Grain Direction of Plywood

[Coop]

As I was putting the last coats of Arm-R-Seal on 12 ea. 31" x 16" drawers for the wife's craft room, I noticed that I had run the grain for one of the drawer bottoms different than the other eleven. The drawers are constructed of 1/2" Baltic birch w/ fully captured 1/4" birch ply bottoms. I assumed that for the greatest strength for the bottoms, that the grain should run the shortest direction, which is front to back. Not that these will hold anything that is super heavy, but just wondering what is the correct direction to run the grain? 

[Eric.]

When it's ply it doesn't matter since it has the same strength in any direction.  For solid bottom drawers I'll sometimes run the grain across the drawer so it can expand out the back...if I build the drawer that way.  Otherwise I just orient the grain in the most aesthetically pleasing way, which is usually with the grain running with the longest dimension. 

[Coop]

Well I shot my theory down when I took my pocket knife and separated the micro thin veneer from the next ply to find that the first real ply runs against the veneer grain, so on a 1/4' sheet, there are 2 plys that run the width of the sheet and 1 (the center) runs the length. The same holds true w/ 1/2" and 3/4". I also found that on construction grade, just the opposite, as there is no veneer, the first ply runs the length of the sheet. I obviously had too much time on my hands last night

[Eric.]

If sagging is that much of a concern that you're analyzing plies, I might just use 1/2" next time.

[Coop]

I probably should have just gone and gotten a beer instead of splitting plys and over analyzing it

[wtnhighlander]

I would say your drawer bottoms will be fine. But on lower grade ply having only 5 layers, there are only 2 layers opposing the grain direction of the faces. In that case, there is a distinct difference in strength across the face grain vs. with the grain.

Don't ask how I know....