Advice: built-in Cupboards/shelves Torsion box construction

[Mike.S]

All

I am currently designing/planning the construction of two lots of cupboards and shelves, plus a desk, to fit into the alcoves either side of the chimney breast in our dining room. Current design looks like this:

Each alcove is approximately 2.6m high by 1.3m wide and the desk extends 1.7m from the far wall.

I would greatly appreciate any observations, suggestions or even criticism (hopefully constructive) of the design and/or proposed construction method.

Carcass, shelves and desk all to be made from 50mm thick honeycomb boards (torsion box style) using either 6 or 9mm MDF skins with the core filled with 32 or 38mm cardboard honeycomb such as this. This will form a torsion box like this (pic from Dufaylite):

I propose to add framing around the edges and internally where needed e.g. hinge recesses in cupboards. From my research so far the framing materials suggested are MDF, Chipboard, OSB and timber (soft or hardwood). Requirements for such a material are that it should be stable (no twisting/shrinkage), 'glueable' and accept drilling/machining (dowels, biscuits, hinge holes/screws etc) and available in necessary dimensions e.g. 38mm if 2 x 9mm skins used. Finish will be paint - possibly high gloss white. All fixings/joins to be hidden/invisible. I'm a reasonably competent DIYer but this is all new to me so would welcome feedback, particularly on:

1) best framing material: for ease I could use say 2 x 15mm MDF which would give me 48mm (near enough to 50mm) overall thickness but am uncertain about screw holding strength. Chipboard -same concern and general aversion from past experience as a consumer. My preference, I think, is softwood as I can dimension it (P/T available), affordability etc but am uncertain as to its stability. Would kiln dried structural timber be OK e.g. 100mm x 50 nominal?

2) Cupboard doors: these will be flush with the carcass and minimal clearance desired for aesthetic reasons. Will 15mm MDF be robust enough or 18mm better? Two hinges per door which I'd like to be adjustable (up/down and in/out) - which type? Push-to-open catches - 1 per door? Again, any recommendations on manufacturer?

3) Joining: glued butt/mitre joints unlikely to be strong enough so some kind of mechanical fixing required. So I need to consider dowel versus biscuits (or splines) versus ?? Thoughts on pros and cons welcome. I do not currently have any dowel jig or machinery (Domino or other) so will acquire what's necessary.

4) Machinery: I have a bandsaw and C/S but neither is ideal for ripping boards with a straight edge, so am considering a track saw rather than a table saw, especially as my work space is limited (probably the dining room table!). Makita SP6000 ahead of the Festool 55/75 on value for money grounds. Am I thinking straight or will a (small) T/S also be needed?

Sorry, it's a long post but want to get the design finalised and my thinking straight before ordering stuff.

 

[Chrispy]

Are you thinking of makeing your own panels or buying in ready made? if your makeing how are you going to glue them up? It's not impossible but not easy either.
I'm also keen to know how your going to get the high gloss finish.

 

[Mike.S]

Chris

Planning to make my own panels. I did consider buying in ready mades but whilst you can specify framing round the edges of each panel it is harder to incorporate internal framing e.g. to allow for a hinge recess. My inspiration came from watching some one else do it:

See here, previously posted by ondablade.

As far as gluing it seems any of the usual glues work e.g. PVA, Cascamite and you just use a roller to apply it to the skin then place the honeycomb over (with additional fixings - stapling will do - at the sides/ends). The flexibility this provides is welcome. I haven't discounted using ready made boards in a hybrid system. Difficult to describe but essentially the honeycomb board can be cut to fit between the framing members and then the skins applied. This would be easier to handle (the honeycomb is already expanded) and board facings can be anything from thin cardboard to MDF. On cost grounds the cardboard facing is cheapest (Dufaylite call it UltraBoard R) and can be easily glued to the planned MDF skins.

Likely to make up my own clamps (Diego style - see link above) as commercially made ones are too expensive (I'm not a pro likely to re-use them frequently).

The finish isn't decided yet and will post further if I decide to follow this route. I like the high gloss finish but it does entail many coats (spray gun on my wish list) and much sanding.

 

[Phil Pascoe]

The wall is probably an external one so even if it's cavity it would probably pay to keep some form of ventilation behind any enclosed cupboards and even bookshelves - these things are damp magnets.

 

[Mike.S]

Thanks phil - the sort of thing I hadn't considered. The r/h wall is external and I suppose the chimney breast itself may wick some moisture via the flue (open at top). The rear wall/chimney breast is a party wall and the l/h wall is internal.

There will be a backing board behind the shelving but there will be airspace (possibly only 5-10mm) between the board and wall, so hopefully that's sufficient for ventilation. Also, the boards will be sealed all round, even on unseen faces (sealer and/or primer as a minimum) so I hope damp won't become a factor.

P.S. My original post should have said 32mm honeycomb board (not 38mm) to give 50mm overall thickness if 2 x 9mm MDF skins are used.