MDF screws

Discussion in 'General Chat' started by Keiron, Feb 6, 2014.

  1. Keiron

    Keiron
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    Not the most thrilling of topics!

    Does anyone know what screws I should use for MDF?

    I’m making a sort of box our of 18 mm MDF. I’m joining the corners with glue and right angle brackets. I really want to screw the brackets in with countersunk screws, but I’m not sure what screws to use (I know that MDF doesn’t take srews very well, so maybe I need to drill a pilot?) and in any case, the only ones I have seen seem to be very long, whereas I only need short ones so they won’t poke through the 18mm MDF.
     
  2. stephenbarnes

    stephenbarnes
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  3. Keiron

    Keiron
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    Thanks. I had found them on Google. But the shortest they do is 40mm, whereas i am looking for something more like 15mm.
     
  4. IronGiant

    IronGiant
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  5. blue max

    blue max
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    15mm is not very deep, even if all of it goes into the mdf. It is really quite fragile.
     
  6. k17chy

    k17chy
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    Definitely need to drill pilot holes as the mdf will split.
     
  7. blue max

    blue max
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    And a dribble of wood glue to bind it together. Maybe experiment a bit before you commit.
     
  8. IronGiant

    IronGiant
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    It would be stronger if he got longer screws and went all the way through the board and then cut off the excess length where it poked through. But then he has to tidy up the finish. Using internal angle brackets probably isn't the best way to build a box out of MDF. It's more common to screw through the face of one board (countersunk) into the edge of the neighbouring board with at least 40mm long screws. And then fill in the countersinks. That's how most of the subwoofer box builders do it.

    It might help if you said what the box was for?
     
  9. blue max

    blue max
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    I see what you want to do. I would build your box and then double up the thickness by adding additional pieces inside. That help help support the shape and keep it square. It will also give you some material to screw into. And suppress the sound better as a bonus.
    Hope that makes sense - not easy to explain!
     
  10. Keiron

    Keiron
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    So is doing "butt joints" with long screws (and glue), stronger than mitred joints with brackets and short screws (and glue)?
     
  11. IronGiant

    IronGiant
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    I would say so. Better yet, as Blue Max suggested, put a piece of 1" by 1" timber in each corner and screw through the MDF into that. With glue over everything except the carpet :)

    You could still use mitred joints with that method if that is what you fancy.
     
  12. blue max

    blue max
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    I would not try to mitre mdf myself.

    This is what I'd do - very rough, but think it would work well.
     

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  13. IronGiant

    IronGiant
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    Ah, I see you weren't suggesting 1" battens then :)
     
  14. blue max

    blue max
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    That would do, but it depends on how big the box is really. And how much mdf you have :)

    Might start to get a bit weighty too!
     
  15. 27neth

    27neth
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    Dont mitre it and use angle brackets.. The strongest way would be butt joints with glue and screws.

    John.
     
  16. oska

    oska
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    Back in the day I used to make my own car bass boxes out of 18mm and they would be solid with butt joints using glue and some screws. I used to use Wurth Pozidriv screws and wood glue. Any decent wood screw with a tightish thread should be fine.
     
  17. Keiron

    Keiron
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    I set about doing this this morning. I can't believe how difficult it is (or how I am making such hard work of it).

    I am trying with butt joints and longish screws.

    I am finding it impossible to get a flush finish. It's as though I need a jig to hold it all together while drilling.

    Secondly, the mdf splits whatever I do. I have 4mm screws and even with 4mm pilots, so the screws are only effectively holding it lightly while the glue dries, and the mdf still splits.
     

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