Furniture made from wood slabs with natural edges still intact has a soulful, sculptural quality, thanks largely to the handiwork of Mother Nature. And creating projects with waterfall joints—a miter joint with the continuous-grain appearance of water going over a falls—only adds to the beauty. But cutting tight-fitting, precise miters on stock with no straight reference edges and then gluing the miter together can be tricky. And, of course, you’re not making a four-sided frame so conventional clamping techniques aren’t going to work.
Here are some pictures and links for instructions on how I crafted side tables for The Sawyers House available at https://www.vrbo.com/1744359?noDates=true&unitId=2305861
Flatten and stabilize the slab
Your natural-edge slab will likely have rough-sawn faces and bark-covered edges. In order to create perfect-fitting miters, though, both faces must be flat and parallel. You can achieve this by running the slab through a wide planer or drum sander, but if that’s not an option, use a router and shop-made jig. This requires patience as you make repeated shallow passes across the width and along the length of the slab, but it’s effective.
Miter the waterfall joint
Because you can’t use a tablesaw, radial-arm saw, or sliding mitersaw to cut the miters, I used a portable circular saw equipped with a 60-tooth blade and a simple straightedge jig.
Set the circular saw for a 90° full-depth cut, and trim one edge of the jig to provide zero-clearance support. Position that edge on the cutline, clamping it as close to perpendicular to the slab’s edges as you can by eyeballing it. Then cut across the slab.
With the slab now in two pieces, tilt the saw blade to 45° and trim the other edge of the jig for zero-clearance support. Reposition the jig on the slab’s top face with the mitered edge aligned with the tip of the just-cut end of the slab, clamp it in place, and make a miter cut.
Strengthening and gluing the joint
Regardless of whether you’re making a table, desk, or bench, it’s crucial to strengthen the miter joint beyond just glue. Do this by concealing a loose tenon or two in the joint. This also helps align the joint.
For gluing the joint I used clamping blocks as a temporary addition, allowing me to clamp wood in a spot you might not otherwise be able to get a clamp. The drop off of the two 45° cut above will have the perfect angles for this purpose. Keeping in mind clamping blocks are a temporary addition, we need to be able to get them off later. That’s where the CA glue comes in. It’s plenty strong for what we need to do here, but we’ll be able to easily remove the blocks after the joint is glued up.
Drawing the joint close
With a well-executed miter it shouldn’t take much to close the joint. A clamp on each block will be sufficient. Take it easy as you tighten the clamps, working your way across the miter. Once the glue dries remove the clamps and knock the gluing blocks off with a rubber mallet.
https://www.woodmagazine.com/woodworking-how-to/joinery/waterfall-wonder