto its external threads.
The wax reduces friction as the insert cuts into the plywood, making it easier to turn and reducing the force required during installation.
It's a quick step that can make a noticeable difference, particularly when working with dense plywood.
Prevent Plywood Splitting With a Handscrew Clamp
The most important trick when installing threaded inserts into plywood edges is supporting the surrounding material.
As the insert threads into the hole, it acts like a wedge, pushing outward against the plywood layers.
Without support, this pressure can cause the veneers to separate.
A wooden handscrew clamp provides a simple solution.
Support the Plywood Around the Hole
Position the handscrew clamp over the edge of the plywood, with its jaws pressing against the two faces of the panel near the drilled hole.
Tighten the handscrew enough to support the plywood layers without crushing the material.
With the plywood supported, position the threaded insert over the chamfered hole.
Use a socket wrench to turn the installation bolt, keeping the insert aligned as it begins threading into the plywood.
Continue turning until the insert is seated flush with the edge.
Then back out the installation bolt, leaving the threaded insert in place.
The handscrew helps prevent the layers from spreading apart during installation, resulting in a cleaner, more reliable connection.
Tips for Installing Threaded Inserts Successfully
A few simple details can make threaded insert installation more consistent.
- Drill the correct hole size. Follow the manufacturer's recommended pilot-hole diameter for the insert you're using.
- Keep the hole square. A shop-made drill guide helps prevent crooked inserts, especially in long workpieces.
- Control the drilling depth. A tape flag on the drill bit provides an easy visual reference.
- Chamfer the opening. A small countersink helps the insert start cleanly and reduces raised fibers.
- Lubricate the threads. Paraffin wax helps the insert turn more smoothly.
- Support the plywood. A handscrew clamp helps prevent the layers from separating.
- Avoid overtightening. Stop once the insert is properly seated to prevent damaging the surrounding material.
For best results, test the technique on a scrap of the same plywood before installing inserts in your finished project.
A Simple Solution for Strong Threaded Connections
Installing threaded inserts into plywood edges doesn't have to be difficult. With a shop-made drill guide, a small chamfer, a little paraffin wax, and a handscrew clamp, you can make the process more accurate and reliable.
These techniques are especially useful for router tables, shop accessories, and woodworking jigs that use removable bolts or adjustable components.
The next time you need to install threaded inserts in plywood, take a few minutes to prepare the hole and support the material. Those small steps can help prevent splitting and produce a cleaner finished result.
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