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I am trying to build a cherry table. I will be creating the top out of multiple 8/4 boards using standard techniques. The table will be 42" wide by at least 68" long. I have come up with the idea to not use aprons.

My question is how should I stiffen the table without having the aprons for support?

My ideas so far:

  • Use a router to create one or two grooves almost the entire length of the table (making sure that the groove is in only one piece of wood), then insert a "spline" along that length that will be 4/4 stock; basically a long mortise and tenon to attach an apron in the middle of the table. I figure if I glue this in, it will strengthen the table length-wise and not cause problem due to wood movement because the groove will run with the grain. I would probably do this several times because I don't want the "apron" to stick out from the bottom too much, so it would not be super thick

  • Do the same grooves but instead epoxy in metal splines

  • Don't do anything to strengthen it lengthwise, because 8/4 cherry over that length may just be strong enough?

  • Attach wood strips across the grain using cleats to strengthen table across the width

  • ??

I'm looking for any good suggestions/critiques here. Googling has lead me to believe that nobody really does this, but I've seen huge tables with only the 4 legs for support, so I'm guessing it can be done.

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    How many legs and where are you placing them? – bowlturner Jun 1 '15 at 12:44
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    How will you support the table? Legs, pedestal, trestle...? – Caleb Jun 1 '15 at 12:44
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    What's the difference between your "spline" and an apron, other than distance from the edge? – Caleb Jun 1 '15 at 12:45
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    What's the purpose of the grooves in which the spline sits? The splines probably don't need the lateral support that being set into a groove would provide, and you'd essentially be making the top weaker along that point. – Caleb Jun 1 '15 at 13:39
  • @bowlturner 4 legs, all at the exact corner with no overhang at all. – kannon19 Jun 1 '15 at 16:00
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The apron on a four legged table serves a number of functions, and you may not have considered them all. The apron:

  • stiffens the top, helping to keep it flat
  • transfers the load to the legs
  • connects the legs to each other and keeps them vertical
  • connects the top to the base (i.e. legs + apron)
  • in a large table, supports stretchers that support the top in the middle
  • provides aesthetic balance for the legs (a 1" top on 3" legs would look funny)

You can ignore the aesthetic function if you choose, but if you want your table to last you have to consider the structural functions. For example, without aprons to support the width of the table, the joints between the boards in the top would experience much more stress than they do in a regular table. Breadboard ends could help here, but they're not a complete solution.

What do you think would happen over time if you screwed legs to the corners of a 3/4" sheet of plywood? Plywood has very good rigidity both lengthwise and crosswise, and there are no joints to worry about. I don't think it'd be long before the top began to sag and the legs started to splay outward. As soon as that happened, there'd be a lot of lateral force on the legs which would cause them to become loose.

Your "spline" idea isn't a bad one, but I think you'll need more than just one down the middle, and it doesn't solve the problem of supporting the top crosswise or bracing the legs.

One possibility is to connect the legs diagonally, forming an X that would support the top. If you want to hide that structure as much as possible you could build it out of square steel tubing, welded at the center, with vertical bits welded on at each corner to support the legs.

On the aesthetic side, now is the time to start making some drawings that will let you really see how your table will look. That'll also force you to think more carefully about the structural aspects of your design.

  • I'm hoping to attach the legs to the top via mortise and tenon, probably at least an inch into the table top. I'm hoping that will function to brace the legs. So you think if I did the spline, I'd need to do more than 1? I kind of assumed that already; I was thinking maybe three total, which would be one about every foot. As to supporting it crosswise, I'm still working on that in my head. I could probably do a brace across and attach with cleats to allow for wood movement. You think that would help stiffen it up even if it's not connected to the legs? – kannon19 Jun 1 '15 at 16:08
  • I think that if you're using 8/4 boards, supporting the table lengthwise is the least of your worries. I used the sagulator to check the sag over a 68" span and came up with 0.02", which seems fine. I'd be more concerned about supporting the width of the table and creating a solid connection for the legs. Remember that the legs are like 28" levers that will be trying to break that 1" m&t joint every time someone leans against the table, slides is across the floor, or hits a leg with a vacuum cleaner. – Caleb Jun 1 '15 at 16:36
  • Also, consider that a 2" top is going to be pretty heavy. At your stated dimensions, you're looking at about 40 board/ft, which comes in around 116 lbs. – Caleb Jun 1 '15 at 16:44
  • yeah, I've been moving it around the shop... It's definitely going to be heavy. I like that, though. – kannon19 Jun 1 '15 at 17:12
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In general, a full 1" hardwood board can span about 4' with minimal bend (supported on the ends for a book shelf with load). So a 2" board should handle the it fairly well. Especially since it is unlikely that the legs are going to be out at the very corners.

But your support can have a big difference in how the table reacts. A single large pedestal will need decent sized 'branches' and 'roots' to support the table, two pedestal's still need a goo solid way to attach and support the table. 4 legs, are going to need something to keep them aligned and help prevent torque on the legs.

I have an old pedestal table I need to fix so I've been thinking about some of these issues. The table itself likely doesn't actually need the apron as such, however, how you plan to support the table on the legs (and attach it) will be where the ultimate decision on what you need to do rests.

  • I bet a 1" hardwood board could span more than 4"! ;-) – Caleb Jun 1 '15 at 12:56
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    @Caleb oops, missed that! changing – bowlturner Jun 1 '15 at 12:59
  • I'm thinking of doing mortise and tenon to attach the legs to the top. I'm thinking at least 1" into the top (maybe even a double mortise and tenon)? Does the double tenon add strength? Sorry for all the questions, and I appreciate the help! – kannon19 Jun 1 '15 at 16:14
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    @kannon19 My gut tells me 1" of mortise and tenon (even a double) is just asking for trouble. You have a 3' lever and to small tenons holding each leg? I think you'd be better off going for 2 pedestals with wide branches. – bowlturner Jun 1 '15 at 16:19
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    @kannon19 you might be able to get away with the apron forming an x under the table and mortising that into the legs. Maybe. – bowlturner Jun 1 '15 at 16:23
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Caleb is very skeptical but I think there's no real reason why you can't do this as long as the table is thick enough.

The fact that you are gluing several boards into one big one doesn't matter - the glue bond should be as strong as the wood itself if done correctly.

And a large span doesn't matter either, as long as the tabletop is thick enough.

The only real issue is how do you attach the table leg to the table top without the connection being too weak (since it will have to carry a fair amount of bending moment). An apron makes this easy because it is essentially a big gusset. One solution I think would be to just use an actual gusset. Like this (although you can probably make it look nicer than this).

table with gussets

Another solution might be to just have really really huge table legs like this:

table without apron

For some reason that table is called the "Apron Dining Table" (??). Anyway for that you'll need to use a load of dowels because you're gluing to end-grain which doesn't really work.

And finally you can use metal, which is what all IKEA desks do:

ikea desk leg connection

I'm sure you can find a posh version of that sort of thing somewhere (or make one if you can weld etc).

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Assuming the table top is stiff enough by itself, concealed steel posts into which the legs socket might work well.

Here is a more involved idea, assuming your using thick, solid legs:

Rip each leg into two halves, route a groove down the center of each, and then glue them back together, creating a 'tube'. Weld a long nut to a plate inset into the top, and then use threaded rod down through the leg with a nut and thick washer to cinch the leg up against the table top.

If the leg is round, you could just use a threaded post and socket to screw it onto the bottom of the table. I don't know how sturdy that would be over time, but...

Just some ideas!

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