The Editors Mailbox

The Editors Mailbox

Fight Physics with Lapped Dovetails

comments (5) June 19th, 2013 in blogs

thumbs up 23 users recommend

Small tenons are a bad idea. Because the tenon joining the top rail to the leg is in line with the forces working to pull the joint apart and offers no mechanical resistance to them, youre relying on your ability to fit the joint and the strength of the glue to keep the joint together. An inadvertent kick to the bottom of a leg creates a lot of force up top.
A single lapped dovetail locks the parts together. Angled sides prevent the tail from pulling out of the socket and provide resistance to racking forces in every direction.
A double lapped dovetail is even stronger. Having two tails on a wide rail makes the base even stronger. Use this version of the joint when possible. It will require dovetail sockets in both the top of the leg and the side of the apron. Youll also need to incorporate a wider top rail.
Small tenons are a bad idea. Because the tenon joining the top rail to the leg is in line with the forces working to pull the joint apart and offers no mechanical resistance to them, youre relying on your ability to fit the joint and the strength of the glue to keep the joint together. An inadvertent kick to the bottom of a leg creates a lot of force up top. - CLICK TO ENLARGE

Small tenons are a bad idea. Because the tenon joining the top rail to the leg is in line with the forces working to pull the joint apart and offers no mechanical resistance to them, you're relying on your ability to fit the joint and the strength of the glue to keep the joint together. An inadvertent kick to the bottom of a leg creates a lot of force up top.


Lapped dovetails are the right joint for a top rail

For a lot of woodworkers just getting acquainted with the intricacies of dovetail joinery, the idea of using a lapped dovetail to join the top rail of a carcase or table to the adjoining leg seems like overkill. Why not just use the tried-and-true mortise-and-tenon? A recent Q&A in Fine Woodworking magazine highlighted this very topic, and it's worth some thought. A mortise-and-tenon might last you a decade, but a dovetail will likely last you a lifetime.

 

Q: In caracase 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, New Hampshire

 

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 points, it resists racking forces even better.

- Steve Latta is a contributing editor



posted in: blogs, joinery, dovetail, latta, Q&A, lapped dovetail, furniture construction


Comments (5)

Brundo Brundo writes: I build a writing table long ago utilizing small tenons. And it has shown how wrong it was. My intension is to fix it as suggested above. But I would love if there is video showing how to do it. 1.5" square leg has not much room to install dove tail joint.
Posted: 2:56 pm on July 11th

trojanhorse trojanhorse writes: I know it is woodworking heresy, but using one or two screws from the top down through the mortise/tenon will also do the trick. Once the top is on, the fasteners will never show.
Posted: 10:31 am on June 28th

gewima gewima writes: A question. Would pinning the mortise and tenon match the performance of the lapped dovetail?
Posted: 10:05 am on June 27th

Ed_Pirnik Ed_Pirnik writes: Tim: NICE point!!
Cheers,

Ed
Posted: 8:54 am on June 26th

Tim_38 Tim_38 writes: It's not a case of fighting physics, but of using physics.
T Caveny
Posted: 6:37 am on June 22nd

You must be logged in to post comments. Log in.

Advertise here for as little as $50. Learn how

Save up to 51% on Fine Woodworking

 

Become a Better Woodworker

ABOUT THE EDITORS MAILBOX

FineWoodworking.com editors report from the woodworking front lines. Check in every weekday for news, information, projects, and answers to questions from Fine Woodworking readers everywhere.

Learn about our new format!

Archive: Temporarily unavailable. Stay tuned and sorry for the inconvenience.