Woodworking Basics (The Taunton Press, 2003) takes a traditional approach to teaching, with the idea that learning basic skills is essential to craftsmanship. Author Peter Korn’s method helps new woodworkers learn the right techniques from the beginning; while more experienced woodworkers can use it to master classic furniture-making skills. This book provides a wealth of information including safe use of woodworking machinery, milling a board four-square and more. Two projects — a small bench and a side table — provide the opportunity to practice skills and develop confidence with tools. Learn how to cut a tenon, the piece that completes a mortise and tenon joint, in this excerpt taken from chapter 6, “Cutting a Mortise and Tenon.”
A tenon should fit a mortise snugly, like a hand in a glove. They should go together with noticeable friction, but not require pounding. An overly tight tenon can make assembly a nightmare and even split a mortise along the grain.
There is more than one right way to cut a tenon. The steps outlined below work well for me.
What You’ll Need
• Folding rule
• Mortise gauge
• 1-in. and 1/2-in. chisels
What You’ll Do
1. Measure tenon length and mark the shoulders.
2. Scribe the thickness with a mortise gauge.
3. Mark the width.
4. Pare back to the shoulders.
5. Saw the shoulders.
6. Saw the cheeks.
7. Re-mark and saw the width.
8. Clean up and fit.
Step 1: Measure Tenon Length and Mark the Shoulders
The mortise is 13/16 in. deep, and we’ve designed the tenon to be 3/4 in. long to ensure that it doesn’t hit bottom before the shoulders pull tight. With a sharp knife, mark the shoulder 3/4 in. from the end of the tenon piece, and square the mark around all four sides.
Accuracy is extremely important when marking shoulders. Hold the fence of the square firmly against the wood, and hold the knife blade at a constant angle throughout each cut. Position the knife for the second cut by registering its tip in the first cut, and so on. The last cut should meet the first cut perfectly. Register the knife tip in the first cut and slide the square into position against it to accurately mark the second shoulder.
Tool Tip: For greatest accuracy in squaring a line around a board, always register the fence of the square against a consistent edge and a consistent face. That way, if the edges and faces weren’t milled perfectly parallel, the line will still come out right.
Step 2: Scribe the Tenon Thickness
The mortise gauge should still have the same setting that was used for the mortise. Clamp the wood upright in a vise so both of your hands are free. Place the fence of the gauge firmly against the face of the wood. Scribe the tenon thickness around the edges and end of the board, from shoulder to shoulder.
Step 3: Mark the Width
The width of a blind tenon does not need to be cut as perfectly as its thickness. The significant glue bond will be formed between the cheeks of the tenon and the cheeks of the mortise, where long grain meets long grain. The width serves primarily to register the tenon in place.
Tenon width can be marked with a marking gauge or a pencil and square. To use the latter, which is my preference, measure in 1/2 in. from each side and square the width around the cheeks and end of the tenon.
Step 4: Pare Back to the Shoulders
Now that the tenon is completely marked out, the next step is to pare back to the shoulders with your 1-in. chisel. We do this for the same reason we pared back to the ends of the mortise, which is to give the chisel a clean start on the final finish cut.
Lay the wood flat on the workbench. Place a bench dog or stop at the far end to keep the wood from sliding away from you. On all four sides, pare a small groove back to the knifed shoulder line from the tenon side. Pare with the bevel down for greater control. Keep both hands behind the blade for safety.
Step: 5 Saw the Shoulders
Hold the wood in a vise or clamp it over the edge of your benchtop. Start sawing on a diagonal at the corner nearest you. Begin by guiding the saw against your thumb and starting with a couple of pull strokes. The saw teeth should be as close to the knife line as you can comfortably saw without actually impinging upon it. I usually leave about 1/32 in. Watch the saw cut down and across at the same time. Working in two dimensions keeps the saw straight in both.
Saw all the way across the board and down to the nearest scribe mark, which denotes the location of the edge of the tenon. Don’t saw the side of the board you can’t see.
Rotate the board 90° toward you and saw on the diagonal once again. This time, there will be a kerf as a vertical guide. Stop sawing when you have cut all the way across on the horizontal and down to the nearest scribe line. Rotate the board and repeat the diagonal sawing process two more times.
Finally, cut each shoulder down to the level of the tenon with the saw held horizontally. The existing kerfs will guide the saw.
Step 6: Saw the Cheeks
Place the wood in a vise on an upright diagonal leaning away from you. Saw on the waste sides of the tenon up to but not through the scribe marks left by the mortise gauge. The goal is to have the tenon fit right off the saw, with minimal paring. You can saw this boldly because the cheeks will be hidden: Accidental oversawing won’t create a cosmetic problem. Saw down and across simultaneously for greater control. Stop when you have cut across the end and down to the shoulder. Don’t saw on the side you can’t see.
Turn the board around and place it upright in the vise. Cut down the second side with the saw straight across. The existing kerf will guide the saw, if you let it. When you reach the shoulder, the waste piece should fall off the cheek. If not, the shoulder wasn’t sawn deep enough in the previous step.
Step 7: Re-mark and Saw the Width
When the cheek waste falls off, the width marks go with it. Re-mark the width, then saw to the lines.
Step 8: Clean Up and Fit
Once a tenon is sawn, a certain amount of cleanup is necessary. Start with the shoulders. Hold the work flat on the bench with dogs or a clamp. Use your 1-in. chisel to chop back to the shoulders in small increments of about 1/16 in. Then turn the work on the edge and use your 1/2-in. chisel on the narrow-end shoulders the same way. When you’re done, a straightedge should rest across the shoulders at any location without rocking. Slight back-cutting is permissible, so long as it is confined to interior sections of the shoulder, which will be invisible after assembly.
Next, try to fit the tenon into the mortise. If it is too thick or too wide, pare it down methodically to maintain squareness. Again, remember to clamp the wood or hold it in a vise while paring. Keep the back of the chisel flat against the wood to tell you where the high spots are. Pare with or across the grain, where possible, rather than against it.
The assembled joint should have a firm fit with snug shoulders. If the shoulders are not snug, either the tenon is too long or the shoulders are not flat. If the shoulders are snug on one side only, they may not be square across, or the mortise or the tenon may be crooked and require further paring.
If you feel there is room for improvement, begin again. Cut off the tenon to make the end square. Mark a mortise in a new location. Sharpen your chisels. Work carefully. Each step builds on the accuracy of previous ones.
With a reasonable commitment to practice, you will master the skill of cutting a mortise and tenon with hand tools. Once you can do that, you can do anything!
Tool Tip: An alternative way to flatten the shoulders is to use a shoulder plane, referencing the body of the plane against the cheeks of the tenon to keep the shoulders square.
Read more: The other half of this mortise and tenon project involves cutting a mortise. Learn about what materials you need and how to do it in How to Cut a Mortise.
“How to Cut a Tenon” has been reprinted with permission from Woodworking Basics: Mastering the Essentials of Craftsmanship by Peter Korn and published by The Taunton Press, 2003.