How would you do this?

[James Stokes]

Their are times I need a large solid table. I want to build a table that mounts to the wall. I would like to be able to fold this down when I want to use it. I want a table about 8ft x 8 ft. Here is the problem, I want to put a granite top on it. So I have to either put a counter weight or some type of spring system on it. Also how do I mount the granite so it does not come crashing down when it is mounted to the wall?

[Jim Becker]

James...granite that large is going to weight way more than one or two normal humans can handle. I wonder if you can adapt Murphy Bed hardware for this kind of thing?

[Ian Abraham]

OK.. from the Dept. of Harebrained Ideas...

Mount the table so it swivels on an axle through the centre. Mount the axles on a frame with end stands and put it all on castors. When not in use the table is vertical and pushed back against the wall. To use the table pull it out away from the wall and rotate it to horizontal. Lock the back edge to a rail on the wall ( couple of wingnuts maybe? )

The weight now doesn't matter as it conterbalances itself

I will leave you to work out the finer details... I'm only doing broad and crazy concepts today

Cheers

Ian

[James Stokes]

I am thinking I could mount garage door springs on the floor, run cables up the wall and over pulleys. Then hook the cables to the end of the table. I think that would take care of the weight issue. How would I handle the legs?

I think the murphy bed hardware might work if it will handle the weight. The slab of granite will probably weigh 400 lbs or so. I will have to check in to that.

[Jamie Buxton]

The slab of granite will probably weigh 400 lbs or so.

Granite weighs about 170 lbs per cubic foot. A slab 8'x8'x3/4" would weigh 680 pounds.

I built a queen-size murphy bed using components intended for murphy beds. The platform plus mattress weighed about 175 pounds.

[John Schreiber]

A table like this is a new concept to me so, I'm just thinking aloud here.

Standard thickness for granite counter tops is 3cm or 1 1/4". That means a weight of over 1100 lbs just for the granite. Or if you go with the lighter stuff, it's going to need a stronger backing, perhaps layers of 3/4" plywood. Either way, with legs and support, I think this is going to weigh 1000 - 1500 lbs.

If the pivot point is going to be at the center of mass, the table's going to have to be over four feet off the floor. If it's going to pivot up from an attachment to a wall at one side, the wall will need to be at least eight feet, plus the height of the table, plus room for some strong pulleys tall. When it's being lifted off the floor, it will be supported only at two sides. I'd guess that some kind of engineered torsion box would have to support it.

The ceiling and the wall are going to have to be heavily reinforced. The table legs (and there might be 16 of them) could each pivot. A chain hoist or a winch could be used to lift it up. Springs or counterweights would mean the system is always under stress and couldn't be unhooked.

Sounds like quite a challenge. Why do you need such a beast?

[James Stokes]

I am building a new steel building, The side walls are 12ft so I think I will have plenty of height. As far as why I need the beast, Well I probably don't. I make a lot of differant things that need a large table. I want something that has no give to it, is perfectly flat and something that takes up very little space when not in use. I can get the slab of granite from a friend of mine for about $300. I just want to have the ultimate table.

[Jamie Buxton]

I want something that has no give to it, is perfectly flat and something that takes up very little space when not in use.

If you want something with no give, there are lighter ways to go. Look into torsion boxes. They have a much higher stiffness to weight ratio than granite.

The granite slab itself is somewhat flexible, partly because it is only 3/4" thick. Counter installers regularly bend the slabs in multi-slab installations so that they align. They use nothing more fancy than drywall screws driven up from underneath the granite. That is, even if you use granite for your table, you're going to need a torsion box or the like to support the granite and keep it flat. I'd argue that the granite in that situation adds little except beauty and weight. Beauty can come from other materials -- for instance wood -- that are easier to handle and install.