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I am building wall-mounted shelves for my electronics lab. These will basically be pieces of MDF supported by Spur Steel-Lok uprights and brackets, similar to what the picture below shows.

I can figure out the load bearing capacity of the supports from Spur's literature.

But what about the MDF? Given the thickness and the depth of the material, as well as the weight of the expected load, how do I compute the maximum spacing between uprights?

P. S. In case this somehow matters, I am specifically looking at MF (Melamine Faced) MDF.

illustation

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  • woodbin.com/calcs/sagulator. The sagulator can help – Kris Jan 24 '19 at 21:14
  • @Kris: Thank you for that link. If you phrased it as an answer, I'd happy to upvote it! – NPE Jan 24 '19 at 22:26
  • Aside: You might want to consider mounting uprights closer together than the maximum allowable spacing. <US-centric> Installing them on every stud, typically 16" spacing </US-centric>, will allow you more flexibility in terms of using shorter shelves with erratic spacing to accommodate items of differing heights, depths, ... . Shallower shelves at head-banging heights can reduce discomfort. Using taller uprights (aka rails) allows more flexibility as well, e.g. a shallow low shelf to get meters and power supplies off the bench top and high shelves for rarely used items. – HABO Feb 14 at 16:39
  • Aside: There are shelving systems that use a horizontal rail from which uprights are hung, e.g. freedomRail. It makes it easier to put uprights where you want them regardless of framing. You can also add uprights to handle unexpected loads or specific items. – HABO Feb 14 at 16:48
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Pressed wood shelves should never span more than 32". Beyond that even their own weight will result in unsightly sag.

As for maximum load, you'll probably be unhappy with sag long before they collapse. For anything heaver than a row of paperback books, go every 16".

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  • Would you say these guidelines apply irrespectively of the thickness of the shelves (i.e. would 6mm and 25mm MDF have the same properties in this respect)? – NPE Jan 24 '19 at 22:21
  • Around here a person rarely encounters anything other than 3/4" (about 20mm) planks. It is that to which I refer. 6mm is absurdly thin. – isherwood Jan 25 '19 at 3:14
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It is difficult to give specific engineering for MDF as well as finger jointed material due to variables like humidity and potential for spill absorption. If you are maximizing the support spacing, I strongly recommend coated shelves or applying primer and paint yourself. enter image description here

According to https://www.nytimes.com/1987/02/08/nyregion/home-clinic-how-to-put-up-shelves-and-make-sure-they-re-level.html :

Supporting brackets for most shelves should be spaced no more than 24 inches apart for light to medium loads (15 to 20 pounds per foot). This means that the vertical slotted pilasters must be spaced at about that distance from one another on the wall. However, for heavier loads (30 to 40 pounds per foot), you will need brackets closer together to keep shelves from bowing, usually 16 to 18 inches apart, so pilasters will also have to be spaced closer together.

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  • Would you mind elaborating on how way coating would help? I am specifically looking at MF MDF, but it did not occur to me that a layer of melamine would matter. Or did I get the wrong end of the stick and you mean something else entirely? :) – NPE Jan 24 '19 at 22:23
  • This article gives great tips for working with MDF. While the face is hard, the inside is quite spongy. – John H Jan 25 '19 at 23:21

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