Open ended mortise on the table saw

This little project started with a desire to have a safe place to store a bunch of spare 8-foot (2.4 meter) long fluorescent tubes in my big garage workshop.

I wanted to make some shelf brackets, consisting of a piece of 2x4 screwed to the wall, with a board sticking out at a right angle.

Pocket holes are very popular. So just for the heck of it, I joined it with a pocket hole joint to see how well that holds...

I took a quick yank at it and the joint popped right apart.

That's a good reason to use better joinery.

I imagine the joint would have held a little better if I had used the Kreg washer head screws instead of drywall screws.

Normally I'd make the tenons using my pantorouter, or my quick-set tenon jig (shown at right), but to show that you don't need a whole workshop full of tools, I'll do this with more basic tools.

I'm going to cut the tenons using my table saw sled, with a plywood box on it.

The box is pinned down on the table saw sled with a block of wood that is clamped to the sled. A shim under the far end of the block causes it to rack a bit, exerting downward pressure on the inside the box, locking it in place.

The workpiece is clamped to the box and the tenons are cut. I flipped the workpiece to do the other side. I normally advise against flipping the workpiece, because any inaccuracy in the wood will translate into inaccuracy of the tenon. But I only had two joints to make.

There was about half a millimeter of waste left on the tenons. I broke these off by hand and cleaned up the edges with a utility knife. If the waste was a thicker, I would have trimmed it on the table saw.

Next I need to cut a strip of wood that is one blade thickness less than the thickness of the tenons. So I hold the tenon next to the fence, and set the fence such that the left side of the tenon is flush with the left edge of the blade.

If in doubt, err on the side of making the strip too thin. If you make the strip too thick, your mortises will be too wide.

I mark where on the 2x4 I want the mortise, also marking how far I should push the 2x4 on the saw to cut just slightly beyond the mortise on the bottom side.

Then I run the piece along the fence to cut the left edge of the mortise. After that, I add the strip of wood between the fence and the workpiece and make another cut.

I square out and cut the end of the mortise on the bandsaw. You could also drill a hole at the end of the mortise (with a Forstner bit), and / or chisel it out.

With glue spread on the tenon and the insides of the mortise, it's time to assemble. If your fit is too tight, you can re-set the fence on the saw to re-cut one of the sides slightly wider.

An open ended mortise can also be called a "bridle joint", though a typical example of a bridle joint would join two pieces of wood with similar cross sections.

Adding a "hook" to keep the light bulbs from rolling off the front of the shelf

Then mounting the brackets above the garage door.

I carried the bulbs up the ladder, two at a time (that's all I can hold in one hand). Quite a few trips up and down the ladder!

See also:

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