Large MDF bookcase [built in]

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21 Mar 2018
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I am planning to replace an old bookcase with an MDF bookcase per picture attached.

I am planning to use 18mm MDF for the frame and shelves. I will need to scribe in on the left to match existing coving. I will build a plinth for the box to sit on above a bulky skirting board.

As to the design, I am considering 2 options:

using 2 dividers per row to give support to the shelves [which will be 152 cm wide]

building two or three separate but identical units and fitting them together. The central column/s would be 2 x 18mm thick which might not look great.

Any suggestions as to which would work better?

Also, I would like to make the unit more rigid by adding a back board. I could use ply, chipboard or MDF. I'm think to go with ply as it's stronger than chipboard and not as heavy as MDF.

This won't be a problem on the left hand side, but on the right I am thinking that I would use a bracket attached to the back wall and the inside of the vertical frame.

Suggestions appreciated - cheers, Martin
My first suggestion is to not use the whole width. Leave yourself a couple of inches clearance from the reveal, at the very least. Otherwise, any discrepancy will be immediately and forever obvious, and the bookcase will feel like it is crowding out the window/ door opening. It is usual to leave 9 inches or more.
I’d say two options; build them as columns and butt them against each other, or build them as rows and stack them up. Columns are easier to slap into position, but you have to be a bit careful if you’re going right up to the ceiling. Rows are easier to get under the ceiling, but require more lifting - and they won’t be light at ~1450 wide.

Either way, avoid the ‘double thickness’ where they individual elements abutt by using half-thickness board for those parts. These can just be glued and clamped together, and a capping piece applied to avoid the seam.

All in MR MDF, backs in 6mm staples and glued.

Thanks, Peter - all makes sense. I can see that etting the columns in place could well be tricky.

Is there any reason to use 6mm MDF instead of ply?
Yes 6mm MDF, ply isn't necessary, it will be plenty strong enough and will take paint better.

Have you considered moving the right hand side vertical part left by about 200mm and having cantilevered shelving to its right? These shelves could have the front right corner rounded off. This would add some interest to the piece and help to avoid the crowding that Mike mentioned.

At that width I would definitely add some solid wood lipping to the front shelves, this could be in a contrasting hardwood, or just radiata pine if you want to paint it.
If the shelves are fixed then screws through the back panel into their edge will be fine to prevent sagging at the back but if they are adjustable I'd be putting a second lipping at the rear of the shelf.
This project is similar in concept to this one I built for my daughter:-
Shelve Unit 1.jpg
I used the bottom-up construction method you are considering, ie, building up from a plinth with the vertical supports and then adding the shelf. The vertical end panels were screwed and glued to the shelves which were supported on temporary vertical spacers. This unit was built in 30mm MDF and the shelf span is 720mm. On the end wall (to the left) the span is 1000mm and there I added some supports attached to the wall to support the back edge of the shelves. All the flat surfaces were painted by roller before assembly with screwhead and front edge filling and touching up on completion
This drawing gives some idea of the construction:-
Kates shelves2.jpg
I feel that your proposed use of 18mm MDF over a span of 500mm is a bit on the lean side. I would recommend going to 22 or 28mm which would aesthetically give it a more chunky modern appearance. I would also recommend getting the MDF cut by your supplier.


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