Simple niche/nook shelf: boards resting on screws

boarderror toleranceloadscrewsshelf

I have a niche/nook in a room (marked red)

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and some leftover chipboards of width 16mm. Together they should make a simple shelf. So I would cut the chipboards to the same width/depth as the niche/nook (minus some mm) and for each board

  • drill 4 holes to the opposing sides (marked blue) at a certain height
  • put rawplugs/screw anchors and screws in the holes
  • put the board on top of the 4 screws.

The wall is made of concrete (right side) and bricks (left side).

Questions:

  • What types of screws should I use (thickness, material) so that a board can carry up to 10kg? The weight will not be concentrated on one spot, it will be distributed quite evenly. E.g. one board should carry a basket (almost same size as board widht/depth) which will be filled with empty glasses and bottles.
  • What options do I have to compensate inaccuracy of the drilled holes? I never manage to make all holes on the exact same height, or to make all of them perfectly horizontal!

Best Answer

Almost any good quality 5mm (#12) screw in a set of four will carry 10kg (~22 lbs.) without issue, assuming that you're in solid anchoring. Plastic plugs of the correct size should do well, or wood if you're precise.

I would actually consider using stainless steel machine-thread screws with hex heads. They'll look nicer and allow you to rotate the head to get some degree of adjustment with respect to out-of-level conditions. You could also slip smooth bushings over the protruding portion of the threads to clean up the appearance, and you could place small silicone bumpers on the top surface to reduce rattle and/or make additional height adjustments.

Run the screws in at least 30mm (~1-1/4") and only leave them extending about 20mm (~3/4"), to reduce torque load. 

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To increase precision when drilling, level accurately and start with a small drill bit. Select a location that's not troublesome, such as at the center of a brick.

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