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Issue #277 - May 2003
Half Lap How-To Half Lap How-To
Strong and quick - two reasons why I use half-lap joints. They're strong because a half-lap joint provides a large face-to-face gluesurface (see Photo left). And they're quick because both workpieces can be cut using one setup.
To cut a half-lap joint, half the thickness of the stock is removed from each piece so the two overlap and their faces are flush. A table saw and a dado blade make quick work of this. Stock Thickness is Important - To ensure accurate results, all your stock needs to be exactly the same thickness. If it's not, you won't be able to cut the half laps so the mating pieces are flush on both faces.

Blade Height is also Key
- A second important factor is to set the dado blade to the proper height. It should be exactly half the thickness of the stock.

I start with a test piece and set the blade just under half the thickness of the stock. (Make sure the test piece matches the thickness of the workpieces.) Next, I make two passes, flipping the test piece over after the first pass. This leaves a thin sliver of wood, as shown in Fig. 1. Now to set the final blade height, raise the blade just a hair and repeat this pass-and-flip process until the sliver is removed (Fig. 1a).
Set a Stop - Once the blade height is set, the next step is to set up a stop to establish the shoulder of the half lap. I use my rip fence as a stop and set it so that the distance from the outside edge of the blade to the fence matches the width of the workpiece (Figs. 2 and 2a).
Cut & Clean Up - Now you're ready to cut the end laps (Fig. 3) and cross laps (Fig. 4). To do this, use an auxiliary fence on the miter gauge for the initial pass to establish one shoulder of the lap joint. Then remove the rest of the waste in additional passes.
Some dado blades will leave tiny ridges along the cheek of the half lap. To remove these ridges, slowly move the piece side to side over the blade.

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