I am designing and will be building a diningroom table. We want to have maple around the edge and tile in the middle. This will obviously be a little heavy, and want to build in sufficient support that it won't sag whan it's loaded full of food and an elbow here and there. I also don't want to build it too strong - thereby adding lots of excess weight to the table.
Can anyone point me in the direction of a website that lists strengths of various dimensions of lumber?
How much load a 1x3 could bear, max length, where the legs need to be, how much overhang and so forth. (Not just for 1x3s, but a chart with various sizes, so I can figure out what I'll need.)
I seriously doubt there is any one resource that will provide the info you requested. There are several sites that provide load capacities for species of wood but mainly for the construction industry. There is a site that will show you span tables for specific woods (thickness and widths) especially for making shelves - but for table making, I think you're on your own.
You didn't state what style (round, center pillar, apron frame, legs, etc.) or size table. A 3/4" ply underlayment for the table section where the tiles will be may be way overkill depending on the type of tile and size of table. If you're using 6" squares (or there about) then they will lend some rigidity to the top and you would not need as much cross-bracing underneath to prevent sagging if you use thinner material. I would be worried more about when people lift the table by the edge to move it and flexing a section which could cause a grout line to crack. So a design that takes that into account would be wise. Edging or bread-boarding all around with say 2" or 3" width of hardwood that is secured to the underlayment will help prevent any flexing of the tile field.
Just about any underlayment you decide on will need cross-bracing just to keep it flat over time even if it had no tiles installed on top.
Some of these sites may have some helpful info or lead to another site that would be more specific:
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maple around the edge and tile in the middle. This will obviously be a
Caryolyn As a suggestion there are many stores selling such table's, Peir 1 comes to mind and there are many others. Take a look at them, No clerk is going to object to you looking underneath the table, Hell you are just trying to ascertain whether it will be strong enough for the kids to jump up & down on it . From that you can expand or subtract to the size you are looking to build.
The critical area to keep from deflecting is the field of the table with the tile on it.
About ten years ago I built a marble tile topped dining room table about eighty inches long and about forty inches wide. I used 3/4 marine ply for the substrate and thinset the tiles to this.
I used three inch wide hardwood for the apron . Between the aprons I ran two and one quarter inch wide strips of hardwood ply every twelve inches, with short strips butting into these at ninety degrees, on the centerline.
These strips were biscuit joined into the apron and the ply substrate and the top edges were glued to the ply substrate. Then I applied a one half inch thick ply with glue to the underside. This turned the substrate assembly into a kind of space frame.
It may seem like overkill but the space frame construction allows people to lift the table without flexing the substrate to the degree that the joint lines on the tile would crack.
Even with this construction it is important to use a flexible grout. The grout will need to be sealed in order to resist staining.
This table had a hardwood surround. If you go this way you should prefinish the wood, paying particular attention to the edge that will butt up to the tile. By doing this you will avoid having the grout bleed into the wood.
The people I built this table for still have me over for dinner once in a while and there are no crack lines in the grout.
It is heavy. I don't think there's any way around that. Ceramic tile in three eights thickness is about four pounds per square foot. My table was about twenty two square feet, so there is about eighty eight pounds of tile involved.
Good Luck.
Regards, Tom Thomas J. Watson-Cabinetmaker Gulph Mills, Pennsylvania
How big is the tiled area compared to the table? If it's only a bit in the centre (thinking of some Scandinavian-style designs I remember from decades ago) then would it make sense to make that bit "float" in the centre so that the table flexes independently of the tiled portion?
Obviously not an option if the tiled area is most of the table surface.
Your concern here will be stiffness, not strength as the table will sag excessively long befor it breaks.
The phenomenum you need to analyze is _strain_.
The analysis of stress (how much it takes to break soemthing) and strain (how much something bends under a given load) is fairly simple for a simple shape like a floor joist and gets more complicated as the shape gets more complicated. For your table you'll need to know the tensile strentgh and Young's modulus for maple which can probably be found. But then you'll need to model the table as if if were a beam or a plate supported at it's edge. There is a handbook by Roark (I think) that a civil or mechanical engineer could use to do the analysis for you.
Someone could put together a chart for table design similar to what is used by architects to size floor joists, but I doubt that anyone has.
The good news is the stiffness of a beam goes up with the cube of the vertical dimension of the beam. So a 1 x 4 apron will be almost three times as stiff as a 1 x 3 apron. This means that you only need to overbuild the table a little to get a big margin of safety in your favor.
A table apron is essentially a beam supporting the tabletop much like a floor joist supports a floor. So if the span of the legs is long enough to compare with floor joists in an architect's table for sizing floor joists then you can get some idea. Maply will probably be stiffer than the stiffest wood in the tables, but not by a whole lot. Two 1x4 table aprons on a table 24" wide will be about as stiff as a 2x4 floor joist on 24" centers. If the legs on the table are sized to look proportionate to the table they will probably be more than strong enough. Only if you want real spindly legs should you have to worry about them. The amount of overhang is also going to be a matter of taste and convenience. Unless you design a pedestal table any aprons that will support the middle of the table will handle the overhang easily.
The problem you are addressing is not trivial to analyze, but it is almost trivial to just wing it. For instance, you could just take a piece of 3/4" plywood the size of the tabletop you want, support it between two sawhorses on a couple of cheap 1x3s stack weight on it equivalent to what you want the table to bear and see how much it sags (or if it breaks). Then replace the 1x3s with 1x4s and so on until it is stiff enough to suit you.
Substitute the same sized maple aprons in your finished design and with everything rigidly joined you should have a nice factor of safety.
Or just look for a table like the one you're making and see what they used....
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