How should I lay out this half lap joint?

[Dan Mitchell]

Still working on this coffee table I've posted about a couple times. Got the top & legs done, now I'm working on the runners which connect the legs at opposite corners & which cross under the middle of the table "X" fashion. I'm planning to plow out the material where the 2 runners "half lap" with a dado set in the TS, but how can I accurately lay out the weird angle on the 2 boards where they cross? Any hints on the DADO part would be appreciated too. I have an Osborne miter gauge I thought I'd use, set at the correct angle. I hope my description/question isn't too confusing.

I should add that the wood is walnut, and the runners are ~ 1.5"W x 2.25"H x 38"L.

TIA

Dan

[Tony Bilello]

Generally I always use my dado for half laps but in this case I would probably either hand cut the half lap or make a throw-away jig for a hand held router. Fitting, measuring and test cutting blindly would be too time consuming for the one joint in the center.
If you are talking about the leg to runner joint, then I would use the dado with a simple angle finder and stop block.
In either case, I would make full size test pieces to make sure all is right.

[Doug Shepard]

I think I would draw the pieces on the underside of the top then set a bevel gauge to the lines to pick up the angle. Then use that to set the Osborne. Then erase/sand off the pencil lines on the top when you're done.

[Peter Quinn]

I would make a gauge block to go between a stop on the miter gauge and the end of the stretcher. Basically you need to plow a trench 1.5" wide in each piece to let your opposing runner fit. Thats 2(3/4") which makes things convenient. You have one angle for both pieces, one height (roughly 1.125) that you can get to with test pieces, those parts are easy.

Set up a perfect 3/4" dado stack. For the half lap width I'd measure to the center of the stretcher and mark 3/4" off that mark in each direction at your desired angle, then make the first cut with the 3/4" gauge block installed between the work and stop. You have to set the stop so that with the gauge block installed the right side of the dado stack cuts the center line on your piece. Now remove the gauge block, and the LEFT side of the dado stack will be cutting the center line, leaving you a perfect 1.5" trench at your desired angle. Repeat with the other piece using all the same settings and its done.

It took more time to describe in keystrokes than it will take you to set up and process once visualized. If your stock is in fact exactly 1.5" than a piece of 3/4" MDF makes a good gauge block. The gauge block will allow you to add 3/4"+3/4" perfectly without having to hunt, peck, or work blindly. I would also attach a scrap sacrificial fence to the miter gauge to control tear out and clamp the work to the miter gauge for accuracy and safety. You may have too much dado blade in play at that height and angle to safely pass it without a secure connection between wood and miter jig.

Good luck and have fun..

[Jeff Bratt]

A sliding bevel gauge will be very handy for picking up the desired angle from your drawing, or by placing the full-sized pieces on the top itself. You can then use the gauge to set your miter fence. The attached drawing might help you visualize the layout - all the dark lines are the same length.
131495

The runners will need to be securely clamped to your miter fence, cutting at an angle like this has a tendency make the workpiece slip - especially when using a wide dado stack. I would have some sandpaper or other non-slip material on the face of the miter fence. I would sneak up to the layout lines for the width of the dado to get a snug fit for the lap joint. Of course, make sure you cut the top of one runner and the bottom of the other...

[Dan Mitchell]

Thanks for the replies. I made a couple pine test pieces & have determined the angle to be 34.7 degrees. Agreed about the clamping to the miter gauge. We'll see how it goes.

Dan