MDF construction tips

Discussion in 'Carpenters' Talk' started by Hambone, Mar 22, 2006.

  1. Hambone

    Hambone New Member

    Hi! I'm new at this, and am building two DJ roadcases from 15mm MDF. I've had the MDF cut to size, and I'm ready to start putting it together. I'm looking for advise from you pros out there! It needs to be strong for road use.

    Right now, my plan is to screw and glue L and T joints with MDF screws and wood glue. Some of the MDF screws claim to not need a pilot hole and are self-countersinking, but I thought it better to drill pilot holes the same diameter as the shank of the screws, squirt glue in before screwing them together, and countersink the MDF before putting the screwsin.

    Someone also mentioned using plastic blocks on the inside of the joints for mroe reinforcement.

    Thanks in advance for any help!
  2. Jonny Round Boy

    Jonny Round Boy New Member

    You'd be FAR better off binning the MDF & using a good quality ply. You can make very strong boxes with 12 or even 9mm ply - they will be a lot stronger, longer-lasting, and lighter that any MDF box.

    Your construction method seems fine, though I wouldn't bother with the glue in the screwholes - you may find it just makes the job harder. Glue & screw the joints as you describe, and if you want to make them extra-strong, put a 6mm fillet of epoxy resin round the inside of all the joints.

    I know you've already bought the material, but MDF really isn't the best thing to use.
  3. Hambone

    Hambone New Member

    Oops... I already had the MDF cut. I should've come here first!

    I know they're gonna weight a ton, too. I have a feeling I'll end up rebuilding them once I figure where things are best situated, so I don't really mind.

    I'm putting them on 4" castors with rubber wheels, and I actually thought the extra weight of MDF would help stop the boxes from bouncing around in the trailer with computers & other fragile stuff in them.

    Thanks for the info!
  4. big all

    big all Screwfix Select

    heeelllooo ham bone and welcome

    as above ply is more robust
    as you have to use mdf this how i do it with screws and mdf

    [assuming its half inch-12mm]mdf i use 6x1.5"screws a 3 or 3.2mm drill avoiding the 30mm each end

    butt joint the components screws every 50 to 75mm pilot the full depth of the screw through both components
    use the pozi srewdriver bit for your countersink glue and screw together hand tighten the last 2 turns

    if the edge does delaminate slightly push glue into the crack ,unscrew the screw a few turns block and clamp then tighten screw

    clear as mud

    big all
  5. Bonzo

    Bonzo New Member

    Agree ply would be better. If I were making these I'd go along with the blocks idea but instead of using blocks I'd use full length 1"x1" pine, or similar, in each corner. Glue then screw thro' mdf into pine, that way you will not have to screw into mdf edge and have a greater glueing area.
  6. Hambone

    Hambone New Member

    Thanks for the welcome!

    I just picked up the 15mm MDF from being cut (damn... these things are gonna be heavy!)

    What about these screws:

    Many of the joints are "L" joints. When you say avoid the 30mm each end, does that mean I can't make "L" joints?

    Should the pilot hole be bigger on the flat piece so it doesn't split, and then smaller in the end-on piece where the threads will be?

    Thanks again for the help!
  7. Hambone

    Hambone New Member

    The pine batten idea sounds like a good one. I thought about that before. Less risk of splitting the MDF.
  8. big all

    big all Screwfix Select

    i would also go with full length battons if you have the space

    the 30mm is
    when you butt join the two edges you drill your screw holes centraly in this case 7mm from the edge along the whole length
    but as you get towards the ends they may start to delaminate hense avoiding the last 30mm
    you can go closer to the end but the risk is then greater of delamination and also if your joining 3 bits together on a corner your screws may interfere with each other

    would also suggest you place a couple of 20by44 planed timber battons on the bottom for protection if theres going to be any sliding or banging[but only if they would fit in ]as i dont actualy know what a d j box is!!!!!!
    i am assuming its for records!!

    big all
  9. Hambone

    Hambone New Member

  10. Scrit*

    Scrit* New Member

    Havu=ing built kit boxes in the past I'd recommend using steel corner protectors and aluminium or steel L-profiles at least on the bottom edges.

  11. Hambone

    Hambone New Member

    I saw PVC C- and L-channel extrusion when I picked up the MDF. Aluminium or steel sounds a lot better, though, along with the corners.

    Thanks for the tip!
  12. big all

    big all Screwfix Select

    scrits idea is the way to go angled metal wide enough to accomodate all the bolts for the castors

    i can see several possible problems
    securing castors to the mdf is likly to pull the box to bits before the years out
    so if you build an oblong frame[perhaps dexion type stuff] held together by the bolts securing the wheels on
    then secure the frame to the boxes

    dont forget mdf dosnt like getting wet it just swells up
    try leaving a coffee or tea cup with a wet rim on it for twenty mins remove cup and dont dry it
    tommorow youll have a raised ring
    so make shure you paint it well and keep it dry

    and oooooooooo the weight ;)

    big all
  13. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    If you change your mind and use ply, remember this.

    Ply don't like being srewed into anywhere near the edge, and that include going into it endways.

    I definitely agree with the corner strips of some kind, and you are correct in thinking pilotholes(thread-size for the through-piece and a tad under shaft-size for the thread to screw into.

    Not sure about the castors. I would put thin coachbolts down through the inside of the floor, then nut outside, then put a thin flooring on top inside to protect the contents from the boltheads.

    Mr. HandyAndy - really
  14. Hambone

    Hambone New Member

    If I hadn't already spent £75 on four sheets of MDF and had it cut, plywood it would be...

    The castors have a metal plate for mounting, and I think I'll put another metal plate on the other side of the bottom, then lockwashers and nuts. The 15mm MDF is pretty sturdy, and the large 4" wheels with rubber tyres should help to make it last. Metal L-angle wide enough to mount the castors on would have to be huge. Another option would be to use plywood for the base. I could always use the piece of MDF for another shelf or another project.

    Regarding painting, what's the best option? It needs to be black, and it sounds like waterproofing would be a good idea. What's another kilogram of paint when it already weighs a ton?!

    Thanks again for the advice, everyone!
  15. Hambone

    Hambone New Member

    You guys were right... MDF ain't the stuff to use!

    It weight a ton, and the drill goes through it like a hot knife through butter.

    I'm gonna stop right here and start again with plywood, either 9mm or 12mm.

    Anyone want to buy some 15mm MDF cheap?
  16. Scrit*

    Scrit* New Member

    In that case make sure you get a good quality plywood - I'd recommend birch ply, not the cheapest but good - and specify a WBP or exterior grade. Also use steel or wood backing plates inside wherever you attach handles, castors, etc to safeguard against pulling through.


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