Best way to attach drawer bottoms: destructive test
But I have often seen the wood break where the groove is, and with the glue as strong as the wood, I was pretty sure that a glued flat on drawer would be stronger, because the wood isn't weakened by a groove.
The boxes with the bottom in a groove need to be assembled with the bottom in place.
My test setup consists of my screw jack on a bathroom scale, with a camera watching the scale. A "plunger" sits on top of the screw jack. The box is placed upside down on the plunger. The plunger pushes on the "bottom" of the box until it breaks.
Breaking the first box. I cranked the jack up to 300 pounds, which is the maximum that the scale will go to. But aside from some creaking of my apparatus, nothing happened. So I kept cranking until the scale read 150 again. With one and a half turns on the scale wheel, this indicated 450 pounds. Once at 450 pounds (200 kg), the reading didn't increase anymore. I figured this was because the box was starting to yield, so kept cranking. Eventually, the bottom flew off with a loud bang. The jack, and much of the apparatus jumped from the sudden release of force.
But then I saw the scale was quite bent. The jack was in the middle of the scale during the test, but bounced to the side when the force was released. The reason the force stopped increasing past 450 pounds was because the top of the scale had bent enough to make contact with the bottom part. So there was probably a lot more than 450 pounds of force.
I was surprised just how much force it took to break these boxes!
I still think under the right circumstances, the bottom glued on flat would be stronger. But at the same time, if I used lesser quality plywood, where the bond between the laminations is not as strong, no matter how strong my glue is, the plywood itself would just de-laminate to pull off the bottom. So for those cases, the rabbeted bottom would always be stronger.
Looking at the drawers for my tool stand, these are at least 4x the length and width. Which means it should take about 2400 pounds to pop the bottom of the drawer. 2400 pounds is 1.1 metric tons. But even if I filled the entire volume of the drawers with solid lead, that would only weigh about 200 kilograms. So there is a lot of safety margin.
In the mean time, the drawer slides on this cabinet are rated for just 25 kilograms (55 pounds). Also these particular drawer slides wrap around the bottom of the drawers, which would also help to hold the bottom on.
An advantage of putting the drawer bottom in a dado is that the drawer would not slide very well on a plywood bottom. But for these workbench drawers, I still glued the plywood flat on the bottom.
I actually used some painted scrap plywood. I scraped the paint on either edge and glued a strip of maple on. Maple is harder and slides better than spruce. That way I get a harder sliding surface and still get to glue the drawer bottoms flat on the bottom.
Pocket hole strength
tests (vs. other joints)
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