How to strengthen a 19mm oak panel

[ol_london]

could you route out slots in the top for something like an l shaped section of metal like this:

so you have the 'thickness of the metal (13mm in this example) and then the bit at a right angle to it has holes in to secure it to the wood?
View attachment 103119

Hi. Thanks. Are you thinking cross ways to reinforce the width or running the length of it? Hard to tell which would work best.

 

[Jacob]

If you don't want to make a conventional table you could make a table with a thick sheet of ply for the top, smaller than your panel, then stick the panel on top of that?
The idea of "strengthening a panel" is a bit of a red herring - it's about "how to make a table".

 

[ol_london]

If you don't want to make a conventional table you could make a table with a thick sheet of ply for the top, smaller than your panel, then stick the panel on top of that?
The idea of "strengthening a panel" is a bit of a red herring - it's about "how to make a table".

Interesting. What do you think the minimum ply thickness that would work to create a stiff surface once joined to a panel? 15mm birch?

 

[Jacob]

Interesting. What do you think the minimum ply thickness that would work to create a stiff surface once joined to a panel? 15mm birch?

15, 18 perhaps. It's only a small table 1500 x 600 so a piece of ply say 1200 x 450 (more overhang at the ends).
Personally I'd just make a table - a 4 legged standalone construction on which to perch a table-top of typical thickness.

 

[ol_london]

15mm birch on hairpins as a base frame, then 19mm solid oak overhanging on top
Sounds like a good plan. Thanks for that.

 

[Jameshow]

Just remember to put the screws in slots as opposed to holes as shown up thread.

So that the timber top has the ability to move otherwise you will end up cracking it when it swells and shrinks according to humidity.

Cheers James

 

[ol_london]

T

Just remember to put the screws in slots as opposed to holes as shown up thread.

So that the timber top has the ability to move otherwise you will end up cracking it when it swells and shrinks according to humidity.

Cheers James

Thanks James. Noted. Does it matter which direction the slots run in?

 

[GarF]

Does it matter which direction the slots run in?

Yes

 

[Jameshow]

Across the grain of the board supported.

Cheers James

 

[Jacob]

Across the grain of the board supported.

Cheers James

And no countersinking - dome screw heads plus a washer so that movement is possible.
It'd be the functional equivalent of the buttons holding a conventional table top.

 

[Jacob]

[

Nope, still wrong.

A box beam is reliant on the edges of the panels being joined together to reinforce the structure.

A torsion box relies on the faces being joined together for its strength.

Faces, not edges.

Nope.
The faces of your "torsion box" are joined by the edges (or it wouldn't be a box) and this is what makes it strong (and resistant to torsion). A box with one side missing is much bendier/twistier.
Adding extra structure inside the box to make it stronger/stiffer doesn't make it radically different in principle - all sealed boxes are "torsion" boxes, so the term "torsion" is a bit redundant, although we know what you mean!

 

[TheTiddles]

[

Nope.
The faces of your "torsion box" are joined by the edges (or it wouldn't be a box) and this is what makes it strong (and resistant to torsion). A box with one side missing is much bendier/twistier.
Adding extra structure inside the box to make it stronger/stiffer doesn't make it radically different in principle - all sealed boxes are "torsion" boxes, so the term "torsion" is a bit redundant, although we know what you mean!

Yawn.
no.

 

[ol_london]

Thanks for explaining, I’ll make the slots run across the grain.
Now I wonder if anyone knows what a torsion box is by any chance?

 

[Jacob]

Thanks for explaining, I’ll make the slots run across the grain.
Now I wonder if anyone knows what a torsion box is by any chance?

Book - "Structures" J.E Gordon probably coined the expression in describing how the wings of a biplane don't twist - thanks to the diagonal bracing which he described as amounting to a sort of cage or 'torsion box' (his words, in inverted commas)
He expands on this (p269) - "Torsion can therefore be resisted by any kind of box or tube whose sides may be continuous or alternatively of open work lattice construction"
Hence all boxes resist torsion if their sides are continuous, whether or not they contain any extra structure or reenforcement.
"Torsion box" isn't a technical definition of different sort of box it's just a loose expression he threw in by way of explanation of the biplane lattice wing construction - as analogous to a box.
It got picked up by the amateur woodwork scene somehow!

 

[TheTiddles]

Thanks for explaining, I’ll make the slots run across the grain.
Now I wonder if anyone knows what a torsion box is by any chance?

Only people who can use google or read books

 

[Jacob]

Only people who can use google or read books

It's a good book for the general reader - not too technical Structures
You don't get much on google - just the woodwork idea, woodwork is where it has taken root!
In fact there is no structure actually inside Gordon's biplane "torsion box" except the plane itself, and a Biggles character!