Solid Wood Tables — Span Length Limits
How long is too long for a maple table? The discussion moves to apron depth and thickness, steel reinforcement, a center rib, and box panel construction. April 20, 2011
Question
I have a client that wants a 130" maple dining table. The top will be 1 1/4" thick. How long can a table be without requiring a center support? I am using 5 1/2' farm legs and the side aprons will be 110" long down the side.
Forum Responses
(Furniture Making Forum)
From contributor G:
The height of the side aprons will determine the max length. Taller ones will support more. There is no doubt an engineering formula, but why not try a test? Set up a 110" long side apron and put some weight on it and see the deflection and decide if it is okay.
From contributor N:
A side apron that is too wide will limit the leg room under the table. A side apron of that length might mean thinking outside the box a little, and require you to think of a way to install a 110" long piece of steel to the back side of your apron or sandwich it between two pieces of wood so you can't see it from under the table. That would make for a heavy table, but it could work.
From contributor J:
I agree with contributor G. There won't be a hard and fast rule because a long table is more likely to flex and sag unacceptably under load than it is to break, and the amount of flex/sag one can accept is somewhat subjective.
I have done some simple engineering calculations for extension tables I've built, but it's tricky. If you know the species and all the dimensions of both tabletop and aprons, then you can make a decent calculated guess as to how much it will deflect under a load of X pounds at a given point, or N pounds distributed evenly over the surface, but it's not a simple calculation.
For both the top and the aprons, height is much more meaningful than width. A member that is twice as wide (horizontally) will carry twice the load. A member that is twice as tall will carry four times the load.
From contributor W:
Besides just the side aprons, how about adding 2 or 3 ribs down the middle, out of sight?
From contributor G:
There is just such a table in the Project Gallery:
Maple Dining Table
Top is a bit thicker, but would weigh more, so that may be a washout?
From contributor N:
You can only make the aprons so tall, but you are not limited on their thickness. An 8/4 or 10/4 rail will be a lot stiffer than a thinner rail. Steel angle always works too.
From contributor E:
"Too big" is not really a big problem, until you've built it and can't get it through the door. I've seen some enormous worktables built like engineered boxes that were flat after several years of hard shop use. Fairly light too.
From contributor V:
I agree - "too big" only matters when compared with the surroundings, or as he pointed out, the door it is going to go through.
From contributor F:
I agree with contributor W. We do a lot of tables that are greater than 9 or 10 feet. I assume this isn't a trestle, otherwise a beefy center stretcher would be an easy insurance answer. Otherwise the thickness of the aprons can also help you with long term sag.
From contributor I:
I'd feel a bit better with a thicker top. A center rib would help a lot, and depending on the width it is likely out of reach of people's knees. If it's the deepest rib you could thin the ends for the comfort of the people sitting at the ends.
I would also test the design - use the same species at the size you are considering, prop up the ends, and put some weight on it. See how it feels to you. Develop your sense of strength.
From the original questioner:
Just wanted to thank everyone for their answers. We are going to make it with thicker aprons backed with metal supports and a center rib.
From contributor P:
I think there's no problem with the table. Having a big table isn't a problem unless your kitchen is out of space.
From contributor C:
I've built 48' long by 5' wide maple conference tables (birdseye) with corebox construction that had normal apron and leg dimensions. This will work if the customer is not demanding solid wood. Much lighter than solid tables and just as durable.1/4" book matched skins with 3 1/2 core, 4" thick all together. Solid bullnose edge.
