What species would be on your shortlist for a slab desk?

[sawdustandwax]

54mm would be a good thickness, if using pre veneered mdf have it cut lengthways into two equal widths. The front, already finished in veneer could sandwich another 18mm piece of contrasting soild wood, that could set back a few mil, or reeded or rounded or laser engraved with a favourite quote or whatever your taste. That would use 50mm no4 screws, pilot drilled with whole thing c-clamped together whilst putting the screws in, best to finish by hand or torque-limit the driver. Alternative is a solid piece on the front, glued on and carefully card scraped level.

 

[TheTiddles]

Veneer could give you fabulous grain, you might run out of budget again though.

If it was me I would too veneer a box about 100mm deep or a laminated section of 3x18mm with an apron or support of some nature.

 

[Sideways]

I'm with Jacob. I'd use steel to support the long front edge. Proper steel, not some feeble piece of angle from B&Q. Steel reinforcement will be thinner than a torsion box of the same strength.

 

[D_W]

resaw hardwood (bookmatch it for interest) and glue it to a baltic birch ply box/frame.

By resaw, I mean leave yourself a surface on the order of 1/8th to 3/16th thick. I haven't used ply for something like that in a long time, but I have a flatsawn case top in the upstairs of my house that's about half that size in every direction and the top is nothing but cherry glued with copious amounts of glue to baltic birch 3/4" ply.

The guy who got me into woodworking was obsessed with the idea that nothing but trim should be "real" wood through and through.

(that case top is nearing 20 years old now).

 

[el_Pedr0]

Nice - this is turning out to be a font of inspiration.

54mm would be a good thickness, if using pre veneered mdf have it cut lengthways into two equal widths. The front, already finished in veneer could sandwich another 18mm piece of contrasting soild wood, that could set back a few mil, or reeded or rounded or laser engraved with a favourite quote or whatever your taste.

@sawdustandwax - in the above, would I still create a torsion box framework inside the void? I.e. a framework of 18mm-high members arranged between the top and bottom faces and all hidden behind the solid wood filler? Or are you suggesting just a third piece of non-veneered mdf so that it's in essence a 54mm laminate slab of mdf? And in the latter - presumably I'd still need an apron or steel for support.

 

[Jacob]

I'm with Jacob. I'd use steel to support the long front edge. Proper steel, not some feeble piece of angle from B&Q. Steel reinforcement will be thinner than a torsion box of the same strength.

Except mine's wood - 50 x 90 mm rail set in a bit behind the edge. So with the 18mm mdf thickness I lose 108mm. Still room to get my knees under it! You need about 600mm to clear your knees on an average height chair.

Here it is sorry about the untidyness, 2900 wall to wall, x 930 x 18mm

The rail is housed in the legs against the wall (bits of old joist hence the cut outs).
The hardwood lipping isn't structural and is attached to a batten behind instead of straight on to the 18mm mdf

 

[Jameshow]

Torsion box would undoubtedly be strong, but also presumably thick. What overall minimim thickness do you think I could get away with in a torsion box assembly?

2"

12/ 25 /12?

Perhaps even 9 / 25 /9

Cheers James

 

[Jacob]

"Torsion boxes" are a bit of a myth. All boxes are torsion boxes (in the intended meaning). Other non-box structures resist torsion. A table top is not subject to torsion to it's irrelevant anyway. A plywood box would be good if you wanted to veneer it but torsion has nothing to do with it.
2" solid or laminated most timbers would do your 2.4m span no prob.
A cheap option would be a fire door which are available 2.4m and 45mm thick.
A trad way of supporting a massive table top is to rest it over two trestles. Makes it much easier to move. Fitting it to a space seems a bit pointless, why not just have it as a large mobile table on trestles.

 

[el_Pedr0]

Fitting it to a space seems a bit pointless, why not just have it as a large mobile table on trestles.

There's two of us working side by side at this desk. In our current set up (which has legs and doesn't quite span the full width), the legs get in the way of our chairs, limit our options with pedastals/draws, and stuff often falls off the edge of the desk. The desk in your picture doesn't suffer from the problems my current set up has.

The priorities for this project are aesthetics and practicality in joint first place, cost being secondary. That's not to say that I can just splurge the cash, but it is important to end up with something that is a bit of a statement. I might sound like I'm obsessing about a desk - but this home office is an important part of a much bigger house rennovation with quite demanding specs.

Currently tending towards steel as the bearer in the hope that its smaller size (vs timber apron) might allow me to mostly hide it from view. And definitely interested in the veneer approach because it eliminates the pot-luck risk of the solid slab which could leave me waiting an unknown length of time for the right slab.

 

[Jacob]

...... I might sound like I'm obsessing about a desk -

No not at all it's all part of the design process!

but this home office is an important part of a much bigger house rennovation with quite demanding specs.

Currently tending towards steel as the bearer in the hope that its smaller size (vs timber apron) might allow me to mostly hide it from view. And definitely interested in the veneer approach because it eliminates the pot-luck risk of the solid slab which could leave me waiting an unknown length of time for the right slab.

You could set a bearer such as mine a bit further back and more out of sight.
If you go for veneer you might also consider other materials. I'm keen on Formica, particularly plain primary colours Post a photo of the last thing you made

 

[sawdustandwax]

"torsion box" is a myth, a YTube creation attention grabber, however it's still a valid method of construction whatever it's called. The framework would be a grid inside the outer layers. With a bit thought a 2.4 mtr length of decent angle iron (which is a good suggestion) 50 or 60mm x 3 or 4mm could be hidden between the layers and unseen, so the overall thickness would be at most 3 inch, removes the need for an apron as such. It would need to sit on bearers, but the design could change so that this torsion ran between the space and then down the walls with just a bear at the back edge, more cost but if you're going to be using for hours and can afford to do so, why not?

 

[sawdustandwax]

maybe that should be 'bearer' at the back edge, unless u know of some friendly grizzlies with time on their paws

 

[TheTiddles]

"torsion box" is a myth, a YTube creation attention grabber, however it's still a valid method of construction whatever it's called. The framework would be a grid inside the outer layers. With a bit thought a 2.4 mtr length of decent angle iron (which is a good suggestion) 50 or 60mm x 3 or 4mm could be hidden between the layers and unseen, so the overall thickness would be at most 3 inch, removes the need for an apron as such. It would need to sit on bearers, but the design could change so that this torsion ran between the space and then down the walls with just a bear at the back edge, more cost but if you're going to be using for hours and can afford to do so, why not?

I’m guessing Jacobs on his usual rant… he’s had it explained a few times over the last decade or so, he’s not getting it.

stiffness of the torsion box is the square of the distance between the faces, so deeper is “better”, but worse for clearance, but compared with an apron it’ll be much less deep for the same stiffness. 2.4m is not a lot and you could chamfer the front face to reduce visual impact, 60-80mm would look right and be stiff enough for a desk. Embedding metal rails would not offer much extra as that’d be another type of design with its second moment of area dwarfed by the torsion box’s one

 

[Jacob]

......

stiffness of the torsion box is the square of the distance between the faces, ......

Not that simple
https://mechanicalc.com/reference/strength-of-materials#stiffness-multiple-load-pathshttps://mechcontent.com/torsional-s...ffness is defined as,Torsional stiffness = TθMy point is that the word "torsion" is irrelevant in considering a box as a structure, unless it's being designed to resist torsion, which in this case (and most amateur woodwork chats) it is not.
Just being pedantic, but yes a box construction can make a strong structure with less material than a solid structure of the same overall size, but not necessarily a "stronger" one. It will weigh less - which is usually the idea.

 

[jetsetwilly]

Back to aesthetics, I think sycamore or ash would look great with that colour scheme, esp if you could get some silvery-greeny sycamore grain, and you might be able to get a slab of it for your budget. I wouldn't go too thick without thinking about ergonomics - I hate thick desktops because I like my keyboard fairly close to my lap, so I would rather compromise on eg a central leg than a deep apron. For a two-person desk, a slender (metal?) leg set well back would be v inconspicuous, and you could mate it to some inset C-channel to further stabilise the slab.