Multiple Half-lap Jig for Grid Work

Question

I'm making a gate from 2x2 material. I want to build-in a half-lap grid. I came up with a jig to use with my router that involves laying the 2x2 side by side in a box 1 1/2" deep then attaching at 90 degrees, a series of 1 1/2" template pieces with a 1 1/2" space between each template piece. As you can see in the photo, I'm able to get results but not consistently enough for my needs. I would like to do this on the table saw with some sort of jig similar to a finger joint jig but would need to make two cuts per crosscut. An inch and a half dado set would be perfect but not an option. Maybe using such thick material makes a jig impossible. Any input would be appreciated.

Answer 1

So to start by clarifying the issue...if you have a normal finger-joint jig with a stop block the same size as your dado stack there is no way to reference the first cut on each board. Since the stock is wider than the dado stack you'd need two passes, one for the "leading" edge of the half-lap and one for the "trailing" edge. Once the first dado is made on each board you can make the next dado by aligning the stop block on the two sides of the previous dado.

I think the solution will be to have a second, movable reference block whose width is the difference between your stock width and your dado stack width. You'll then make your first cut with the new block set against the jig's stop and the end of the work piece against the new block. Then your second cut with will be with the end of the work piece against the jig's stop. (Note that for this use of the jig the jig's stop should be the stock width plus the new block's width away from the blade.)

For example, say you've got a 3/4" dado stack and your stock is 1" wide. You'll need a stop block 1/4" wide. Your first cut (with the new block) will be from 1" to 1 3/4" from the end of the work piece, and the second cut (without the new block) will be from 1 1/4" to 2" from the end of the work piece. (I'm not using your exact dimensions because I think this makes it clearer what is happening...)

Answer 2

I did something similar to make book shelves for paper backs.

For a given set, I clamped all the verticals together, then made two passes with a radial arm saw to define each side of the cut. Did the same for the shelves. Took out the wood between with a chisel. Since the baseof each cut was buried in the joint, I didn't care if that was rough. My shelves weren't designed to have shelves flush with risers. I wanted to use 1x4 material (3/4 x 3.5) and a paperback is about 5" wide,so the shelves were proud of the risers by 1.5"

You can define the edges of the cut with a regular saw blade, then make a series of passes with a dado to clean out the middle. Make a few extra pieces during the first stage, so you have test pieces to dado.

Answer 3

The jig you want for this looks like this

There is a set screw on the end not shown on the picture to set the thickness of the saw blade (done once when you make the jig). When using the jig you just clamp around the piece that you want to cut a groove for and that's it for setup. No calculations, just using the jig's two different lengths as end stops for the inner/outer cuts and then rip away the waste in between.

There is a build description on this web page and a corresponding video.