Help with making a support for a wood slab counter top

[mf44]

Hello all,

I've got a very large slab of maple, with a live edge, that I'm looking to turn into a counter top in a large bay window area.

Essentially, the opening is about 12 feet long, the slab spanning that will be about 2.5" thick, and about 2 feet deep. The area where I am mounting it has plenty support on either side and on the back, but I want to avoid any support underneath the slab, so I can have seating there.

I was thinking I could make a lattice work of metal square tubing to span the length under the slab and support it, without needing any support directly beneath. This lattice work could be supported on both ends, and on the back end. Then I could just drop the slab on top and bolt it up.

My question is, since I'm not much of a metal worker, how big do you think I need to go on the tubing to make sure I have the strength to support such a big honkin' piece of timber, without sag? Can I just use 1x1 tubing, assuming I have a number of cross members? Or perhaps a larger tube for the front of the span, since that will be the area with the least support? And how many cross members should I be using?


Any help is appreciated, thanks!

 

[Kevin54]

What about just making a frame out of 2x4's. I didn't want to have any legs to my bench, so I made a square frame in which to mount my bench top, and used 2x4's with a 45 degree angle on them back to the studs in the wall. The bench will hold a heck of a lot of weight. My wife and I both set on it to test it out and in never flexed at all and I weigh in at 250#. I don't have a picture of the framework for my long bench which is 21' long and only 5 supports, but I have a pic of my desk which I have also set on to try it out for strength and it only has two supports.

 

[MoonRise]

First off, sounds kind of cool.

Next, what type of maple? Because 'maple' (hard maple vs soft maple, etc) varies in its physical properties (weight/density, strength, etc).

Also, is the maple dried already? Because a slab of solid maple 2" thick x 24" wide x 12 ft long is a rather big chunk of maple and will take a rather long time to air-dry (2+ years). Just an FYI if you didn't consider that.

The project sounds 'do-able', but just putting a frame of 1x square steel tube with 14 gauge walls is probably not going to be strong enough to support a fully cantilevered 12' long slab of maple.

Cause someone, sometime, is probably going to sit or climb up on top of it. Or more than one 'someone'.

And putting ~500+ lbs in the middle of a cantilevered 12' long x 2' wide slab of maple is asking a lot from the mounts/mounting.

Generally, you will want to 'fix' that slab to the end supports and to the back support so that the slab (and its possible support frame) can not really sag/flex freely and instead will attempt to transfer the vertical loads into tension/compression loads. And your frame/mounts will have to be able to support not only the vertical loads but also the bending because the load is not 'centered' over any vertical support structure.

If you put just a single support post/column in the mid-span of your 12' long slab and the loading gets much 'easier' to handle.