30" dovetail ????

[Jim Colombo]

I need to join 2 pieces of wood in an L configuration. One piece is 7' x 30" x 3/4" and the other is 5' x 30" x 3/4".

I was thinking of putting a 30" dovetail to hold the adjoining faces but I'm really skeptical about doing that.

Has anyone tried such a long dovetail? I thought of a turnbuckle underneath but think the forces might cause the bottom to be so tight as to pull the top apart.

Any other suggestions?

Jim

[Andrew Seemann]

What are you making? That seems like a rather difficult dovetail to do, especially if you can't do it all in one day and the wood starts to move. Hopefully some other joint would be easier and strong enough. A box joint on a table saw would be easier and as strong, probably stronger.

I remember Frank Klaus talking about dovetailing packing crates growing up in Hungary because nails were expensive, but crates wouldn't be done at furniture quality level.

If you did have to dovetail it, maybe space out the pins so you don't need to cut and fit so many. The more pins you make, the more you need to fine fit and the tighter it will be to glue up.

[Jim Colombo]

I don't have to dovetail, it was just thought and I wasn't thinking of dovetails, I was thinking of one long dovetail along the 30" joining faces.

[Jay Jolliffe]

If you have a router & a slot cutting bit you could use a spline.

[Jamie Buxton]

I'm not understanding. You're joining two wide tops at ninety degrees, with a long miter between them, right? Are you thinking about running the tails and pins at right angles to that miter line? If so, there's going to a whole lot of short cross-grain bits. The joint will be difficult to cut, and may break along those short-grain lines.

One very good way to do what you're doing is a joint connector like this -- http://www.leevalley.com/us/hardware...=3,43586,43588. They're quick to build, and easy to install in place.

[johnny means]

Google "sliding dovetail". I say no because the outside corner on the slotted piece ends up very fragile.

[Matt Day]

If you could tell us more about the project it might help. Is this a project where putting a 2x2 on the inside corner and glue and screw is acceptable? Or is that not appropriate?

At 7’ and 5’, those are some long arms that can put some serious torque on a single dovetail.

[Mark Hennebury]

mitres1.jpg

This is what happens when 30" of wood swells or shrinks in a mitre.

[Dave Richards]

Since you are talking about a 30" long joint, you must not be planning a miter, correct? I'm guessing you are thinking a sliding dovetail like this. As Johnny Means says, the joint would be fragile so you'd need to be able to support the pieces well and not put stress on the joint. Assuming you can deal with that, I don't see why it wouldn't work. Leave the socket slightly shorter than the 30 inches and cut the tail back an inch or so more so the tailboard can move with seasonal humidity changes and not reveal the joint. No glue except for maybe an inch or so at the outside end of the joint. Like so. I might even wax the rest of the joint to make it easier to slide the joint together.

[Jim Colombo]

Thanks Jamie !!!! They would do the job perfectly..

Jim

[Jim Colombo]

You have pictured it perfectly, Dave. The boards are would be sitting on 3 cabinets, so there is plenty of vertical support.

Jim

[Dave Richards]

Jamie's connectors would be easier but where's the challenge? Go for the sliding dovetail.

[Frank Pratt]

Those bolts in conjunction with biscuits or dominoes & some epoxy would make for a very strong & easy joint.

[Jim Colombo]

Looking at Jamie's connectors the smallest would need a 1/2" deep hole. That would only leave 1/4" on the top. I'm afraid that would be a fragile top.

Jim

[Dave Richards]

Jim, although it would only be 1/4 in. thick where the holes are, I doubt that would cause you any difficulty. The diameter isn't that great and you'd only need a few of them.