I am making shelves for shoes using MDF boards. The place where I want to mount them is between two wooden pillars of the staircase, so I thought about having the planks a little larger than the space between the pillars, and I made a cut-out for better appearance.

On the underside of the planks (shown in the photo) I made depressions where I can put iron flat profiles so that they are less visible from the side. I planned these profiles to strengthen the connection to the pillars, otherwise in case of stress or hits the MDF would not hold with only a small connection (screws) in the middle.

The planks are ready, but I realised late that I cannot glue the iron profiles to the slots as I planned, otherwise I would not be able to tilt the planks when I install them, due to the L metal supports welded to the iron strips.

enter image description here

The available thickness of the MDF is 6 mm, the thickness of the iron strips is 4 mm.

How can I fix those profiles to the boards? or, are there other alternatives to fix the boards to the pillars in the cut-outs?

I was thinking about using these "Euro screws", length 9 mm (1 mm less than the available material).

Besides the issue with these screws being 6.3 mm in diameter including the thread, while I have only 6 mm or 7 mm drill bits for the iron strips, my issue here is that I need to stop drilling 1 mm before the end of the MDF, to keep the appearance on the top side, but drill bits for wood have a quite long central spike, and metal drill bits have a conical tip which is not suitable: either: the center of the bit would need to go more than 1 mm further than the sides.

I think I could find a bit for routers, which have a flat cutting surface, but a router is not accurate enough (I think) for drilling exactly where I need it to be. A solution would be to apply the router drill bit to a column drill, and stop "drilling" 1 mm before the end of the MDF.

I will need an incredibly accurate placement of the holes compared to the metallic strips, but it may be doable.

  • Do you really need to fix them? Would it be a problem to just let the planks rest on the iron profiles? Sep 16 '20 at 11:24
  • @ThierryLathuille What if someone bumps into the planks? they are placed in the entrance of the house and not everyone is always very careful, not to mention guests. I could glue them after fixing the supports to the pillars but then I'm stuck if I need to remove them, they would need to be broken
    – FarO
    Sep 16 '20 at 11:29
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    As long as you can drill clearance holes for the screws you plan to use (and the 7mm screws should give ample clearance) I think you should be fine here. Placed where they are these screws may not absolutely need pilot holes, although they are advisable.... do ensure the pilot holes are not too large! If you're worried about drilling too deeply by all means drill the holes slightly shallow. On MDF and chipboard/particleboard, as well as softwoods, I regularly under-drill pilot holes and allow the screw itself to complete biting into the material, which they can do without any difficulty.
    – Graphus
    Sep 16 '20 at 18:40
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    Have any scrap MDF of the thickness you're using? Test on that rather than directly on the project pieces if at all possible. Sorry I didn't look at the link to the screws previously, given these have no point you do have to drill full-depth pilot holes for them. So you're going to run into difficulty unless you grind a custom drill bit (which is doable, but hardly ideal). I think choosing different screws may be the best idea here, e.g. of the panhead type @SaSSafraS1232 mentioned previously. With these you also don't need to worry about doing countersinks on the steel.
    – Graphus
    Sep 16 '20 at 21:33
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    I'm having a hard time envisioning where these shelves go. I'd greatly appreciate a pic or two of the finished installation!
    – FreeMan
    Sep 17 '20 at 12:39

It sounds as if drilling the holes for the screws as well as making the screws work at all, may be more effort for you than it's worth. You definitely aren't going to make this work by buying a router bit for your drill.

You said you thought glue might be strong enough (and many types would be extremely strong) but you're worried about possible future disassembly problems using glue.

Why not try this: Get some good 2 sided tape from one of the woodworking supply stores. Rockler and Lee Valley Veritas both carry types meant for attaching to wood products. It's used all the time to temporarily attach wood to jigs and fixtures. You don't want the micro thin stuff. It likely wouldn't have enough thickness and give to make a good connection between the course MDF surface and your brackets. Lee Valley used to have a type made with a layer of interwoven threads between the 2 sides. It is very tenacious.

Be sure to sand or scrape the MDF surface smooth and remove any and all sanding dust from the wood. Wipe the mating metal surface clean with some alcohol, and press fit them together. Allow 5 to 10 min. to be sure it's stable and you should be good to go. Accidental bumping should not affect them at all. If the day comes you need to move or disassemble them, A few minutes with a hair dryer should soften things up enough to peel them apart.

  • Good idea! I'll go for this first, looking for more complex solutions only if needed.
    – FarO
    Sep 17 '20 at 8:56
  • There's a thin, foam-based, double-sided sticky tape (maybe made by Scotch?) that is super sticky. It might work well for this. Sep 28 '20 at 20:54

How can I fix those profiles to the boards?

Use magnets. Use a router or drill with forstner bit to excavate space in the shelves just above your brackets, and then epoxy rare earth magnets into that space. You can add as many as you need to attach the shelf firmly, but you'll still be able to remove the shelves if needed.

  • Nice idea! I'll see if I have enough, otherwise I use the tape
    – FarO
    Sep 25 '20 at 6:39
  • Now I feel thick, why didn't I think of that??? Geez, it's not like I haven't already made a few things with inset magnets :-|
    – Graphus
    Sep 25 '20 at 7:05
  • @FarO, it's good form for you to upvote all the Answers you think are helpful.
    – Graphus
    Sep 25 '20 at 7:08
  • @Graphus I'll accept an answer and upvote the other useful ones after I do the testing
    – FarO
    Sep 25 '20 at 20:47

You could use threaded inserts similar to this if you need the shelves to be held together with screws. enter image description here

The smallest of these would require something like filing them down to 9mm, but I don't think that would affect the functionality of the inserts.

The insert that you want for MDF is the one on the extreme left in the picture--the one with the extremely course threads on the outside. They are made to go into MDF and "bite" better than standard screws. The other two inserts pictures are for different applications. You don't want those.

  • But then why not screws directly in the MDF?
    – FarO
    Sep 25 '20 at 20:47
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    Primarily because the threads on the inserts are made to go into MDF and hold better than wood screws usually do. The fine threads on screws tend to strip out easily in MDF with a little provocation. If you add a touch of epoxy to the outside threads of the inserts when you install them, they will hold "forever" no matter how many times you take the screws in and out or bang the shelves around. Sep 25 '20 at 20:52
  • Oh to be clear, 9 mm is the screw length, which means iron+MDF. The insert I need should be 5 mm long, which makes it quite challenging in my case. But the idea and the advantages are clear to me for future projects!
    – FarO
    Sep 25 '20 at 22:00

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