Thread: A new joint?
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Old 09-12-2011, 01:20 AM
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Default A new joint?

I'm working on a table that will have stretchers joining the legs diagonally across the bottom of the table. The stretchers will be quite wide (4-5") and will cross at right angles under the table.

I've been musing on a way of having these boards meet under the table. I don't want to do a butt joint, as they're pretty weak. I was considering a joint that I think is a full lap joint - a slot cut half way up/down each board so that they can slot into each other. But that is not the strongest joint, and there's potential for gaps.

So I thought of a joint with mitered shoulders. In the absence of other names I'm calling it a "mitered full lap joint". I'm sure there's a real name for it, I just can't find it (happy to be educated).

I tried cutting the joint in three different ways. First I used some scrap pine, since it's nice and soft and would be easily squished into a light-tight joint:


I had to hammer the pieces together. I can't get them apart. I cut the shoulders using a BCTW Japanese dovetail saw, and then pared out the bottom of the cut with a chisel. I wasn't very happy with the joinery - the slope of the shoulders was uneven, and there were lots of gaps.

So then I tried one where I cut the sloping shoulders with my TS55 on the guide rail, and pared out the waste (and flattened the bottom of the dado) with a chisel:


This one turned out a little better, and I could get it apart (internal views later). I got a better sense of where the joint would screw up - mostly on getting the bottom of the dado flat (the joint is really just a dado with 45 degree sloping sides). So I tried one other method.

The third time I used a V-groove bit in my router, and snuck up on the line using the microadjuster. After cutting the 45 degree shoulders with the V-groove I flattened the bottom with a 1/4" spiral upcut bit. I cut the channel out with the BCTW dovetail saw, and popped it out with a chisel:


I was pretty happy with how it turned out. It's incredibly strong and rigid. It holds together without glue, and has no deflection from 90 degrees. Here's what it looks like inside:




And here's what it looks like half assembled. The two pieces just slide together.


I think this would be a perfect joint to do with hand tools. For instance you could bang it out pretty fast on a JMP with a chisel or small shoulder plane to clean out the waste. Or you could use the V-groove blade on the HP6 with a fence to follow the line, and then use the dado blade to clean out the waste. Or you could cut the shoulders with a shoulder plane resting on a 45 degree fence to get the angle right, and then chisel out the waste.

Whaddaya think?
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