What causes wood to warp?

I've heard and seen that moisture causes different layers of wood to expand at different rates, and thus the wood warps. But it seems that if you dry the wood back out it doesn't un-warp, usually it cracks.
Here's why I wonder: I'm working on a small end table with my wife. We bought a sheet of layered (don't know what you REAL wood workers call it) oak and maple. We've gotten quite a ways into the project, but this sheet, which is for the table top, has significant warp. Probally close to 1/4" in some dimensions. So I'm wondering how to unwarp that so we can secure it to the frame of the table.
The ideas we've had to date: (1) Right now, so it doesn't warp more we have clamped it to scraps of oak that run across. (2) There's a lot of different clamps out there. Since the plan calls for a railing to run around the edges of the top, we are thinking that we can just clamp it to the railing. This may not take out all the warp, but it will warp with the railing. Better in some ways. [The railing will be pegged to the top. And the top will be pegged to the frame. No visible fasteners, right?.] (3) I've read quite a few post about planing the top. I'm not too wild about that since, the top layer of oak isn't thick enough so that all the warp could be planed out. I suppose we could plane the bottom, but it seems like a bad idea to plane through the laminate layers.
Suggestions? I'm very new to wood working, so I'm very open to ideas, comments, and suggestions.
Emil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If it's a plywood top, then yes, just attach it down to the frame to straighten it out. you could screw it in from the bottom (no one is going to see the screws on the underside of a side table).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Oh boy. First off, NEVER plane plywood. It will do unspeakable things to your planer and ruin the wood. The veneer (top layer of oak or maple) is probably only about 1/32" thick anyway. Try cutting it roughly to the size you need and placing it on a flat surface, then either clamping it down flat with some straight boards or placing some weights on it and leave it alone for a few days. If that doesn't work, report back, we'll get ya going in another direction. --dave

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks! That's the path we're on, and it seems to be working. Thanks again! Emil
wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.