Ive been asked to build a very large conference table – 24ft long, 4 ft wide. It needs to have a leaf (or two) that can be removed that will result in a 16ft table length. I will be using shop-sawn walnut veneer for top surface, top thickness is 1.5in. My question to this learned group is what should i use for subtop? Ive thought about simply gluing two pieces of 3/4 baltic birch, but will be heavy and not very flat. The other option ive considered is mini tortion box made up of 1/4in baltic birch top and bottom and 1 in plywood ribs. Any thought/ideas/opinions are most welcome.
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I like the torsion box plan. But, I wouldn’t use ply ribs—did that once and had a surprising amount of trouble with them staying flat during assembly. And they’re unnecessarily heavy, as the engineering that makes torsion box so rigid and strong isnt at all about the density/mass of the ribs. I’d use something lighter and stable…basswood, poplar, or clear pine? Also, I’d opt for 1/4” mdf for the top/bottom skins. Smoother, flatter and generally easier to veneer in my opinion.
That’s a big table! Good luck.
thanks for your reply. that's interesting you had trouble with plywood ribs, I would have thought would be more stable/flat than solid wood. also good suggestion re 1/4 " mdf.
you can also buy engineered honey comb (from the makers of UniBond, I believe) that I've successfully used. https://www.vacupress.com/product/resin-impregnated-honeycomb/ Comes in a variety of thicknesses, works well, and is lighter than solid or plywood.
I’ve never used the honey comb stuff…but is it super cool!! That is a great suggestion worth investigating, and Daryl at Vaccupress is a fantastically knowledgeable resource. I’ve seen the stuff used in curved forms…I think they even make in aluminum.
Hollow core doors just use a zig-zag of corrugated cardboard. It only needs strength in one direction.
Hey there - Epic project! Haven't made anything quite that size, but a few things I would be thinking about...
- Two layers of Baltic Birch is going to be ungodly heavy/unwieldy... Lots of cabinet shops around here in NorCal use MDF (or liteweight MDF) for veneered projects, but even heavier... I agree with mattk41 that a torsion box would be the way to go.
- One downside of torsion boxes for tops is they do sound a bit hollow - would definitely mock up one and see. One way around it is to use relatively wide cross members fairly closely spaced. Light materials the way to go. Around here poplar would be my choice. Thinking I would use at least 1" width cross members spaced 4-6" apart, maybe even tighter, all half lapped and glued together. Easy to do it in many glue-ups rather than one massive one. Outside edges of it I would use 2-3" wide poplar.
- Hard to get very large torsion boxes completely flat, so might consider gluing up your interior and then having it run through a wide belt sander if it is an option - our local lumber place has a 54" wide belt sander.
-Als0 agree with use of 1/4" MDF skins. Takes veneer well and won't show through thin veneers.
- I would definitely do a balance veneer on the bottom otherwise even a torsion box may turn into a taco!
- How to do the glue up? Presumably using a huge veneer press - will need a daily slow setting glue to make sure you have enough working time.
- Use wide (2-3"?) walnut on outs edges.
- Going to be challenging figuring out how to lay out a pattern for the walnut to look good across 24 feet!
Please let us know how you end up approaching it and how it turns out - good learning experience for everyone!
My first thought on a 24' table is,--- is anyone worried about the weight?
If I was presented with the problem -- build me a 24' table that can convert to a 16' table ---I would hope there was a large budget attached. My mind would think solid wood for the top and I know where such a thing might exist and I'd hope I can get out of there for under $25,000. Logistically id probably have to rent a crane or gantry or something to handle it on my end.
But be as it may , veneer over a core, I would probably opt for a wood core for my veneered table. I'd make a lamented slab ,possibly poplar. Doing this gets me away from modular thinking in plywood dimensions. Unless there is some other factor that requires that the table is 4 ' wide ,in my minds eye, 4' seems very narrow for a table so long. From a design point you dont want supporting members ( legs) interfering with people sitting. On another more practical point a conference table should be wide enough so someone cant throw a punch across the table! A torsion box wouldn't ,I would think, give the feel of a solid ,substantial thing. A conference table should feel like that, like it means business! I mean in that case you could make the thing out of hollow core doors. I'd bet you could actually order 4' wide by 8 ' doors like that. You know ,for the budget minded fortune 500 board.
I have a way that I have made a folding drop leaf, actually stole the design from some Dane, that drops below the table and lives there , but would it work on a table so large? I could spend a week trying to figure that out. Could the " leaf(s) " actually be on the ends -and if how? Bad things happen to table leaves that get carried away and stored. They get abused and from what I've experienced from my restorative work ,eventually lost! Thats not your problem however. Having the two ends separate and leaving a 8 foot gap to install the leaf(s) is going to be tricky engineering and is going to require some kind of support. How many sets of legs on a 24' table?
Anyway, it seems like a really interesting project. Id like to see how you solve this. Not just the top but the whole thing. Hope you have a big room!
Echoing many others, torsion box is definitely the way I would go, having built 16' conference tables both solid (10/4 ash, full 16' lengths.. a very physically taxing build early in my one man shop career...) and torsion box style. I have not found the issues mentioned above with plywood ribs but you'll need a good and dead flat assembly table to build the cores from plywood for sure. Clear pine would be my solid wood choice. 1/4" MDF skins, solid nosing and then veneers laid up and pressed.
My only hard won advice would be have very detailed drawings of all your connection points on the bottom for leaf hardware, base attachment, etc., and let in blocking of some kind to make sure you don't need to hit your core grid and can attach anywhere you'd like in the general area it will align.
Have fun - sounds like a fun project!
I think we are ready to ask for a few questions about the design to further comment the top construction, mainly about the base and extension scheme. Being a conference table, I have to assume a pedestal or trestle base. Going from 16 to 24 feet’s will require 8 foot of extension, then again I assume 4 ft extensions on both ends, which a light torsion box design would not be able to support so extension rails would extend from the top of the base ? See where I am going, so please indicate more details of your intended design if there are some, for me discussing the top build is only meaningful with the design of the supporting structure.
a lot of really great info here already, thanks very much for giving time and thought to this problem. I will def looking into the honeycomb stuff.
re other design parameters, still tbd, and I think largely up to me. see picture below of table in shop at the moment that I made several years ago, (refinishing now) - this is the table that started the discussion, customer said 'can you make a version of that at 16-24ft?'. so I was thinking 2 very large bases, each supporting a 8ft section, then middle expands to accept 2 - 4 ft leaves. would have to make the extension mechanisms myself (huge telescoping/sliding dovetail thing), and even then might need to have a center leg attached to one of the leafs to help with supporting huge cantilevered weight.
really good comment about torsion box sounding hollow, I thought about that as well, last thing a $40-50k table would want to be is hollow sounding :). pls keep thoughts and questions coming, really helping my thought processes.
What you said about a center leg to support the leaves implies that the bases will spread as the table expands. This seems unrealistic for an office scenario. A table that requires two weightlifters to open in a probably-carpeted room will never be opened. Plus, most big-time board rooms nowadays have floor-feed tech built in for video calls etc. A 50k table says big-time.
Think about a steel under-top structure with roller bearings, center section and base fixed, both ends expanding out to take a mid-leaf each. Sized right you might work leaf storage into the central base setup.
The largest table I have made to date is a 4' by 8' conference table out of reclaimed elm (from a 1860's dairy farm barn) which was about 3/4" thick after milling. I have attached photos of the underneath of the table showing the grid (poplar) which maintained the dead flat structure of the table and also shows how I wrapped the edges to have the appearance of a thicker table (about 1.5"). The trestle base was made of the elm and reclaimed oak laminated to gain the appropriate thickness for the structure. This table was made 5 years ago and the buyer tells me it is still flat and stable. The table felt and sounded solid when the build was finished.
There is a good article "Thick Table Tops From Thin Stock" on the Fine woodworking site. Just search thick tabletop. If I were paying 40 to 50k for a conference table I would really not want a veneered top. I would expect solid wood.
Don't have many ideas about the leaf to expand the table except the observation than a 4/4 leaf with wrapped edges will be much lighter than the other possibilities suggested. Good Luck and please post the results.
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I would think for a table that size you would want the extra weight to prevent bumping an open gap between them. My suggestion would be to use a full thickness of MDF for the top layer with plywood underneath at your base attachment points and that surrounded with more MDF pieces to fill out the dimensions. And use the torsion box construction for the leaves.
As for moving that weight, maybe use the levelling screw in feet tucked in where they can't be seen, with those sitting in those saucer shaped carpet glides. From experience, I know they allow one or two people to move a lot of weight without struggling.