18MM or 22MM MDF??

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Iestynd

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Hi all,

I'm after some advise please. I've been asked to make some semi fitted furniture for my brother. They will paint it.

The first thing is a BUNKET type cube system. They have 2 kids (teenage) who want to be able to sit on the top of it - I think 100mm dense foam would be suitable. I have also convinced them a back rest would be better than the wall (as per the drawing).

I will extend the back panel up high, and then add some wedges at the appropriate angle, and then tack another bit of 18mm MDF over the top of the wedges to give a sort of false hollow drum style back. Which again will get foam upholstered and stuck with Velcro.

So, my big question:
In order to sustain the weight of 2 kids would 18mm mdf work? or do i need to upgrade to 22mm?

1655564258996.png



The bottom board will sit under the uprights..... the top board will sit ON top of the uprights so the support is is there for a top weght.
The uprights forming the cubes will be the full height and the cube shelves will be dominoed in (none adjustable).

Dimensions - rough idea at this stage. Overall span is 1700mm. Height is 740mm
Gap between uprights is 400mm (roughly)

Any feedback very welcome.

Thank You
 

recipio

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I should think 18 mm will be plenty strong as the weight is taken by the vertical components. 22mm mdf would weigh a ton ! I'm not with you on the back but you want to avoid adding unnecessary weight. Even a 6 mm panel let into a rebate will prevent racking.
 

Droogs

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I stand on an 18mm base in the workshop all the time and it feels sturdier than the step stool thing I have. I'm 108Kg btw
 

Spectric

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Your bigger problem may be to stop it lozenging, there is no triangulation. One solution would be a back panel that connects both vertical and horizontal members.
 

MikeJhn

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Lozenging now that is a new description of Racking I have not come across before, descriptive, but a new one on me. 🤔
 

hlvd

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18mm will be plenty strong, however it needs a back panel to keep it from racking.
Another thing I’d suggest is leaving the front lip off and letting the foam sit flush with the front of the cabinet. Foam will compress and that lip will be painful under the knees.
 

TomGW

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I wouldn’t be inclined to add a raised back rest - it will spoil the appearance for a start. Also with a flat top on the cabinet the angled back rest will be uncomfortable - the base if the seat would need to be raised at the front.
To prevent racking and keep the open appearance I would fit a back panel within the frame in the lower section where it will be less likely to be seen.
 

Iestynd

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I love this forum. Its full o really helpful people - Thank You.

So, i'm a bit confused now, as TomGW states no backrest, as it could be uncomfortable.

I was thinking something like this:

1655714450332.png

To be clear this is not my work. However you can see the angled back rest on top of a flat box.
Surely thats going to be more comfortable than a cushion against a flat wall (2 surfaces at 90 degrees with each other - The wall and the box)??

My plan was to extend the back panel all the way up, then cut some triangle wedges (from 18mm) and fix them through from the back with screws. I can then lay a sheet of mdf over this... would you really not do this and leave it backless?

Thank You
 
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