Beech ply warping

[Philip Florio]

I bought some 4X8 sheets of beech plywood.

My first use in using these 3/4" sheets is a box for sandpaper. 1 1/2 weeks ago I cut the pieces and yesterday I went ahead to cut the dado for the shelves. What I found before cutting the dado is the sides which are 13" X15" cupped, the middle cupped inward.

My next project is more important, I plan on building a router table enclosure. Could I be doing something wrong?

Phil

[Steve Jenkins]

How were the pieces stored? If they were laying flat on a bench it is probably due to humidity changes. If you are going to leave them flat they should be stacked and covered so you don't get uneven air circulation on both faces.

[Howard Acheson]

If you cut multiple dados across a panel in most plywood and do not almost immediately fill them with something, the plywood will cup toward the dados. By cutting some of the veneer plies you have upset the balance of the multiple layers of veneer and the slightest amount of moisture in the air will cause the warping.

The answer is to either within a few hours glue whatever you intend to go into the dados or sticker them across the dados and put a significant weight on top.

[Philip Florio]

I noticed the warping before cutting the dadoes.

When I cut the pieces I laid them horizontally on the table with the hardboard shelves.
I guess when I make the enclosure for the router table I'll cut right before.

Phil