Q: In carcase and table construction, I often see a lapped dovetail joint connecting a top rail to the legs. Why is this joint preferred over mortise-and-tenon joinery? John Dennis, Temple, NH A: Lapped dovetails are used on a narrow rail above a door or drawer, where there isn’t enough thickness for a strong mortise-and-tenon joint. A kick to the bottom of the leg, or the act of repeatedly sliding the table across a floor, creates racking forces at the top that want to pull the leg away from the rail. The lapped dovetail really shines here, because it has a mechanical advantage over mortise-and-tenon joinery. The angled sides of the tail pull the joint tight and lock it together, which means it can’t pull apart, even if the glue fails. A single lap is strong, but I think a double lapped dovetail, in which the upper rail is joined to the leg and side apron, is stronger. Because a double lapped dovetail requires a wider rail and has two locking joints, it resists racking forces even better. Why small tenons on the top rail are a bad ideaBecause the tenon is in line with the forces working to pull…
Start your 14-day FREE trial to continue reading this story.
Get instant access to all Fine Woodworking content when you try membership today!
In this video, Matt takes some of the lessons learned in episodes 3 & 4 and builds on them to demonstrate the North Bennet Street method for the half-blind, or half-lapped, dovetails on the toolbox drawers.
Become a member today and get instant access to all FineWoodworking.com content!