MDF Floating Shelves, 50mm Thick 4800mm long 375mm Depth - Help / Ideas Pls

Discussion in 'Carpenters' Talk' started by evo nut, Oct 17, 2007.

  1. evo nut

    evo nut New Member


    I have been asked to make up some floating shelves.

    The lady wants the 50mm thick ( I am laminating 2 sheets MDF together ) 375mm In depth and an overall of 4800mm.

    The idea is to make 3 sections 1600mm long with the two ends slightly longer so I can scribe them to a wall.

    She wants 3 sets of shelves at 4800mm long.

    My problem came when I got my floating shelf brackets out of my store from Hettich. They are just too small, and also they can't take the weight as each section of the shelf weights 18kg.

    So my idea was to drill, in her solid wall, 3 20mm x 200mm holes, per shelf, thats 27 in total and make a routered groove in the back of the shelf and slide the shelf on to it. Fit the stud in the wall with Gripfill and the hole in the shelf so its goes of nice and strong.

    Seems to me there are a fair few things that can go wrong with this, i.e studs in wall not level, the overall shelf out of level, bowing of the MDF.

    So does anybody have a better idea. Considering that she doesn't want batterns run around her wall, brackets to hold the shelves up or supporting legs of any kind. As well as the fact she doesn't want to spend anymore money, shes paid me £575 already

    And to top it all she wants to but books on the shelves!!

    A bit long winded I know but I was wondering if anybody had a better idea.

    Thanks for your time

    evo nut
  2. chip off the block

    chip off the block New Member

    use resin to ancor stuff in the wall
  3. evo nut

    evo nut New Member

    chip off the block,

    thanks for the reply

    could you give me a name of a product or a link to one if poss?

    do you mean the one made by fischer?

    also do you think metal studs in the wall best way to go?

    evo nut
  4. chip off the block

    chip off the block New Member

    yeah the ficher stuff and its te only ay i can thik of doing it. The problem is the weight of the mdf and books ie paper in 1 of the heaviest things to put o them. How about hanging the front edge from a wire like glass shelves in shop displays?
  5. evo nut

    evo nut New Member

    chip off the block,

    thanks aagin,

    yes wire is a good idea i will ring her tomorrow and let her know.

    the MDF i bought was the lightweight one so i have saved a bit of weight there.

    will let you know what shes says

    evo nut
  6. chip off the block

    chip off the block New Member

    didnt know there was a light weight mdf, so ive been busting my ******** lifting 25mm 10x5 sheets when i could get lighter stuff dang
  7. lamello

    lamello New Member

    you would need some form of torsion box design to counterack the sag. Thats a big span. Rather than laminating two sheets together. That is going to be heavy. Maybe 32x32 frame and clad in 9mm both sides. It will have to be designed well tho
  8. > you would need some form of torsion box design to counterack the sag.

    sure you aint a plastic surgeon?
  9. chip off the block

    chip off the block New Member

    torsion what what
  10. lamello

    lamello New Member

    how about grooving the shelf and allowing a cantilever bracket to sit under the surface at a couple of points and then chasing the wall out to hide it in the plaster. If you know what i mean. Good car filler will make it undectatable on the shelf.
  11. lamello

    lamello New Member

    you can make torsion boxes that by the nature of their design are stronger than the sum of their parts, bit like a bridge.
  12. dirtydeeds

    dirtydeeds New Member

    evo nut. listen to the man

    lamello is giving good advice

    books (calculations for librarys) weigh 35lbs a linear foot thats about 50 kilos a linear metre

    your shelves cannot sag more than 2mm per linear metre otherwise it will be noticed

    bin your 2 layers of 18mm mdf

    buy 6mm mdf and make up a torsion box with a total thickness of 50mm. make the torsion box skeleton of real hardwood

    bring your shelf supports in to 900 centres

    THEN fix as suggested above
  13. jasonb

    jasonb New Member

    Torsion box is the way to go, I would use two layers of 12mm with some batten along the front edge and at intervals front to back like aeroplane wing ribs, face the front with some thin MDF.

    12mm metal dowels resin bonded into the wall and 14mm holes in the shelf/wall to give a bit of adjustment.

    Have a look at this pic and the next two for how I do it with built up shelves. Or painted ones from here onwards

    The problem with the Hafele, ikea etc brackets is that you are still just hanging th eshelf from screws.

    The lightweight and ultra light weight MDF is OK where it does not need a machined edge or routed detail because it is very "Fluffy" and you cant get a decent finish to the fibres.

  14. Mr Mike

    Mr Mike New Member

    I did a job exacly the same last year.

    After asking on here, I followed Jason B's advice.

    The shelves are still stacked full of paperbacks and doing fine. I was building some alcove cupboards for the same lady last week.

    The method was an MDF sandwich (yummy), 18mm + 12mm + 18mm. The 12mm middle had slots cut out to receive 12mm threaded rod that was anchor resined into the walls using the screwfix polyester anchor resin. They were spaced every 4-500mm as I remember.

    To join the shelves to make the long span, I made the 12mm the tongue and the 18mm the groove (end to end I mean).

    It all worked fine. Genuinely the only way you can see the join is a hairline crack in the paint where the span's join, I noticed last week. Apart from that no sagging, etc. Customer was very happy.

    I can't speak for Torsion boxes, but I know they work, and if I'd tried harder at Physics at school, I'd probably understand why they worked too.
  15. Mr Mike

    Mr Mike New Member

  16. paulo333

    paulo333 Member

    I do this a bit differently. Basic tortion box idea but getting it's support from a cross-bar at the front rather than rods resined into the wall. As follows:

    Depending on the final thickness of shelf wanted, batten the alcove along the back wall and both sides with 1"x1" or 2"x1" (or 2"x1" ripped to whatever size you need). Make sure the side battens are well secured - especially near their front edge. Glue and screw them if in doubt. Then fix a front batten securely into the side ones. I use 2" or 2.5" screws.

    To this batten I already fixed metal rod on it's back edge - the cheap pre-drilled stuff 30mm x 5mm from most builders yards works nicely onto 2"x1" for a thicker shelf. Thinner shelves need a different type of rod - major DIY stores do a bunch of types although it costs a bit. The metal eliminates any sag.

    Fit some intermediate cross pieces. Sandwich 6mm, 9mm, 12mm MDF or ply (or a combination) top and bottom to make up your thickness and edge the whole lot with a nice hardwood strip across the front.

    I've done quite a few like this now and they are very strong. One lot of 1.8metres span took full loads of large books no problem.
  17. evo nut

    evo nut New Member

    chip off the block,

    yes i dodn't know about it for a while but the lighter is better but harder to get a good finsh on the front edges.

    evo nut
  18. evo nut

    evo nut New Member


    thanks for the reply.

    by a torsion box do you mean a stud frame fixed on the back wall with noggins in between.

    this is what i think is best but the customer isn't so keen.

    evo nut
  19. evo nut

    evo nut New Member


    thanks for the reply

    she doesn't wnat anything to do with brackets for some reason even if i do chop them in to the wall!

    evo nut
  20. evo nut

    evo nut New Member

    dirty deeds,

    thanks for your reply.

    your advice is very helpful i thank you.

    i don't want them saggin.

    i think the box idea is the best with studs in the wall, will have to persuade her a bit, as she seen what she wants in a magazine, well that helps me --- not! and they are about half the size not over 4m long

    evo nut

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