slab table base design

[Prashun Patel]

I'm making a dining table like this one:

http://www.bddw.com/furniture/table/slab_tabl4.html

The client wants a steel base like this, but how in the world can un-stretchered legs like this resist racking?

Is this safe?

[Mark Bolton]

If the mounting surface at the top is substantial enough I wouldnt have a problem with it. There are of course all kinds of issues with bronze and potential for cracking and so on but it looks like the mounting at the top is fairly large and as a general rule anyone who would pay for such a table would likely treat it like a table as opposed to a ladder, or work bench.

How do you plan on fabricating those legs out of steel?

[Michael Mahan]

I'm making a dining table like this one:

http://www.bddw.com/furniture/table/slab_tabl4.html

The client wants a steel base like this, but how in the world can un-stretchered legs like this resist racking?

Is this safe?

the large surface area at the top of the twin bases that mount to the table top prevent that from racking
that's cast as a whole unit on each support so doing that in steel is not gonna be easy , know any good iron workers ?

[Sam Murdoch]

I can't see the mounting pads in any of the photos. Your question is a good one. Hard to know how a table will get used and your concern is warranted.

This could work (I think) with a couple of considerations: 1) that the table top is thick 1-3/4" or more 2) The pads on top of the base sections are at least 3" and preferably 4" to 6" wide x 1/2 of the table width x 3/8" to 1/2" thick. 3) the pads could be set into the underside of the top flush and fitted tight side to side. The ends would be open to allow for the expansion of the top but in the long dimension of the top there could be no movement. With a heavy top I think you could secure the pads at the center with a through bolt into a t-nut or other insert set into the table top. That center fastening could be tight. On either side out to the ends you could run screws into the top through elongated holes in the metal plate.

I really like the table photos that you linked to. That bronze base is pretty if questionably practical.

[Jamie Buxton]

I had an inquiry about a table with those cast bronze legs. I couldn't find a source for them. I suggested welding up a simpler version from steel, but she really wanted the curve and taper, and my welder friend was getting pretty nervous. Eventually she did something else, and I was relieved. At any rate, if you figure out a source for the legs, or figure out a simpler steel version, I'd like to hear about it.

[Prashun Patel]

I am not sure what the thickness of the table has to do with it. Wont i be relying on some bolts to prevent the several hundred pound top from racking the skinny legs? There is nothing in the long direction of the table to prevent it. I mean, its basically a trestle table with no trestle. The stretcher needs to be in between the legs.

[Jamie Buxton]

I am not sure what the thickness of the table has to do with it. Wont i be relying on some bolts to prevent the several hundred pound top from racking the skinny legs? There is nothing in the long direction of the table to prevent it. I mean, its basically a trestle table with no trestle. The stretcher needs to be in between the legs.

The stretcher on a trestle table does provide some anti-wrack strength, but not much. Look at the thing from the side. You see a big open rectangle. It can wrack into a parallelogram. If you really want anti-wracking, put some diagonal element in that rectangle. That will really stiffen up the structure.
For instance, weld an 8"x8" triangle to your steel trestle, with the triangle in the plane that includes the two uprights. The top of the triangle fits up against the underside of the wood top, and is lagged to the wood. That triangle will do a lot more for anti-wracking than a horizontal stretcher.

[Sam Murdoch]

With no stretcher and no diagonal elements (as I see in the photos that you linked to) the only thing I can see adding minimal anti racking to this design is recessing the top of each leg into the table top. The thicker the top the more thickness you can incorporate to the leg top pads. The thick sides of the pads fitted tightly within a recess in the table top along with being securely fastened are the only anti racking you can achieve with this design. I described above how I would secure the top to the legs. The bolt and or screws won't add much to resist racking if you intend to allow the top some movement, which you must.

As we all know - adding a lower stretchers or some diagonal bracing and perhaps even a full bar connecting the two legs at the very top are all huge improvements though the first 2 options are the best. Those aren't shown in the design you are asking about as far as I can tell so I suggest making the top thick and adding some real surface to the pads at the top of the legs. I know you know that is still a compromise but ...

[Prashun Patel]

This is great information. Thanks, guys. I have to make a scale prototype of this to convince myself.

I recently made a shaker trestle table from chris schwarz's plans in popww. The stretcher in that case is tall enough that it certainly does a good job in preventing racking (deforming into a parallelogram) and leg splay (deforming into a trapezoid). I guess that is my real concern here; the top would have to be extremely thick and the leg tops embedded deeply therein in order to prevent leg splay. A deep strether, or low stretcher, or some kind of outriggers on the legs are the only ways i see to resist splay.

[Ethan Melad]

it looks to me like there is good sized round mounting plate at the top of the legs - if you designed the legs with even larger plates that could help avoid racking, couldn't it? in addition, letting the mounting plate/flange into the top would add some strength... i think adding any visible stretcher or diagonal would completely alter the aesthetic of the table.

[Jamie Buxton]

Here are two pics of a set of steel table legs I built 30 years ago. The flange on the top is 10" square and 1/2" thick, screwed up to the table top with #14 screws. The leg is 1 1/2" square cold rolled steel. The table top is solid cherry, about 1 7/8" thick. The table is very solid; it does not wiggle at all if you whack it with a hip or something.

steelleg.jpgsteellegtop.jpg

[Kent A Bathurst]

it looks to me like there is good sized round mounting plate at the top of the legs - if you designed the legs with even larger plates that could help avoid racking, couldn't it? in addition, letting the mounting plate/flange into the top would add some strength... i think adding any visible stretcher or diagonal would completely alter the aesthetic of the table.

Agreed - there is a round plate at the top of the legs, and stretchers would give you a completely different aesthetic.

Jamie's photo shows what the game looks like.

[Prashun Patel]

Exactly the answers i was hoping for. Thanks you guys. Jamie, you just cant beat 30 yrs empirical evidence. Thank you.

[Michael Mahan]

I was a professional commercial mover for many years all the 18' to 24 foot boardroom tables I've ever moved all had a large surface area plate at the top on the leg assembly , the larger the table , the larger the suface area of the upper plate . Those do not rack , these table tops were composite &/or MDF tops with veneer & were much heavier than these slab tops . I remember one 24' top very well it went 20 stories down the fire escape stairs as It wouldn't fit in the freight elevator . it was a custom job that didn't have a joined 2 piece top as when 1st placed in the room it was assembled & laminated in the room so not to have a line in the middle . Our company was know to take out windows & hire a crane to move other large items in/out .