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I will be making my first cabinet out of MDF, taking inspiration from a product I have seen, also made out of MDF.

It won't be anything fancy, as you can see from the simple diagram of the join below. Corner piece join diagram

I know MDF is considered to be rather weak when it comes to joining at the edges, so I was wondering what the best method of joining pieces like this together? Pocket holes, dowels?

Dowel join pocket hole

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6
  • "I was wondering what the best method of joining pieces like this together?" Late to the party but I was going to say depends who you ask, and if you posted this question on a busy forum you'd definitely get a split in the answers. FWIW I think there's little or no functional difference between the two options you illustrate, either one would be strong enough for service if the thing is made well, and glued well.
    – Graphus
    Jan 15 '20 at 6:43
  • @Graphus - "if the thing is made well", seems that you are aware of my prowess for messing things up XD. But yes, I know that it would be a controversial decision depending on who I ask. Might be that I invest in a doweling jig or perhaps go the rabbit route.
    – physicsboy
    Jan 15 '20 at 7:25
  • ^_^ Re. a dowelling jig, if you're up for a bit of DIY it's easy to make a simple one that could be used for a couple of projects from just a small cutoff of wood and a piece of hardboard. Or just two pieces of wood, hardboard is used to make the thing more compact and no other reason really.
    – Graphus
    Jan 15 '20 at 11:44
  • By the rabbit route do you mean a rabbet/rebate for the end of the joining piece to sit into? This is worth doing for alignment reasons if nothing else but actually doesn't add a huge amount of strength. When I do it I nearly always reinforce in some way, usually by pegging in my case. Nails or screws were the most common historically but that was for solid-wood construction, for MDF they're both possible still but I'd go with pegs or hidden dowels by preference I think.
    – Graphus
    Jan 15 '20 at 11:47
  • @Graphus Thanks for the advice. I've gone for a Wolfcraft jig. A little more expensive than the cheapy-cheap ones, but I've seen the video of it in use and it seems to be quite good for aligning adjoining holes, and it looks pretty compact in itself.
    – physicsboy
    Jan 16 '20 at 8:58
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MDF is different than normal wood, in that there is no end grain vs face grain. Since MDF is all just basically sawdust combined with a resin, any surface is as strong as the other for gluing.

It may well be that a properly glued, clamped, and cured joint may be plenty strong for what you want. It will depend upon where the stress is being applied. My guess is that with either dowels or pocket screws, the surrounding material will fail before the fastener will, so you can most likely get away with either. Dowels will probably be slightly stronger, but more of a pain to do correctly. Pocket hole screws will be much faster and not require clamping while the glue dries.

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  • Thanks for the advice. I worked with MDF a while back and had trouble with its rigidity near the edge so was just being weary. Looks like I'll have to buy myself a pair of big boy clamps!
    – physicsboy
    Jan 14 '20 at 20:33
  • I read an article once that tried to compare dowels and pocket screws, but the material tested was regular softwood. If the joint was screwed and glued the joint would fail sooner than a doweled joint, though the failure point was the head of the screw. I suspect the failure mode for MDF would be similar for both, with a plug of material being pulled out by the dowel or screw. But I am unable to find a similar sort of test using engineered wood products.
    – jdv
    Jan 14 '20 at 21:41
  • Screws can be iffy in MDF I would go with dowels
    – Monte Glover
    Jan 15 '20 at 0:38
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    Re. MDF and grain, Does MDF have a grain direction?
    – Graphus
    Jan 15 '20 at 6:46
  • The dowels or screws for this sort of construction are often to keep the slippery glue line straight, really. They are a bit of insurance.
    – jdv
    Jan 17 at 0:16
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I would definitely recommend the dowels. The greatest stresses will be in tension trying to pull the boards apart and breaking the connection of the screw or dowel with the boards. Both the dowel and screw will be stronger than the boards. Imagine pulling up on the horizontal board in your illustration. All the rotational force will try to pull the screw out of the board and it is only resisted by the surface of the board in contact with the screw (a very narrow width of board). The dowel on the other hand has much more surface area in contact with the board and will distribute the load over a broader contact area.

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  • "rotational force", now you're speaking my language! I understand what you mean by the dowel being the best route here, thanks for the advice.
    – physicsboy
    Jan 15 '20 at 7:29
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I use biscuits in this situation, not for strength, but because wood and mdf likes to move when glued, even when clamped. The biscuits align the piece so the edge is clean. Dowels would do the same job but hard to align if using a drill - router and fence is better. Pocket screws have the same issue.

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I'm looking into learning how to fasten butt joints of mdf as well. I watched a useful video by woodworking YouTuber Steve Ramsey on using pocket screws for this purpose.

It points out that the screw should not point toward the end of the receiving piece.

So this:

     ________________
    |_ /_______________
    |/  |
   /|   |

is better than this:

     ________________
    |\_______________
    | \ |
    |  \|
    |   |\
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  • 1
    But this makes hole to fill is on outside
    – Volfram K
    Jan 16 at 7:31
  • Could you edit to include some attribution to that link. Many people will not follow blind links, reducing the usefulness of an Answer that includes one.
    – Graphus
    Jan 16 at 18:40
  • @Graphus it is a YouTube link, at least, not SomeRandomWebsite.com...
    – FreeMan
    Jan 17 at 12:16
  • @FreeMan, yes, but to which channel? The prospective viewer might remember they've already seen it and don't want to open it again for example. Better reason: someone might not want to view a vid from a particular content creator, e.g. because they've already told YouTube Don't recommend channel about fifteen times!!! [This just happened to me today, again, for about the zillionth time *sigh*
    – Graphus
    Jan 17 at 17:08
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    ...YouTube inundates your recommendations with more of the same, like your 5+ years of watching another topic didn't happen. DAMHIK. And it's not like their on-topic recommendations are famous for being good, I don't know if you know the channel but Workshop Companion (Nick Engler's channel, an author I knew and liked) had never been shown to me before about four days ago. Grrr,
    – Graphus
    Jan 17 at 17:27

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