How to determine drawer weight capacity?

Question

I am fitting my pantry with custom drawers, and I am worrying a bit about the weight capacity of one drawer in particular. The drawers are 14" wide and 21" deep. I've constructed them with the front/back and sides made with 1/2" baltic birch plywood - plus a prettier drawer front, but that's not really relevant. The bottom is 1/4" birch veneer plywood, dadoed and glued in on all four sides. The boxes were assembled with pocket screws to join the front/back to side pieces, and supported with full length side-mount drawer slides.

I think this should be able to handle most pantry storage needs for this size of drawer ... but the drawer I'm worrying about is the bottom one that will hold lots of bottles. According to the online Sagulator, a shelf of those dimensions made of "fir plywood" should be able to handle 50 pounds of uniformly-distributed weight no problem (and that's not accounting for the dado support on the front of the drawer) - with 'fixed ends'. With 'free ends' not so much.

It's sort of hard ... I find all kinds of guidance about what is "normal" or "light duty" versus "heavy duty" for drawer construction, but no quantitative indication of how much weight that really means, even approximately.

Is the Sagulator a reasonable way to figure out drawer weight capacity? Does a glued dado count as 'fixed ends'?. (The dadoes are not super snug, unfortunately ... not super loose but not as snug as I would have preferred). For me specifically, would this drawer construction (and size) support a drawer-full of bottles, I'm estimating maybe 30 pounds or so?

p.s. the 1/4" plywood has a description of "White or Yellow Birch Grade B2 (or equivalent) with a veneer core CARB Phase 2 compliant" for the inner plys, if that matters.

Answer 1

Is the Sagulator a reasonable way to figure out drawer weight capacity?

No.

Does a glued dado count as 'fixed ends'?.

If you glue in yes, but the dados front and back change things completely.

You can't extrapolate from a shelf to a drawer bottom, unless you build the drawer bottom essentially the same as a shelf, which of course is rarely if ever the case and isn't the case here. There's no useful way in the Sagulator to account for the bottom being held both front and back¹. And this is even assuming you're looking at data for the same material......

Their data is for fir plywood, softwood plywood, and you're using hardwood plywood. This isn't quite the same as going by the numbers for white pine when you're building using oak, but it's close ^_^

I'm estimating maybe 30 pounds or so?

TBH I was expecting an estimated load far more than this so it was quite a surprise when I finally got to this number! Even if you'd said 30 kilos (2.2 times more) I'd think you could be OK.

However this is just a judgement call, a guess. If you need some better confirmation in advance of completion I would go to one or more of the woodworking fora that has members who do drawers commercially and get their read on this².

If you'd prefer to proceed immediately and want to err on the side of caution there are a few things you can do:

• go with 1/2" material for the bottom;

• glue strips (slips), preferably in solid hardwood, along all four edges;

• add a muntin strip done the centre.

If you don't have any 1/2" ply on hand you can simply glue two pieces of 1/4" together, but be sure to lightly sand the mating surfaces before glue application, don't skimp on glue, spread it evenly, and ensure good clamping pressure in the middle by some means.

For the slips, I was initially thinking adding them on the underside only but given the shape of bottles you'd lose no useful storage space adding them inside the drawer as well (these ones, or all of them, can be quarter-round if you like).

While muntins generally divide a drawer bottom you definitely add some useful strength even having one mounted underneath.

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¹ Although it is some equivalent of the edging strip how to quantify it?

² My suspicion is you'll get a range of responses from "try it and see" to "remake with a thicker bottom", along with some saying this'll be fine.