Joining Boards on a Curve | How to Make a Slab Table Top
You can ignore those blue chalk lines, that’s just where we would have straight line ripped the slabs. But as you should have gathered by now, there’s nothing straight about this project.
The first step is establishing the curve that will become the edge of the slab. The idea is to follow the grain but keep the curves fair and sweeping, tight curves or too much zig zag will draw attention.
Now that the line is established, Matthew made the first router pass freehand. After the first pass was done, I cut off most of the excess with a jigsaw. If we had roughed in with the jigsaw first, there would have been less support for the router.
With most of the waste gone, a few passes with a patterning bit quickly flattened the edge. However, the curve is pretty rough and has a lot of ripples in it right because it’s based on that first freehand pass. To smooth things out I used a sander to establish a bevel on one of the edges. The 6” pad is wide enough that it doesn’t follow all those little imperfections but creates nice fair curves.
Now the trick is making the rest of the edge as fair as the sanded edge. To do that I set the patterning so the bearing will just barely kiss the top the slab and follow the sanded line. Then it’s just a few passes and the edge is looking much better. There was a little flap left from the gap between the bearing and the cutting edges, but some light sanding cleaned that up in no time.
Before making the template I went ahead and transferred the line to the other slab and roughed it out with the jig saw, just because I wanted a peak at what things would look like when finished.
Just like the slabs, the first thing I do to make the template is rough it out with the jigsaw to minimize how much cutting the router has to do. Then I lined up the template with the clean edge I made earlier and used a pattern bit to copy that profile to the template.
With the template done the rest of the process goes pretty quick. We extend the template over the edge of the slab a bit to give the router some clearance and clamp down the far slab just close enough to remove material down the entire length. The bit is only set deep enough to give enough surface for the bearing of a large template bit to follow. This slab is cut with a 1/4” bit in a 3/8” bushing, so the bit is actually cutting 5/16” from the edge of the template.
Now it’s time to recut with first slab with the template. This cut is made with the 1/4” bit in a 3/4” bushing, so we’re actually cutting 1/4” away from the edge of the template, only 1/16” difference from the other slab, which is how we’re able to get the curves to match so well.
The only thing left is to put in a flush trim bit and flush up the rest of the slabs edge.
Now the slabs are ready to be joined. I cut in some dominos because there was one available at the shop where I was working. But you could also use biscuits or dowels to help alignment.