Floating shelf fireplace mantle

[Zahid Naqvi]

I read through several discussion on this topic at SMC, and consequently discovered the Rockler and LV hardware option. I have a few question about the strength. I am planning on replacing the existing fireplace mantle with a floating shelf. It will be about 4" thick, 10" deep and 70" wide. The construction will be your typical torsion box. Considering this is slightly bigger than your typical display shelf, I am not sure the LV hardware is appropriate. With the 4" thickness I think I can get away with french cleats but the depth of the mantle makes me queasy. I have used french cleats to hang cabinets and it works great for that purpose, mainly because there is a lot of vertical force in a cabinet, in case of a shelf most of the force will be torsional (pulling) for which the french cleat is not ideal. I was thinking something like the picture below

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The question is will screws drilled into endgrain be strong enough to hold 30-40 pounds of weight. I suspect some of my wife's prized glass collection might go on this and any "accidents" will have serious implications for my fledgling hobby :eek:.

[Greg Cuetara]

I made some floating shelves in our house a few years back. All I did was attach a 2x onto the wall then push my floating shelf over it and screw from the top into the 2x. Seems to be plenty strong for the stuff the LOML has decided to put up there.

My opinion would be to make a prototype, which would not be that difficult then attach to your shop wall and put some weight on it and try some different methods till you find one you are comfortable with.

Greg

[Rob Fisher]

With 4" to work with I would think about opening the wall up and attaching supports directly to studs if you are concerned about weight. The shelf can cover the hole in the wall. If opening the wall is not an option I would attach a built up frame like you show, pocket screwed or toe screwed, not screwed into end grain. I would also beef up the piece that runs along the wall, +\- 2x4.

[Sam Murdoch]

Rather than that ladder thing you are showing with all the deficiencies of end screws and minimal glue surface you would be better off stealing 1.5" x 3" to 4" x 66" long (this could be 3 or 4 segments if the stud layout behind is adequate) of the inside of your shelf for a straight and flat piece of blocking lagged into the studs as Greg and Rob are both suggesting. If you anticipate the need to remove the shelf some day you could screw up from the bottom into the cleat and the top portion of the shelf (or through bolt) - otherwise just glue it on and leave it for the next generation :)

[Zahid Naqvi]

the 2x4 will be attached to the wall studs through screws. I have heard people making the torsion box with the skin extended a couple of inches and either gluing or screw/nail it to the 2x4 attached with the wall studs. The image above is a slight variation of the same concept. So Greg what did you use for the shelf, did you make something like a torsion box or was it solid wood. I am not sure 1/4" ply will be strong enough to hold a shelf like this using screws, it might rip. Then again I guess testing a prototype is not that expensive to begin with, maybe I should do that.

[Jeff Monson]

If you are worried about strength, why not make a torsion box, screw and glue 1/4" or 1/2" plywood to the top of the box. Attach to the studs from the exposed underneath, slide your floating shelf on. I think a top skin would add more than enough strength.

[Van Huskey]

I think it is hard to argue the prototype approach, you can safely static load it well past your design needs and also dynamically load it to account for accidents. In the end I might load it to failure just to see how much it would hold AND the mode of failure.

[Greg Cuetara]

Not that this is the greatest picture but this is what I did.

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It is 3/4" red oak top and bottom. The sides and ends are 3/4" RO also that I put a rabbit in and then glued it up. I put a few spacers in between. I put a 2x cleat on the wall with 2 - 2 1/2" screws into each stud. If you are concerned you could always use lags like Sam suggested.

All I did to attach it was to screw from the top into the cleat and then walked away. I think the biggest one is about 48" wide and sticks out about 8". Mine are 3" thick so with 4" you should be able to get something to work. I would be a bit hesitant to use 1/4" ply...but maybe that is just me because i overkill everything (ie i use 1/2" ply for drawer bottoms).