How Thick Should a Tenon Be

Tenons are a way to join two pieces of wood together – so you may come to wonder, how thick should a tenon be exactly? In this article, we will discuss everything you need to know about tenon thickness in detail. 

The tenon thickness should be 1/3 times the entire thickness of the tenoned workpiece and 1⁄2 –2⁄3 the length of the mortised workpiece. Tenon width should not exceed 5 times its thickness, with 4′′ being the maximum before using more than one tenon. The mortise depth for a blind mortise should be 2/3 the width of the board being mortised.

The general rule is that the minimum length of the tenon is five times its thickness. If you look at old furniture, you’ll notice that this “rule” has been broken, or perhaps the furniture was constructed before the rule was established. Keep on reading to know about the new ways to cut perfect tenons.

Step-By-Step Guide to Cut Perfect Tenons:

Here’s a quick video to size mortises and tenons in the right way!

Step 1: Start by cutting the tenon cheeks

Cut the tenon cheeks first. Set the blade height and determine the tenon thickness with a test piece. You’ll need a mortised workpiece nearby to double-check the fit. At this stage, your “stub” tenon should be a snug fit.

Step 2: Make a note of the tenon thickness

To evaluate the tenon length, you’ll need to change the location of the rip fence. Make a pass with the barrier set to just shy of the shoulder line. Then move the fence until the cut is completely aligned with your line. Return to the beginning of the tenon and make several passes along the cheek to eliminate any residual waste.

Step 3: Knockdown the ridges

On the tenon cheek, the dado blade frequently leaves tiny ridges. To knock down the ridges, move the workpiece forward slightly between each pass. It’s conceivable to do the same thing with the opposite cheek.

Step 4: Take note of the mortise width

After cutting and smoothing all of the tenon cheeks, the bottom and top shoulders are cut to complete the tenons. To appropriately size the tenon’s width, you may need to change the blade height.

Step 5: The key to a clean shoulder

On the waste side of the scribe lines, make a series of shallow passes with a chisel to carve a groove about 1/16 in. deep. This helps establish the top of the shoulder and displays more of your deep scribe lines.

Step 6: Trim the cheeks if necessary

Test-fit each tenon, then use a rabbet block plane or shoulder plane to remove extra thickness until a friction fit is achieved. If the tenon is excessively wide, use a chisel to narrow the edge.

Step 7: Examine the shoulders

Trim the shoulders square and flush to the line left by the cutting gauge if necessary. With a shoulder plane, this should just take a few passes.

Step 8: Cut the top and bottom shoulders

Start at the tenon’s end and work your way back toward the shoulder to get rid of the waste. Then, if required, use a “sideways” pass to smooth the face. The tenon is ready to meet its mortise after cutting the top and bottom shoulders.

Pro tip! Layout mortises a hair broader than your smallest chisel’s width to make chiseling out waste easier later. 

Tenon Strengthening Techniques

Dan Bollock, a wood researcher, broke more than 150 mortise-and-tenon joints of various lengths, widths, and thicknesses to examine how fit, size and glue-up processes affect joint strength.

He discovered that width is the most critical factor, but thickness and length are also significant. Unsurprisingly, a well-fitting joint is more durable. Glue was also applied to both the tenon and the mortise to generate the strongest glue bond. He also discovered that the final joint fit and glue-up method impact the joint’s strength.

Majority of the testing was conducted to see how the tenon’s size influences its overall strength. Bigger was immediately related to a stronger joint in all three dimensions—length, width, and thickness. They selected 38-inch-thick tenons for the length and width testing, which is a pretty standard size. The widening of the tenon had the most significant impact on the joint’s strength. The strength increased by 140 percent as the width expanded from 1-1⁄4 in. to 2-1⁄4 in., and a 3-1⁄4-in.-wide tenon tested 291 percent stronger than a 1-1⁄4-in.-wide tenon.

The fit of the tenon in the mortise was another critical aspect of the joint’s strength. The testing revealed that tight-fighting joinery is required and that glue cannot be relied upon to repair even minor gaps. The gap surrounding the tenon should ideally be less than 0.005 in.

How to Determine the Width of the Tenon?

This one is a little trickier. In Ellis’s book, there are two rules. To begin, cut the tenon one-half the width of the rail you’ll be cutting it on (a 2′′-wide rail will yield a 1′′-wide tenon). Second, if the tenon’s width is greater than six times its thickness, it should be broken into two (or more tenons). For example, on a 6-inch-wide rail, you want to cut a 1/4-inch-thick tenon. According to Ellis’ guideline, your tenon should be 3 inches broad. A 3′′ wide tenon, on the other hand, is greater than a 1-1/2′′ wide tenon, which is six times the tenon thickness. As a result, you’ll need to split that tenon into two 1-1/2′′-wide tenons.

What Factors Go Into Deciding What Tenon and Mortise Joint to Use?

This can be a challenging decision for newcomers. Here are a few guidelines to follow until you gain some experience with the correct joint for the proper application:

1. Keep things realistic

Sometimes the most basic joint will suffice. There’s no point in overcomplicating things, and going overboard might be harmful. For example, not every mortise-and-tenon joint needs pinning; glue would be enough.

2. Stick to what has worked in the past

There’s a reason why things have been done specifically for decades in woodworking. Exaggerating a section of a joint can help woodworkers recreate a joint.

Examine well-known works to use as models. Copying what has worked in the past is the safest method to make successful furniture.

3. Check if it fits properly

If you go to the trouble of making it, make sure it fits correctly. When the glue breaks, sloppy joins will fall apart early. Take your time, inspect your work, and replace any loose or damaged parts.

4. Make sure your work is neat

Each piece you make should be the finest you have to offer at the time. You should not think when you look at your work, “I could have done it better.” Shortcuts and sloppy work will follow you around for the rest of your life.


How deep should Mortises be?

The mortise depth should be approximately three times the tenon thickness. It can be cut in a variety of ways, including the conventional method of chiseling out the hole by hand using powerful mortising chisels and a mallet.

Should tenons be pinned?

Mortise and tenon joinery was famous long before woodworkers had access to dependable glues. A wood pin was one of the most frequent methods for repairing a mortise and tenon joint. Although gluing a mortise and tenon together is now simple, a pinned joint can be just as strong and may even provide some benefits. The process of pinning a mortise and tenon joint is relatively simple. However, like with any woodworking process, a little know-how and a few pointers can make the job go more smoothly.

Final Thoughts:

A mortise and tenon joint is a basic but effective way to put two pieces of wood together. For thousands of years, woodworkers all across the world have used it to join pieces of wood, primarily when the adjoining parts meet at right angles. Hopefully, with the help of our article, you will be able to size your tenons accordingly and make sturdy constructions! 

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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