Not your typical entertainment center - critiques welcome

[Matt Day]

Attached are a couple snapshots of an entertainment center I'm designing (with the LOML's input of course). We're going for a modern, sleek design, and the wood will likely be ebonized black. I showed it in maple for this sketch to make the joints stand out a little more. The speakers are not built yet (I have the kits though), but the unit is sized so they fit as shown. I gave myself 16" deep to allow for a new reciever in the future, and to run cords back there. There will be basically a chase behind the speakers to run wires and have a power strip, and of course a hole in the top to connect the TV, and a hole in the bottom to get power/cable.

I'm estimating the total weight of the cabinet and items will be somewhere around 200 pounds (TV - 55#, receiver - 25#, DVD - 10#, cable box - 10#, speakers ~25# each, wood - 40#). So this needs to be a pretty solid unit.

My rough plan was a french cleat to hang it on the wall, and verticals at least dadoed and glued as shown. My things I'm undecided on and would like some input are:
1) Joints, strong ones - Is a dadoed joint on the middle and ends enough? For the ends should I dovetail, drawer lock joint, box joint, spline, instead?
2) Is using lag bolts on the cleat going overboard? Or is a couple #10 screws per stud okay? Speaking of which, once I put the cabinet on the french cleat, I plan to zip a couple screws in the cabinet part of the cleat, since there's a bit of a lever arm and with the weight of the electronics I wouldn't want it to pull possible rotate the cabinet (if that makes sense).

Anything else that you all would suggest or recommend?

[Peter J Lee]

Looks interesting - I'd make it sturdy as besides the cantilever, there'll be vibration from the speakers. If I were going to float a unit like that, I'd run the power and data up the wall to go behind it. They've got those retrofit boxes that are angled and recessed that could work well.

[Jamie Buxton]

What material are you planning -- solid lumber, plywood, MDF? The joinery would be different for each of them.

[Matt Day]

Sorry, should have mentioned that. I'm planning on hardwood for strength. I'm going to start researching how to ebonize wood which I've never done before, and through that research I may find there's some wood that better than others.

[Phil Thien]

I'm not an engineer, but...

Being only 9-1/2" high, that cabinet is going to want to pry the fasteners holding the cleat right out of the wall.

French cleats are a great way to hang a cabinet. Taller cabinets present a cleat's fasteners with primarily shear forces. So instead of prying them out of the wall, the forces are trying to shear the fasteners off. As the cabinet's height is reduced (or depth increased, or both), the forces involved work like a pry bar, or the claw of a hammer, trying to pull the cleat fasteners out of the wall (or cabinet, or both).

Like I said, I'm no engineer. But I sure wouldn't load 200-lbs onto that unit unless the cleats were attached to both the wall, and the cabinet, in such a way as to prevent the fasteners from pulling out.

[Eric DeSilva]

Were it my entertainment center, I'd probably open up the wall and bolt some support to the studs--probably weld up some 90* supports out of 1" angle iron and arrange them in a way where the steel would be hidden (top inside corners). Then re-sheetrock over them and install the shelf. In the interest of full disclosure, I am prone to overengineer things. But I've got a 3 year old son, and I can just see him trying to hang on the lip of the shelf...

[Steve Baumgartner]

Eric makes an excellent point: you need to think about dynamic loads from people leaning on it, etc., not just the weight of the electronics. I'm also inclined to overbuild things, but I'd be worried about the strength of the cabinet, the strength of its attachment to the wall, and the strength of the wall itself. There's a lot of leverage going on. I think I might use hefty angle irons, with one leg against a wall stud and the other leg out under the bottom of the cabinet, maybe in a rabbet to conceal it. Putting it under the bottom makes the cabinet joinery less critical since it is supported, not suspended.

[Jamie Buxton]

I'd be inclined to use dovetails on the ends, with the tails in the cabinet sides. There's lots of force trying to pull the cabinet bottom from the box, and the dovetails resist that well. They're also a nice decorative touch.

For the middle walls, a dado&glue joint isn't sufficient. (Well, presuming that the wall's grain direction is up-down, like the ends.) Glue doesn't hold very well on end-grain, and that's all that the dado would offer. I'd use dowel joints. I use a shop-built jig like a shelf-pin jig, but it makes 3/8" holes. It gives me lots and lots of dowels, and it ensure that the holes in one side of the joint are aligned with the holes in the other side of the joint. You could also use this for the end walls if you don't want the joinery to show on the ends. It will hold together.

[Matt Day]

Thanks for the replies everyone. I can do dowels for the middle walls, but would a few 2-3" floating tenons be better? I can make them through tenons and expose them if that would add to the strenth.

You're right about the forces involved here, and I know what you mean about shear vs pull out strenth. That's why I was thinking of basically 2 rows of screws/lag bolts - 1 into the bottom of the french cleat, hang the cabinet, then put in the 2nd row of anchors into the actual cabinet part of the cleat. Being about 6' long, there will be 5 studs to attach this too, so about 40#/stud. Do you think 40# anchored with 2 lag screws is too much?

[Jamie Buxton]

...I can do dowels for the middle walls, but would a few 2-3" floating tenons be better? I can make them through tenons and expose them if that would add to the strenth. ...

The basic rule is that glue on end grain doesn't help much. On a 3"-wide tenon, the 3" sides are trying to glue to end grain of the top. That is, the part of the tenon that's really holding the panel to the top is just the little 1/4"-wide face at the end. A single 1/4" diameter dowel has pretty much the same facegrain-to-facegrain glue area. And if you use three of those dowels instead of the single 3"-wide tenon, you get three times more facegrain-to-facegrain glue area.

If you really want to use through tenons, make them wedged through tenons. The wedging gives you mechanical interlocking of the joint, just like the dovetails on the end panels, and you're not relying on glue any more.

[Jamie Buxton]

One other thought... You've mentioned ebonizing. You'll see all sorts of home-brew ebonizing formulas -- steel wool in vinegar, shoe polish, etc. They might work, but no pro shop would bother trying. Instead, they use aniline dye. It works on all woods, every time. Transtint liquid dyes are very good. Buy them from Woodcraft or Homestead Finishing.

[Matt Day]

Thanks for your help and suggestions Jamie. I'll plan on using dowels then, nice and easy too.

Though I've never tried it, I wasn't too interested in doing the home-brew method either. I bought some Fiebing USMC black leather dye and did some test pieces this afternoon. I tried oak, walnut, and maple, all with both WOP and General Finishes Oil/Urethane. After two coats of dye, I liked the maple the best with WOP. The oak looked a little too much like cheap and fake veneer for speaker cabinets. The leather craft store had the smaller bottles for $2 each, so nice and cheap.