Floor standing U wood frame built at home - what to use for a 90 degree joint?

Question

I'm building a U frame (inverted U). So it will have two side pieces, and one piece sitting at the top of these sides.

I plan to use a 3/4" melamine that is 4 inches wide. It is white melamine on both sides, but the edges are not.

The sides would be 58 inches tall each, and the top is 70 inches long.

It will look like a console table, but this is not a table, just a decorative frame. I might include another piece of wood in the center if it sags due to the length.

I will do this at home, I don't have special tools (I have a drill, rotary tool, screws, etc. but not mills and other bigger/heavier tools).

How should I make the proper 90 degree joint between the sides and the top? I'm wondering if the glue will work since one side is melamine but the edge of the side where it will seat is not. I would like to avoid using L brackets because they would be visible if you look underneath.

Based on the thickness (3/4") and the material (melamine on both sides, but not on the edges) what would you suggest to use? Wood screws? Wood glue plus nails? I'm not sure if wood screws would damage the wood since it's just 3/4". Should I still consider L bracket? Two or just one per side?

I appreciate recommendations!

Answer 1

As described, there will be huge issues with racking - the tendency for this to want to collapse onto one leg or the other, no matter what fasteners are used.

If you'll take a look at any flat pack furniture, you'll see that they come with a back, often nothing more than cardboard. One might think that the back is provided to keep things from being pushed off the back of the shelves and falling behind the cabinet, but the back is really to prevent the whole thing from collapsing sideways. The fact that it keeps you from pushing your shirts behind the wardrobe is just a bonus.

If you were able to find flat angle brackets:

^{Image courtesy of walmart.com. First somewhat small image I found for what I was after.}

that were long (I'd suggest 12" legs or more), with legs that were only 3/4" wide so that they would hide against the edge of the particle board, then attach them with screws designed for particle board, you might have enough rack resistance to get this to stay upright for a while, but it will still want to sag and warp eventually.

You're going to need serious corner bracing (straight pieces or triangles that connect the top to the legs at about 1/3 the length of the top - roughly 20" across and 20" down) or something like a shelf support bracket or a full on back in order to keep this from collapsing.

Answer 2

A nearly 6 foot span of melamine that isn't supported at all in the center is going to sag eventually if you do this without adding any type of bracing. At that size, the "legs" are going to have stability problems too and that is going to get worse as the top starts to sag. You don't mention what, if anything, will sit on top of this structure, but adding any weight is going to hasten these issues.

If you could add a leg in the center that would go a long way towards reducing any sagging that might happen. adding L-brackets might help a bit, but in the end most of the center section is going to remain unsupported and eventually develop problems.

One solution that might help is to add "ribs" across the bottom of the spanning member, although at 4" depth, it might be hard to do this without throwing off the proportions of the finished piece (which I am assuming is sized as it is for a reason).

As far as how to finish and attach the edges, I can think of 3 options:

Mitered Edge

the best looking option would probably be to cut 45-degree miters at each mating edge and glue-and-screw them together, but you'll need a table saw to do a decent job of that. This will give the cleanest final appearance from all angles of view.

Do it like Ikea

The next best option is to sit the top member on top of the legs, like a table. Then you probably won't need any glue, and you also don't need a saw. The downside of this is that the unfinished edges of the melamine are going to be visible from either side, and it will look pretty ugly from the front. If the edges of your boards are finished, or if you have a way to finish them later (like paint), it might look good if you oversize the top by a few inches to give a "lip" over each leg. This would also provide extra options for bracing and stabilizing the whole contraption.

If you look at a lot of Ikea furniture, they often use this type of joint and what is called a "cam lock" connector: the edges attached using pins that protrude from one part into a pre-drilled hole on the other and then secured with a special locking nut.

"Don't try this"

The worst option is to try and suspend the horizontal top on the inside of the two legs. This has a lot of pitfalls and I would suggest you not try it.