I'm building a suspended shelf which will hold a hefty (14kg) video
projector. There's a picture of a previous, less substantial, version
at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg

Fixing it securely to the ceiling joists will be no problem but I wonder
about the shelf itself: a sheet of, say, 18mm MDF or similar will add
substantially to the weight of the whole thing. I've seen doors - and
indeed, shelves - made like a sandwich, with two thin outer layers and a
honeycomb lattice of some light material (cardboard?) between, which
seems to give a very strong construction, not prone to flexing.

I'm not likely to find something of the right size ready-made, so is
such a thing DIY-able? I have a suspicion that machine tooling and
perhaps assembly under considerable pressure, would be required. But
perhaps I'm wrong.

Alternatively, any other suggestions for a suitable approach will be
welcome. Thanks.

Bert

On 24/09/2023 09:00, Bert Coules wrote:
> I'm building a suspended shelf which will hold a hefty (14kg) video
> projector.  There's a picture of a previous, less substantial, version
> at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg
>
> Fixing it securely to the ceiling joists will be no problem but I wonder
> about the shelf itself: a sheet of, say, 18mm MDF or similar will add
> substantially to the weight of the whole thing.  I've seen doors - and
> indeed, shelves - made like a sandwich, with two thin outer layers and a
> honeycomb lattice of some light material (cardboard?) between, which
> seems to give a very strong construction, not prone to flexing.
>
> I'm not likely to find something of the right size ready-made, so is
> such a thing DIY-able?  I have a suspicion that machine tooling and
> perhaps assembly under considerable pressure, would be required. But
> perhaps I'm wrong.
>
> Alternatively, any other suggestions for a suitable approach will be
> welcome.  Thanks.

The ikea tables @ £12 are made this way (honeycomb cardboard inner) -
your picture shows an upside down table

https://www.ikea.com/gb/en/p/lack-side-table-oak-effect-60111340/

or larger
https://www.ikea.com/gb/en/p/lack-coffee-table-white-90449905/

--
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On 24/09/2023 09:19, alan_m wrote:

> The ikea tables @ £12 are made this way...

Thanks very much for that, Alan. Annoyingly - but pretty much
inevitably - the top of the small version is just a tad too small and
the large one much too big. I could extend the width of the small one
by fixing timber (or whatever) additions to the sides, though they would
probably be tricky to blend in seamlessly. Do you think that the
alternative - cutting down the large one - would severely compromise its
strength?

Bert

Ha! It's just occurred to me that if by good chance the legs are the
same width as the depth of the top they could be ideal for increasing
the width.

On 24/09/2023 09:19, alan_m wrote:
> On 24/09/2023 09:00, Bert Coules wrote:
>> I'm building a suspended shelf which will hold a hefty (14kg) video
>> projector.  There's a picture of a previous, less substantial, version
>> at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg
>>
>> Fixing it securely to the ceiling joists will be no problem but I
>> wonder about the shelf itself: a sheet of, say, 18mm MDF or similar
>> will add substantially to the weight of the whole thing.  I've seen
>> doors - and indeed, shelves - made like a sandwich, with two thin
>> outer layers and a honeycomb lattice of some light material
>> (cardboard?) between, which seems to give a very strong construction,
>> not prone to flexing.
>>
>> I'm not likely to find something of the right size ready-made, so is
>> such a thing DIY-able?  I have a suspicion that machine tooling and
>> perhaps assembly under considerable pressure, would be required. But
>> perhaps I'm wrong.
>>
>> Alternatively, any other suggestions for a suitable approach will be
>> welcome.  Thanks.
>
>
> The ikea tables @ £12 are made this way (honeycomb cardboard inner) -
> your picture shows an upside down table
>
> https://www.ikea.com/gb/en/p/lack-side-table-oak-effect-60111340/
>
> or larger
> https://www.ikea.com/gb/en/p/lack-coffee-table-white-90449905/
>
>

I replaced a UPVC door panel recently. Two sheets of thin UPV on the
outside, inner was 4mm mdf and foam. I'm not sure that there would be
much weight saving but the wholw cobstruction appears to be stiff.

Example
https://www.dnkservices.co.uk/24mm-white-flat-panel

Also in 28mm thickness (which is what I used)

--
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On 24/09/2023 09:43, alan_m wrote:

> I'm not sure that there would be > much weight saving...

I think you're right. I do like the Ikea table notion, but on
reflection, extending it would probably not be a good idea: since the
uprights holding the shelf need to be close to the edges, I have a
vision of the centre part, complete with £7000 worth of projector,
plummeting floorwards while the extended sides remain firmly attached to
the ceiling.

On 24/09/2023 10:50, Bert Coules wrote:
> On 24/09/2023 09:43, alan_m wrote:
>
>> I'm not sure that there would be  > much weight saving...
>
> I think you're right.  I do like the Ikea table notion, but on
> reflection, extending it would probably not be a good idea: since the
> uprights holding the shelf need to be close to the edges, I have a
> vision of the centre part, complete with £7000 worth of projector,
> plummeting floorwards while the extended sides remain firmly attached to
> the ceiling.

I was going to ask whether the projector is valuable ...

I suspect that, even if insured against accidental damage, the insurers
would be reluctant to pay out.

Can you use the rigidity of the projector's casing to help?

Oh, and what's wrong with the one in the photo?

On 24/09/2023 11:05, GB wrote:

> I suspect that, even if insured against accidental damage, the insurers > would be reluctant to pay out.

I'm inclined to agree.

> Can you use the rigidity of the projector's casing to help?

I don't think this is exactly what you mean, but there are ceiling
mounts which use a central column attached to a flat plate which bolts
to the projector's underside. I think they're very inelegant and,
fairly or not, they don't fill me with very much confidence. An example:
https://m.indiamart.com/proddetail/ceiling-mount-projector-15091367473.html

> Oh, and what's wrong with the one in the photo?

The projector in the photo is considerably smaller and lighter than my
new one, and that 15mm shelf strikes me as just a touch too thin. Also,
I can't now remember how I fixed the threaded rods inside the purely
cosmetic tubing into the shelf so that nothing showed on the underside.

Bert Coules <mail@bertcoules.co.uk> wrote:
> I'm building a suspended shelf which will hold a hefty (14kg) video
> projector. There's a picture of a previous, less substantial, version
> at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg
>
> Fixing it securely to the ceiling joists will be no problem but I wonder
> about the shelf itself: a sheet of, say, 18mm MDF or similar will add
> substantially to the weight of the whole thing. I've seen doors - and
> indeed, shelves - made like a sandwich, with two thin outer layers and a
> honeycomb lattice of some light material (cardboard?) between, which
> seems to give a very strong construction, not prone to flexing.

Without the link on your previous message I was thinking about 'suspended
shelf' being the kind where the wall fixings go inside the shelf. Now we
have the picture I don't see what messing about with composites will get
you, since I don't think weight is a big deal. If you make the shelf strong
enough so a child can hang off it, it'll be fine to handle 'only' a 14kg
projector. For other thing, you don't want it to break in case there's an
unexpected sideways load, like somebody bumping into it.

It sounds like the picture has the right idea: some sturdy steel posts, a
sturdy piece of timber sheet, and the last part is the fixings - I'd bolt
the posts to the sheet so you aren't concerned about screws tearing out.
Then the last thing is the fixings into the ceiling joists - some long
screws will likely be enough for that.

If you're worried about stiffness, eg for alignment reasons, then by all
means line the support with something stiffer like foamboard, but don't rely
on the foam to afford you structural strength - it's vulnerable to screws
tearing out.

If you need more rigidity of the assembly, consider triangular cross braces
to prevent it racking if a sideways force is applied.

Theo

On 24/09/2023 09:31, Bert Coules wrote:
> On 24/09/2023 09:19, alan_m wrote:
>
>> The ikea tables @ £12 are made this way...
>
> Thanks very much for that, Alan.  Annoyingly - but pretty much
> inevitably - the top of the small version is just a tad too small and
> the large one much too big.  I could extend the width of the small one
> by fixing timber (or whatever) additions to the sides, though they would
> probably be tricky to blend in seamlessly.  Do you think that the
> alternative - cutting down the large one - would severely compromise its
> strength?

I have successfully cut down egg box style internal doors in the past.
You just need to cut a well fitting bit of timber to glue back into the
cut edge to restore the strength.

Plain flat face light weight doors are a cheap way of getting a large
board of that type:

https://www.wickes.co.uk/Wickes-Flush-Primed-Paint-Grade-Internal-Door---1981-x-762mm/p/239052

(available in various colours)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 24/09/2023 12:47, Theo wrote:

> Without the link on your previous message I was thinking about 'suspended > shelf' being the kind where the wall fixings go inside the shelf.

But there's no suspension involved with one of those; I've always known
that type as a floating shelf.

> ...I don't think weight is a big deal.

It's an important factor if you're working alone and have to offer the
thing up to the ceiling and secure it without an extra pair of hands.

> For other thing, you don't want it to break in case there's an > unexpected sideways load, like somebody bumping into it.

Happily this will be well above head-bumping height and it's very
unlikely that any other sort of collision will occur.

> It sounds like the picture has the right idea: some sturdy steel posts...

Actually, they're just cosmetic: hollow tubes concealing threaded rods
invisibly fixed (but I don't remember how) into the bottom shelf.

> If you need more rigidity of the assembly, consider triangular cross braces > to prevent it racking if a sideways force is applied.

On that earlier model, ensuring that the rods were immovably fixed at
the bottom, tightening the nuts at the top and making sure that the ends
of the tubes were cut dead square did give the whole thing a pleasing
rigidity.

Another thing I've forgotten is what size threaded rods I used:
presumably, the heftier they are the more rigid the construction will
be, though I could be completely wrong and something like M8 would be fine.

Thanks for your thoughts.

Bert

On 24/09/2023 09:00, Bert Coules wrote:
> I'm building a suspended shelf which will hold a hefty (14kg) video
> projector.  There's a picture of a previous, less substantial, version
> at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg
>
> Fixing it securely to the ceiling joists will be no problem but I wonder
> about the shelf itself: a sheet of, say, 18mm MDF or similar will add
> substantially to the weight of the whole thing.  I've seen doors - and
> indeed, shelves - made like a sandwich, with two thin outer layers and a
> honeycomb lattice of some light material (cardboard?) between, which
> seems to give a very strong construction, not prone to flexing.

> Alternatively, any other suggestions for a suitable approach will be
> welcome.  Thanks.

Two sheets of 6mm ply, glued to either side of some expanded polystyrene
or PIR foam insulating board. The edges inset with a fillet of timber.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 24/09/2023 13:35, John Rumm wrote:

> I have successfully cut down egg box style internal doors in the past. > You just need to cut a well fitting bit of timber to glue back into
the > cut edge to restore the strength.

I've worked out a way to use the larger Ikea table (thanks, alan_m)
which will involve cutting the top to length. I've been wondering if I
could separate the end of the discard piece complete with what appear to
be solid blocks at its corners and inveigle that into the open end of
the piece I'm going to use. Your use of a new piece of timber sounds
rather easier.

If all that fails, thanks for the door idea.

Bert

On 24/09/2023 13:37, John Rumm wrote:

> Two sheets of 6mm ply, glued to either side of some expanded polystyrene > or PIR foam insulating board. The edges inset with a fillet of timber.
That's a lovely idea; thanks, John.

Bert

On 24/09/2023 09:00, Bert Coules wrote:
> I'm building a suspended shelf which will hold a hefty (14kg) video
> projector.  There's a picture of a previous, less substantial, version
> at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg
>
> Fixing it securely to the ceiling joists will be no problem but I wonder
> about the shelf itself: a sheet of, say, 18mm MDF or similar will add
> substantially to the weight of the whole thing.  I've seen doors - and
> indeed, shelves - made like a sandwich, with two thin outer layers and a
> honeycomb lattice of some light material (cardboard?) between, which
> seems to give a very strong construction, not prone to flexing.
>
> I'm not likely to find something of the right size ready-made, so is
> such a thing DIY-able?  I have a suspicion that machine tooling and
> perhaps assembly under considerable pressure, would be required. But
> perhaps I'm wrong.
>
> Alternatively, any other suggestions for a suitable approach will be
> welcome.  Thanks.

or a basic torsion box design - a cut 1/2" ply or softwood timber slats
to the required length (say 4 - two for the sides, and two internal
braces). Glue them to some 6mm ply. Cust some more for the ends, and
some for internal if you need it really stiff on both axis. e.g:

https://wiki.diyfaq.org.uk/index.php/File:Torsion_Box_Shelf.png

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 24/09/2023 11:29, Bert Coules wrote:
> On 24/09/2023 11:05, GB wrote:
>
>> I suspect that, even if insured against accidental damage, the
>> insurers  > would be reluctant to pay out.
>
> I'm inclined to agree.
>
>> Can you use the rigidity of the projector's casing to help?
>
> I don't think this is exactly what you mean, but there are ceiling
> mounts which use a central column attached to a flat plate which bolts
> to the projector's underside.  I think they're very inelegant and,
> fairly or not, they don't fill me with very much confidence.  An example:

> https://m.indiamart.com/proddetail/ceiling-mount-projector-15091367473.html

There are a considerable range of projector mounts available - some
verging on the industrial and very strong! (e.g. a Chief VCM101B rated
for 113kg!)

Some projector manufacturers also recommend certain mounts. Do you have
a make/model number for yours, I can look to see if there are any
recommended ones.

>> Oh, and what's wrong with the one in the photo?
>
> The projector in the photo is considerably smaller and lighter than my
> new one, and that 15mm shelf strikes me as just a touch too thin.  Also,
> I can't now remember how I fixed the threaded rods inside the purely
> cosmetic tubing into the shelf so that nothing showed on the underside.
>

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 24/09/2023 13:35, Bert Coules wrote:

> Another thing I've forgotten is what size threaded rods I used:
> presumably, the heftier they are the more rigid the construction will
> be, though I could be completely wrong and something like M8 would be fine.

M12 threaded rod from an electrical wholesaler is very cost effective
source IME:

https://www.tlc-direct.co.uk/Products/UVTR4.html
https://www.tlc-direct.co.uk/Products/FXPW4.html
https://www.tlc-direct.co.uk/Products/FXHX4.html

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 24/09/2023 13:54, John Rumm wrote:

> Or a basic torsion box design...
That would certainly solve any possible rigidity problems but I do like
the open plan look of my previous effort. And ventilation, or the lack
of it, would be troublesome: those projectors generate a fair bit of
heat and need a good air flow around them.

On 24/09/2023 13:54, John Rumm wrote:

> Or a basic torsion box design...

That's a neat idea, thanks. It's constructions like that which make me
wish I had the workshop facilities that American DIYers appear to take
for granted: not only a startlingly full range of saws and shapers all
sorts and sizes but also a large free flat space for assemblies.

On 24/09/2023 15:18, Bert Coules wrote:
> On 24/09/2023 13:54, John Rumm wrote:
>
>> Or a basic torsion box design...
> That would certainly solve any possible rigidity problems but I do like
> the open plan look of my previous effort.  And ventilation, or the lack
> of it, would be troublesome: those projectors generate a fair bit of
> heat and need a good air flow around them.
>
Drill some largish holes through the torsion box underneath the air
grills. However I am sure they are designed to be stood on solid
surfaces so airflow should not be an issue

On 24/09/2023 15:18, Bert Coules wrote:
> On 24/09/2023 13:54, John Rumm wrote:
>
>> Or a basic torsion box design...
> That would certainly solve any possible rigidity problems but I do like
> the open plan look of my previous effort.  And ventilation, or the lack
> of it, would be troublesome: those projectors generate a fair bit of
> heat and need a good air flow around them.

Sorry if I was not very clear, I was actually suggesting the box was
just the lower panel (i.e. the strong light weight replacement for a
large sheet of ply/mdf etc) - not the whole assembly.

(I drew it "open" so you could see what was inside!)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 24/09/2023 15:22, Bert Coules wrote:
> On 24/09/2023 13:54, John Rumm wrote:
>
>> Or a basic torsion box design...
>
> That's a neat idea, thanks.  It's constructions like that which make me
> wish I had the workshop facilities that American DIYers appear to take
> for granted: not only a startlingly full range of saws and shapers all
> sorts and sizes but also a large free flat space for assemblies.

Torsion box style panels etc are very easy to make from the point of
view of tools - anything can cut battens to length, and thin ply.

You do make a good point about having something flat to build on though.

(Although I expect for something in the order of a square meter or so,
it won't be that critical)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

Bert Coules <mail@bertcoules.co.uk> wrote:
> I'm building a suspended shelf which will hold a hefty (14kg) video
> projector. There's a picture of a previous, less substantial, version
> at https://i.postimg.cc/50SpJd4C/Proj-mounts-etc-021.jpg
>
> Fixing it securely to the ceiling joists will be no problem but I wonder
> about the shelf itself: a sheet of, say, 18mm MDF or similar will add
> substantially to the weight of the whole thing.

Serious question, is weight really an issue?

The ceiling joists I dare say will be more than strong enough and a good
solid bit of timber wouldn’t look amiss.

Tim

--
Please don't feed the trolls

On 24/09/2023 15:37, John Rumm wrote:

> Sorry if I was not very clear...

You were perfectly clear. I was simply somewhat stupid.

Bert

On 24/09/2023 16:40, Tim+ wrote:

> Serious question, is weight really an issue?
You must not have seen my previous answer to that: when you're working
on your own and have to hold something up to the ceiling while
simultaneously securing it to the joists, weight is most definitely an
issue.

Bert