Torsion Box table & extension slides?

[cputnam]

I'm considering a tabletop built as a torsion box - about 2 - 2.5" thick. My wife wants a new dining table that can seat 12 but needs it to be 8' long in normal use. She also wants the table (at least the top) to be walnut but is choking on the price for solid lumber, hence the torsion box approach. A 4 x 8 sheet of 3/4" walnut veneer can be had for <= $ 125. One stick of nominal 4/4 solid for edging. What am I missing as downsides in this approach?

[rwe2156]

2 sheets of ply laminated together you have a very beefy, stable top. 

You need to veneer both sides.

Needs support. Apron w/ apron x members.

[jteneyck]

If you use a torsion box you can make the structure underneath and base pretty much any way you want.  If you don't you will have to carefully consider both.  No right or wrong way, but the no torsion box approach has more to consider to be successful - i.e. no sag.  

John

[handi]

I'm considering a tabletop built as a torsion box - about 2 - 2.5" thick.  My wife wants a new dining table that can seat 12 but needs it to be 8' long in normal use.  She also wants the table (at least the top) to be walnut but is choking on the price for solid lumber, hence the torsion box approach.  A 4 x 8 sheet of 3/4" walnut veneer can be had for <= $ 125.  One stick of nominal 4/4 solid for edging.  What am I missing as downsides in this approach?

Why not do a 3/4 ply top with 2” drop edges? All the look with less weight.

As for slides, I built the slides for my dining table as part of the apron. Worked slick.

[cputnam]

Do you guys think that 1/4" top and bottom would work? Would make a seriously light table top. The walnut veneer thickness is the same as for 3/4"

[handi]

Do you guys think that 1/4" top and bottom would work?  Would make a seriously light table top.  The walnut veneer thickness is the same as for 3/4"

Structurally, it would work ok, but it would sound hollow and any sharp impact could punch through. The bottom skin would be protected, but the top should be at least 1/2” IMO.

[jteneyck]

Do you guys think that 1/4" top and bottom would work?  Would make a seriously light table top.  The walnut veneer thickness is the same as for 3/4"

What Handi said.  And keep in mind that plywood has a relatively high thickness variation which you will likely see on a big table top.  You can reduce it somewhat by buying tight specs. plywood (special order and expensive).  But the better option is to use MDF.  It's as flat as possible in a wood product and you can specify the veneer cut you want.  

John

[Mike in kc]

Simply offering "concept" information here.   I've built several tables, using using this same structure, a pair of 3/4" ply laminated sheets for the tops, and the end leg assemblies with a single stretcher down the middle.  They've held up very well for some ten plus years under some extreme loads, and they've shown no sign of sagging.

This is  well over a ton of weight.


Here is the support structure, and of course for a dining table the structure would be much much lighter, and the stretcher at least 4 feet shorter and not nearly as wide.   This thing was built for a constant 1+ ton load.  An inch and a half of good ply  will definitely fill the bill for your table top.   I doubt the table would be moved often, so I wouldn't be too concerned about weight.   Of course Veneer and couple inches of solid edging would be needed, but this approach is much faster and easier than a torsion box.  



Although I didn't build this one, this 6 foot table was built around 1980 using the same basic construction, and veneered with teak.   Its been in constant use ever since, first as a dinning room table then for the last few years, as a computer table,  and as you can see by the reflections, its still flat.

[cputnam]

Thanks again Gentlemen!

Hadn't thought about the sonic qualities and lack of impact resistance in 1/4" ply and had completely forgotten about thickness variation of ply in general.

I really like the idea of veneered MDF. We need to keep this table as light as possible. Although my wife is a mighty-mite, she petite at a claimed 5' 2". That plus I've got a peg leg that I'm just learning how to use. Our combined ability to lift dead weights is quite low.