Well, I might as well start this journey.
Cross Lap with Mitered Corners
I have, as yet, been unable to find any written reference to this joint. I have seen an example of it from two sources. One being a video by Jay van Arsdale where he shows an example and Chris Hall has utilized the joint in a couple of projects that he has posted about on his blog, here for example.
The joint looks simple, but the addition of the mitered corners increases it’s complexity more than I anticipated. The mitered corners also adds a great deal more strength to the joint than I had anticipated as well. Even poorly executed examples, riddled with gaps, were quite rigid and resisted torsional loads and required a mallet for disassembly. An addition advantage of this joint is that the long corners of the work pieces can be chamfered, up to the depth of the miter, before final assembly. The mitered corners automatically create the appearance of an internal miter and gives the impression that the pieces wrap over each other.
I chose to execute this joint in material that is square in section. It simplifies the layout and also happens to be what I typically use for my “post and panel” type projects. The joint could be used with material of differing section profiles, but the layout becomes more complex due to the varying angles of the miter. In square stock, the miter is a plain old simple 45°.
As noted in my drawing above, the offset distance (O) that creates the inner square and miter, can be any distance of your choosing. Considerations should be made for any additional joinery that may take place. The insertion of a pin or a thru tenon from an adjoining structural member. As in a corner joint where the third piece would tenoned thru the cross lap and wedged. Thus locking all three members of the corner together.
When I cut practice joints I do so with as little aid from knife lines, gauges and jigs as possible. I lay out the joinery with a square and ink. Saw and chisel to the lines to the best of my ability. My rational is that my skills will be strengthened on several levels. My layout ability, sawing and chiseling should all improve with each practice joint done in this manner. For actual project work however, I’ll utilize all manner of aides at my disposal.
The layout is fairly simple on this square sectioned stock. Both pieces are identical in their layout. Please overlook my smeared ink lines.
One thing to keep in mind with this, and all joinery, is preservation of the layout lines. What I mean by this, is that the joint should be cut in a way that preserves the layout as long as possible. Three faces of each workpiece will have material removed. This needs to be done in such a way so that you do not lose the depth line for the lap before that section of material is removed.
To start, I sawed to the depth lines on all three faces of the layout.
Then I removed the center section that creates the lap portion of the joint.
The rest is chisel work. Carefully paring to the layout lines. The miter should be a tight friction fit. Too tight and you run the risk of one splitting out material at the mating corner. The center section can be as tight as you dare make it. Since the compression in this area is against the end grain, there is very little chance of a split or fracture. You do need to pay careful attention when making this joint close to the ends of a workpiece. There is a danger of splitting off the section between the joint and the end of the workpiece. Always cut a sample joint in the material you plan to use so that you can get a feel for the compression rate. Soft woods can compress quite a bit. Hardwoods may not compress at all.
My first four attempts at this joint failed miserably. Gap after gap after gap whenever I assembled the joint. My material is from 2x construction lumber and compresses a lot. So I found it best to leave all of the layout lines intact when sawing and chiseling. I also found no effective way to saw the miter. You can’t just saw across the diagonal since you need to leave the layout line on each corner. At any rate, I had far better luck paring the miter.
My layout for depth looks a little off.
What it looks like with the layout lines removed.
With a chamfer added to the long edges.
Joint #5 came together acceptably well. There is still a lot of room for improvement, but I’m getting there. Another twenty or thirty practice joints and I may begin to feel comfortable with this joint.
My gallery of gaps and shame.
This joint is a keeper and I can already think of ways that I can work it into furniture projects. It is a challenge though. A 45° paring guide will prove quite useful when it comes time to put this joint to actual use in a project.
I hope that you at least give this joint a try, if for nothing more than the challenge. Who knows, you may find a use for it too.
Greg Merritt Part 2