Engineering a Wide Pull-Out Table

Furnituremakers puzzle over ways to construct to a wide-span, narrow table able to roll away from the wall as needed. November 3, 2010

I am an interior designer who would like to specify a table top that is 6'-7" long x 15" deep x 2" thick and is mounted on legs at the two extreme ends of the table top that are 36" high x 15" deep x 2" thick that are on wheels. The intent of this table is to slide in and out over the top of floor mounted shelves. Will a span of 6'-7" x 15" x 2" attached to end mounted legs sag if constructed of some variety of hardwood, like birch? Would MDF work? Would plywood work?

Forum Responses
(Furniture Making Forum)
From contributor W:
A torsion box would work. No solid wood will.

From the original questioner:
Thanks. What would be the specs for a torsion box of these dimensions?

From contributor W:
I could tell you about the ones that I have built for similar spans, but it would be best if you talk to an engineer or the cabinetmaker who is going to fabricate the table.

From contributor J:
Disagreeing with contributor W a bit, a six and a half foot solid wood plank 2" thick could be quite strong. Engineered sheet goods like MDF and plywood might not fare so well, but most species of solid wood would be fine in terms of sagging/load bearing capacity. That said, a solid wood top would be heavy, and potentially dangerous on such a narrow base. A torsion box is the way to go to keep the structure light and easy to maneuver.

From contributor W:
You might be right, contributor J, and given a bit of clever engineering, say a hidden piece of angle iron in the middle, it could definitely be done with solid wood. I guess I was thinking there would be a load on the table. No load, no problem. White oak might be good, ash, walnut, maple - those would work.

From the original questioner:
Thanks for your insight and experience! The table can be wider, but not narrower due to the fixed width of the shelves below. Regarding the narrow base, how should it be made more substantial/dimensions changed if a solid wood top is used?

From contributor P:
15" wide x 2" thick x 78" long? Guys, that's not going to sag at all if made of solid wood. It will be heavy, though, and tippy if you are trying to roll it around. Why not have a pull out in the lower case? Do you need to move this table around the room?

From the original questioner:
Thanks. Unfortunately, the upper and the lower shelves already exist, so I don't believe a pull-out is possible at this point, but perhaps I am not being creative enough. The intent is to pull out the table just past the shelves to have a working surface for reference material stored above and below, not to roll the table around the room.

From contributor T:
I would split the width into 2 or 3 and make a very short drawer with heavy duty slides. Set the boxes directly on the bottom cabinet and screw through the back into wall studs to make sure they will not tip up.

From contributor G:
With a little redesign, you can mount that slide out desk on a pair of drawer slides at either floor or shelf height. At shelf height, have an angle iron ell welded up to bolt to the wall and carry the shelf (no legs needed). Or skip the angle iron and use the legs to carry the shelf slides.

The other option is to add an end cap to the existing shelves (floor to ceiling), which would provide a support to slide the shelf in and out, again on conventional drawer slides. With no triangulation, unless you hide some steel in it, it will want to collapse to the left or the right.

From the original questioner:
Thanks for presenting the alternative approaches!

From contributor I:
I agree, the span is no problem in solid wood, though it will be tippy in the 15" dimension. That said, imagine using a hollow core door - your basic torsion box in its most common form. You'd need a thicker, more durable top, and some way to brace the legs (steel, stretcher, corner blocks, or extra thickness).

If I were unfamiliar with this construction, I'd find someone to work with who is familiar. Go over the design with them and they will do the engineering. Don't bid it out - that's bad form unless you pay for their time (and announce your intention up front). The payoff for you is a working relationship with a local craftsman, who can assist you on future projects.

What you are asking is not that difficult if you know what you are doing, but balancing all the design issues takes a lot of emails and is easier in person.

From the original questioner:
Thanks - valuable input! I have also become concerned about the tipping possibilities and therefore I am also presenting a drop-down work surface alternative versus the roll-out table.

From contributor I:

Note also that the rolling version is easiest if you use wheels, not casters. Casters trip over themselves when they reverse direction, a major cause of tipiness.

From the original questioner:
I did not know that. Thanks again!