Video: How To Cut Half Lap Joints With A Table Saw
Half-lap joints are a great way to join two pieces together. There are several ways to cut a half-lap. In this video we show you how to cut a half-lap joint using a table saw and dado set.
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Video: How To Cut Half Lap Joints With A Table Saw - Video Transcript
Chris Marshal: When you need to connect to workpieces together that cross one another, like these frame joints, and you want to keep their faces flush, a good joint for the job is a half-lap joint. Half-flaps get their name because half the thickness of each of the workpieces is cut away, so they fit together to form one flat face. They're interlocking, and there's lots of surface area for glue, so they're really strong. Now, there are a lot of different half-lap joint styles, but in this video I'm going to show you how to make this one.
The workpieces have the same proportions, and the parts cross at some distance in from their ends. Now, to make this joint all you need is a table saw and a dado blade. I'm going to start by marking the layout line on each workpiece that establishes where the parts will cross one another, and then you can use the workpieces themselves as spacers to mark how wide the half-flap cuts need to be. Now, I'm marking these maple scraps because these are going to serve as my test pieces for my final joint parts over here. The thickness and width of my test pieces matches my final joint parts. That way I can dial in my saws setups and cut these first before making my final cuts on these. It's always a good idea to work from test pieces first.
Now, transfer those first two layout lines on each test piece up and around to the sides, they'll form the walls of the half-lap. Then connect them with a horizontal line that's centered on the part thickness, this is the bottom of the cut. Then, go ahead and layout the final workpieces the same way. Now, stack a wide dado blade in your table saw, it'll make cutting away the waste that much faster. Then raise the blade so the tips of the teeth just reach the bottom layout lines you've drawn on your parts. To cut these joints, I'm going to back up my workpieces with my miter gauge, it's got a long fence installed on it to provide plenty of support.
I'm also clamping a step off block to the rip fence, it's an index to line up the ends of the workpieces during cutting. I'm clamping it far enough in front of the blade, so my workpieces and the step off block won't be touching when I make each cut. Now, to setup this first cut, line up the edge of your dado blade with the inside edge of your layout lines, then pull the workpiece back and slide the rip fence over, so the step off block just touches the end of the workpiece, and lock down the fence. Go ahead and make the first cut, and be sure to keep the workpiece from shifting left or right when it leads to step off block. Make this cut on both test pieces and the actual parts.
Now, I'm ready to cut the other wall of my lap joint cut, and you set this cut up the same as the last one. Only this time, line up your cut with the other side of the dado blade, pull everything back, slide the rip fence over so the step off block just touches the end of the workpiece, and lock down the fence same as before. Now, make these second cuts to define the other wall of the half-lap. Then, shift the work piece over and cut away the rest of the waste in between. Do this only on the two test pieces. Now, try to fit your test joint together, and what you're aiming for here is a snug fit because these joints only get stronger when the parts don't fit together loosely.
Now, my test joint is just a little bit loose, so the way I'm going to remedy that problem is to shift my fence slightly closer to the blade on that second cut to cut a narrower opening, and if these parts hadn't fit together at all, I would have had to shift my fence a little bit further away from the blade to cut a wider opening. This is also a good time to check to see if your joint parts are meeting flush with one another, and you'll have to raise or lower the blade to adjust that fit. Now, if you need to make any adjustments, make a complete second round of tests cuts on the other end of your test pieces before committing to your final workpieces, to dialing your setup.
Once the test cuts are tuned up, finish cutting your final workpieces and you'll know that they'll fit together just like you want them to. So, whether your half-laps cross one another, like they do on this frame, come together on their ends like a picture frame, form a T-style joint, or even meet in X, now you know the basic process for cutting any half-lap joint. Thanks for watching.