Easy Half Lap Joints

If you’ve ever tried to cut a half lap joint and been frustrated with the results, welcome to the club. Up until now my lap joints were pretty much hit and miss. Sometimes perfectly flush, other times loose or cut too deep. I grew tired of the inconsistency and decided there must be a better way!

After extensively looking into the methods others have used, I’ve come up with a fail proof method that will allow you to cut accurate and consistent half lap joints every single time. The best part: You don’t need a dado stack or any elaborate jigs.

Step 1: Tools

For this method, you’ll need the following tools:

• Table saw
• Crosscut Sled
• Combination Square
• Quick-grip clamp
• Spacer with the exact same thickness as your saw blade - I'll show you how to make your own spacer

Step 2: Make a Custom Spacer

The secret to this method is so simple yet extremely effective. The key is to make a custom spacer that is the exact same thickness as your table saw blade. Many blades are 1/8” so you could easily use some 1/8 plywood. For thin kerf blades, you’ll need to make a spacer to spec.

Find a small piece of wood, like a 1x2. Using your crosscut sled, start by squaring off the end, then slice off a tiny piece roughly 1/8” thick.

Remove the crosscut sled, and raise your saw blade. Place a piece of scrap birch plywood on each side of the blade (like a saw blade sandwich). Try to fit the spacer into the sandwich (spoiler: it likely won’t fit). Lay some sandpaper on a flat surface and sand the faces down until the spacer fits between the plywood boards.

Make sure you mark this spacer KEEP! so you don’t accidentally throw it out.

Step 3: Find Half the Thickness

The first step to cutting a half lap joint is finding the exact mid-point between the top and bottom of your board.

While you can certainly measure the thickness and divide by half, this can sometimes be impractical and lead to slight error. An easier method is using a combination square. Set it to roughly half the thickness of the board. Trace a line from the top and then switch to the bottom. Adjust the combination square until both lines are on top of each other. You’ve found dead center.

Step 4: Adjust Your Blade Height

With your crosscut sled in place, slowly raise the blade until it creeps up close to the line, but still beneath it. It’s better to progressively adjust upwards, rather than to cut too deep on the first pass.

Using a scrap piece of wood with the same dimensions as your workpiece. Shave off one end, then flip the piece over and repeat. You should be left with a thin shaving between the two cuts. Gently raise the blade and repeat the cuts. Adjust progressively as needed until the shaving is fully sliced off.

Step 5: How to Cut Corner Half Lap Joints

To cut half lap joints at the end of 2 boards, let’s say to make a frame, follow this method:

1. Lay one of the workpieces (A) up against the saw blade
2. Butt a stop block up to this piece and clamp it down to the crosscut sled
3. Remove workpiece A
4. Place your spacer up against the stop block
5. Butt the other workpiece (B) up against the spacer
6. Make the cut
7. Remove the spacer
8. Make repeated cuts between the initial cut up until the end of the workpiece
9. Repeat the steps for the second workpiece (A)

Step 6: How to Cut Midway Half Lap Joints

You can also use this method to cut half lap joints anywhere along the workpiece, whether it be in the center or 1 inch from the end. Simply mark where you want the joint to be and use that as a reference line for your first cut. Then follow these steps.

Tip: watch the video to see it step-by-step.

1. Position your workpiece (A) on the crosscut sled and line up the mark you made with the right side of the sled’s kerf line
2. Butt the second workpiece (B) (or a small scrap with the same exact dimensions) perpendicularly up against the workpiece, to the right
3. Butt a stop block up to this piece, again to the right, and clamp it down to the crosscut sled
4. Make the first cut.
5. Remove workpiece B
6. Place your spacer up against the stop block
7. Butt your workpiece (A) up against the spacer
8. Make the cut
9. Remove the spacer
10. Make repeated cuts between the 2 cuts you made above
11. Repeat the steps for the second workpiece (B)

Step 7: Final Adjustments

After making the cuts, you may find that the fit isn’t 100% perfect. Simply use some sandpaper to even out the bottom of the joint and remove the bumps caused by making multiple passes with the saw blade. Test again and you will find a perfect fit.

Be sure to check out the video tutorial if you haven't already done so. Please subscribe to my YouTube channel for more DIY video content.

You'll also find more projects on my website at diymontreal.com projects like:

• The Ultimate Lumber Storage Cart
• Homemade Corner Clamping Jig
• Twin Cutting Boards

Comments

[spry81]

How would I cut a half lap in a stick longer than my table saw? I want make a 6ft high leg with a half-lap cut and attach a horizontal 2" half-lap piece. The leg piece would stick out past my sled.

[erik.nottleson]

Thank you for such a clear and simple technique in your video. You as a woman also help me to reinforce for my girls that wood shop is for all.

[diymontreal]

Absolutely!!!! That make me really happy to hear :)

[oceandubman]

Making a kerf spacer using your method is sheer brilliance. I so happens that I have been working all week on making half laps and cross laps and have been only marginally successful. I am looking forward to returning to the shop tomorrow to make them using your techniques. Bravo!

[diymontreal]

Awesome! I'm so glad to hear my tips will be helpful to you exactly when you need them!

[barthalomew]

Genius.

[Azze01]

There's an even easier way to cut the joint without having to cut and use the kerf spacer:

1. Clamp a stop block to the crosscut sled fence so it touches the left side of the saw blade.
2. pull back the sled to get the blade out of the way
3. butt up the workpiece (perpedicular to the fence) against the stop block from the right hand side
4. butt up another stop block against the workpiece, again from the right hand side. Clamp it against the sled fence.
5. remove the left stop block, turn the workpiece, align it along the fence and butt it up against the right stop block
6. make the first cut.
7. Make repeated cuts to finish the halflap joint

[steadfast4life]

I wish I would have seen this years ago. Nice job!

[11557]

Use the pieces your want to join as templates to mark each other, then cut inside the lines with a handsaw almost to the halfway point. Make several cuts so that the remaining stock is easy to chip out with a chisel. Then either chisel or sand the bottom of each part until the joints are flush. When sanding a joint like this, use a hard block with sandpaper wrapped around it, and sand both parts at once to keep them the same.
You could also do the same joint with a router, gradually increasing the depth until the joint fits flush.

[11557]

Thanks for the pointers! Your method is good, but I find it simpler (no square, no pencil) to trim two pieces and test fit them. I shave both pieces just like your first cut, repeating until they fit flush.

[Tjfh]

Great. Finally a simple and accurate method. Sneaking up on the centre is very cool--that's usually where I have problems. Using the kerf spacer is similar in concept to several "kerf makers".
Thanks.

[diymontreal]

Thanks! And yep, came across the concept of a "kerf jig" which also seems like a similarly effective method.

[Drewno52]

Using a spacer equal to saw kerf, genius! Thanks for sharing your work in developing this method.

[diymontreal]

Thanks! I've seen a lot of different methods, some with store bought spacers, but they never worked for me. They did however spark the idea of making a custom spacer. :)

[CraftAndu]

Great tip! Thank you so much for sharing! :)

[diymontreal]

Thanks, my pleasure!

[fschill1]

Just spit balling. I've limited success using my stacked dado. probably the blades moving around under pressure. I love your system, but was thinking that if you made all the initial cuts, you could then use the table saw with a home made tenoning jig and raise the blade to the height of the lap and cut all the pieces.
I think except for other than end laps this might be easier than chipping away the material.

[diymontreal]

I totally understand where you're coming from, but since my previous techniques didn't really work for me, I'm not really in the best position to give you any recommendations!Have you tried making them by hand using a sharp chisel? I think with practice you can get pretty good at this. Otherwise I have seen people make them with a miter saw but not sure how accurate that would be. You could look into that. Good luck!