How to fix these shelves?

[Harrier23]

Amateur DIYer about to start next project.

I'm looking to put built in cabinets and shelving in my living room alcoves, similar to the photo attached.

I'm comfortable with building the cabinet and plan to build the shelving above in situ.

I plan on using 25mm MDF for the vertical partition and shelves.
I'll fix 25mm MDF to the walls on either side and then a board at the top which will will eventually be covered by trim.
I'd fix the vertical partition by screwing upwards from inside the cabinet and down through the board across the top.

Where I am a bit stuck though is the shelves as I won't have access to screw these in from the outside.
Would sinking screws at an angle and covering with filler be the best way? From experience I've struggled to fully sink the screw when doing this in the past.

Ideally I'd want to avoid having any visible brackets if possible.

On a side note, the width of each shelf will be around 640mm. Would I likely see sagging at that length if using 25mm board or should I be ok?

Thanks for any advice given.

Dan

 

[freddiemercurystwin]

Would you not build the whole shelf unit as a complete box on the floor ie like you would a kitchen cabinet and then fix it back to the wall, supported on the base units? They'll be no sag with 640 wide shelves.

 

[jj4091]

Dowls and glue ?

 

[Harrier23]

I suppose another option would be to make the partition and shelves out of timber (thinner than 32mm ideally) and 'wrap' this with 6mm MDF. This would solve the side fixing issue but would mean slightly chunkier shelves

 

[freddiemercurystwin]

I don't really understand the side fitting issue, if you build the units beforehand.

 

[Harrier23]

I don't really understand the side fitting issue, if you build the units beforehand.

My only issue with building separately would be gaps at either side if the chimney breast wall isn't perfectly straight. Something I'll need to double check.

Let's say I did manage to build it separately, I'd still have the issue of fixing one of the shelves to the vertical partition

 

[freddiemercurystwin]

You build a back on to the unit and screw through that. For the sides you would fit an architrave over and scribe it to the inevitably uneven walls.

 

[foxhole]

18mm mdf would be easier and cheaper .

 

[Harrier23]

18mm mdf would be easier and cheaper .

I considered 18mm but wasn't sure if it would be strong enough for the shelf width

 

[Koolpc]

You build a back on to the unit and screw through that. For the sides you would fit an architrave over and scribe it to the inevitably uneven walls.

This

 

[freddiemercurystwin]

I considered 18mm but wasn't sure if it would be strong enough for the shelf width

Yes plenty strong enough, only need to use 25mm for those spans if you wanted a more chunky look.

 

[big-all]

Dowls and glue ?

this only works if a freestanding unit slotted in as a say 35mm dowel needs a minimum 20mm extra width for dowel insertion and an angle off approach as 18mm dowel sticks out both shelve ends requiring slot in one end then close up other end this method wont give fixings essential for support along the back panel
in other words, only a freestanding unit the correct width will work with allowances for deviation in both sides
i personally would look at 12mm sides and shelves with 6mm back unless very heavy loads assuming shelves supported along the back at perhaps 100-150mm spaces
as the sides will have infills you could go for 12mm sides 18mm shelves and 6mm back to give the chunky look with minimum lost space
yes you could go for 18mm sides and shelves for maximum material use but will weigh a ton
what exactly are you planning on the shelves??

i have made many dozen off shelve or storage always 12mm with above 700mm halved with a central partition with use off no6 2" screws with 3mm pilot being my fixing off choice with glue never failing as mdf will not delaminate iff correct precations taken

as an aside with a central partition you have dowel one side and screw the other