Thread: Brains trust: Torsion box shelves

I built a torsion box 3.6 metres long as a work bench that is quite heavily loaded. The whole ethos of TB's is light and strong so the top and bottom were 6mm MDF and the core framing 3mm MDF. Two people could lift it easily and it is well loaded with multiple sewing machines. I arrived at 3.6 metres because I could buy the sheets at that length and got the supplier to cut them to 600mm wide. I am sure I posted some phots at the time but god only nows where and I am not sure there were any on the internals which were fully glued to the top and bottom sheets.

Originally Posted by Bernmc

I'm going to put up a high shelf for storage in the shed

The shelf will be 600mm wide, and 4.2m long, so it's a biggie.

I'm confident in the shelf brackets - combo of ply sandwich and 90x40 beams
Studs are 450mm

I thought I'd do a torsion box for the shelf. Possibly 20mmx12mm ply for the ribs. Does the brains trust think that skinning it with 6mm MDF would be strong enough, or should I go thicker? I'll end up with a 32mm thick shelf.

your torsion box shelf will be supported with brackets every 450 mm == the stud spacing

Sagulator suggests that
1. you could skin the box with 3 mm MDF
2. you could make the "ribs" from 19 mm high x 9 mm thick ply -- to give a total "shelf" thickness of 25 mm. The ribs could be spaced at the half point across the shelf (i.e. front and read face, plus the centre), and at every stud and the half points (i.e. every 225 mm along the shelf)
3. AND you still park the proverbial truck on your "shelf"

AND, the biggie, your redesigned shelf would be around half the weight (2 x 3 mm MDF, and 9 rather than 12 mm ply) of what you are thinking of building.


Just make sure that the joints are staggered, or located coincident with a stud and support bracket

The one I built has no intermediate support at all and has not sagged over quite a few years or use.

Originally Posted by ian

your torsion box shelf will be supported with brackets every 450 mm == the stud spacing

Sagulator suggests that
1. you could skin the box with 3 mm MDF
2. you could make the "ribs" from 19 mm high x 9 mm thick ply -- to give a total "shelf" thickness of 25 mm. The ribs could be spaced at the half point across the shelf (i.e. front and read face, plus the centre), and at every stud and the half points (i.e. every 225 mm along the shelf)
3. AND you still park the proverbial truck on your "shelf"

AND, the biggie, your redesigned shelf would be around half the weight (2 x 3 mm MDF, and 9 rather than 12 mm ply) of what you are thinking of building.


Just make sure that the joints are staggered, or located coincident with a stud and support bracket

thought some more about your proposed torsion box shelf

skins -- 3 mm MDF

ribs -- 3 longitudinal strips cut from 9 mm thick (5 ply), each strip 19 mm high. Alternatively, rip 9 mm thick quarter sawn strips from a board.
Skip the mid point lateral ribs. Just place one at each stud location.
Make sure that the timber or ply ribs run along the shelf. If using ply, rather than butt jointing or scarfing the internal longitudinal strip, it will be simpler to just overlap the ends by say 200 mm.

Originally Posted by Chris Parks

The one I built has no intermediate support at all and has not sagged over quite a few years or use.

Note that I'm suggesting Bernmc use 3 mm skins -- not the stiffer 6 mm skins used by yourself. At a 600 mm span, 3 mm MDF will sag somewhat, hence the central internal rib.
My suggestion of lateral ribs corresponding with the stud spacing is almost a belt and braces approach. Bernmc could probably get away with lateral stiffeners every 2nd or 3rd stud.

I put in a complete 100mm square grid of 3mm MDF. This is the bench, the drawers under it do not provide support

Sewing Room Bench 5.JPGSewing Room Bench 4.JPGSewing Room Bench 3.JPGSewing Room Bench 2.JPGReturn On Sewing Room Bench.JPG

Chris
are you just showing off the torsion box bench you built for SWMBO collection of sewing machines (BTW, I quite like it) or are we arguing ?

I hope we are not arguing ...


your bench is a "bench" so of course the section needs to be much deeper than Bernmc's "shelf"

my "design" is based on very thin skins -- the shelf will be so high that Bernmc will need to be standing on a tallish ladder to see the surface of his storage shelf. In that context I don't think it matters if the upper 3 mm skin sags a bit between the 3 ribs. The shelf's height will be too great to see the sag, and the underside will remain flat. But if Bernmc wants additional support, he could reduce the rib spacing to 200. Reducing the spacing to 150 mm, would IMO be very much overkill.

the shallow longitudinal ribs I'm suggesting for Bernmc plus the thin skins is where the shelf will get it's strength.

again. being a shelf, Bernmc can afford to space the supports at 450 centers. A wider spacing of support -- every 2nd or 3rd stud -- would require a deeper torsion box be built -- potentially compromising the height of the objects Bernmc places on the shelf.


Bernmc's biggest challenge will likely be finding a surface flat enough to build his 420 cm long shelf.


useful tools for building the shelf will include a chalk line to snap the location (offset to one side) of the longitudinal ribs.
and a pneumatic staple gun to assemble the ribs.

Thanks boys.

I think the ply ribs might be a bit easier to deal with for the 'quick-and-dirty' glue and nail build. I'll give it a bit of thought. But not much!

Gives me an excuse to upgrade my nailer - I have an old cheap electric thing that always leaves the nail head exposed.

Not knowing too much about the beasties, any suggestions on a suitable pneumatic nailer?

Options seem to be cheap - Ryobi Airwave 3 In 1 Air Brad Nailer And Stapler | Bunnings Warehouse (I'm not a fan of buying cheap and then buying again, and I'm unsure of the modern ryobi build)

vs Something like this DeWalt - DeWalt 12-65mm C Series 16ga Precision Point Air Nailer Bradder DPN1664PPXJ | Total Tools

Bunnings do the bostich range, who I think make some of the DeWalt stuff too?

Application would be mostly nailing ply and mdf panels at this stage

Hi Mr B. One thing to be wary of with combo nailer/staplers is that they use a wide firing pin. Fine for staples but leaves a big depression when nailing. I have a Hitachi bradder that uses C1 nails. Thes are slightly thicker than C series nails and less likely to bend in harder material and snap if you try to remove them

Sydney Tools

Also: any experience with the cordless nailers - Home - Products - Powertools - Fastening Tools & Nailers - Nailers - XR Battery Cordless Nailers - Agrafeuse 18Ga XR 18V 2Ah Li-Ion BLAgrafeuse 18Ga XR 18V 2Ah Li-Ion BL - DEWALT

I already have a few XR battery tools, so in the system already. Quite bulky by the looks of it though - around 3kg with the battery I expect. But it might be a worthwhile payoff not to have to drag the air hose around.

This is my third attempt at drafting this reply ...

Originally Posted by Bernmc

I think the ply ribs might be a bit easier to deal with for the 'quick-and-dirty' glue and nail build. I'll give it a bit of thought. But not much!

Gives me an excuse to upgrade my nailer - I have an old cheap electric thing that always leaves the nail head exposed.

a pneumatic stapler will make the shelf building task easier, but the expense is not warranted if along with the gun you also have to purchase a compressor, air hose, reel, etc

Your existing electric nailer "that always leaves the head exposed" can be used to toe nail the ribs together. After all is said and done the applied skins will cover everything up.

To attach the skins, use wax paper to protect the surface you're working on, plenty of glue, and your electric nailer to tack the skins down while the glue sets up. Before [carefully] turning the shelf over to skin the other side, use a hammer to seat those nails which have exposed heads.


Personally I'd use 140 mm x 4.8 m long pine lining boards Tru Choice 140 x 12mm x 4.8m Shiplap Pine Lining | Bunnings Warehouse for the ribs. Just rip 19 or 20 mm strips off the board. I haven't calculated how many strips you will need, but suspect that after ripping off the tongue, a single $14 board will yield all the stock you need and then some.

For 'quick and dirty', pine lining boards will be impossible to beat.

Originally Posted by Bernmc

Not knowing too much about the [air powered] beasties, any suggestions on a suitable pneumatic nailer?

Options seem to be cheap - Ryobi Airwave 3 In 1 Air Brad Nailer And Stapler | Bunnings Warehouse (I'm not a fan of buying cheap and then buying again, and I'm unsure of the modern ryobi build)

vs Something like this DeWalt - DeWalt 12-65mm C Series 16ga Precision Point Air Nailer Bradder DPN1664PPXJ | Total Tools

Application would be mostly nailing ply and mdf panels at this stage

Originally Posted by Bernmc

Also: any experience with the cordless nailers - Home - Products - Powertools - Fastening Tools & Nailers - Nailers - XR Battery Cordless Nailers - Agrafeuse 18Ga XR 18V 2Ah Li-Ion BLAgrafeuse 18Ga XR 18V 2Ah Li-Ion BL - DEWALT

Bern

If the primary use for your nailer is nailing ply and MDF panels, just stick with your existing [cheapish ?] electric nailer.
Wait till you get a job where the appearance is important before investing in a new cordless nailer.


I've been eyeing-off one or two options locally [in Calgary] but can't get past the CAD $379 sticker shock for a 23 ga cordless pinner.
Then there'd be a cordless 18 ga bradder, a cordless crown stapler, plus a cordless glue gun for the "kid". Far, far too expensive at this stage.

I've got a compressor or two lying around, along with hosing, so it wouldn't be too expensive to add a pneumatic nailer. The little electric one is so bad that I don't like using it, and often end up glueing and screwing, or even domino-ing and clamping instead. So it's pretty bad! But maybe I will give it another try with this low rent job... or just pick up that $160 HiKoki C1 gun.

The pine boards are also a very good find.

I do enjoy how these simple projects generate excellent and informative discussion - such a good forum.

If you already have a compressor go for a pneumatic stapler.
Forgive me for not recommending a particular brand, just remember it would be good if what you end up buying takes standard 1/2" or 5/8" staples.
Given that the staples are only to hold the cross ribs to the longitudinal pieces, you won't want a staple much longer than 10 mm or thereabouts.
For upholstery work you might want a staple up to 15 mm long.


And while you're at it, get yourself a 23 ga pinner to tack the MDF skins on with. On the rule of 1/3rds the headless pins would want to be in the order of 15 mm long