Crazy Wood Movment Question

[Hammer5573]

I had some leftover purple heart and some maple so I decided to have a go at making an end grain chessboard. I cut the pieces 1.5” x 1.5” and 5/8” thick and glued them to a piece of 3/4” plywood as a backer for rigidity. I sanded it using my drum sander until it was flat.Last week I noticed that the underside (plywood) was raised in the middle. I drum sanded it until it was flat. I looked at it today and noticed that the opposite (chessboard) side is now raised by approximately 1/4”? Any ideas what is happening here?

[Chet]

Plywood is laminated in an uneven number of layers, this is what keeps it stable.  My guess is when you glued your chessboard pieces to one side you made it an even number of laminations making it unstable.  So when gluing to ply, you need to do something to both sides.

[Von]

On 4/1/2024 at 1:21 PM, Hammer5573 said:

 I cut the pieces 1.5” x 1.5” and 5/8” thick and glued them to a piece of 3/4” plywood as a backer for rigidity. 

I haven't done this myself, but 5/8" is pretty thick for the pieces since that is almost as thick as the plywood and hence could be exerting a lot of force on it. I believe I normally see the pieces cut much thinner.

[Hammer5573]

On 4/1/2024 at 1:59 PM, Chet said:

  My guess is when you glued your chessboard pieces to one side you made it an even number of laminations making it unstable. 

Would this explain movement in both directions?

[wtnhighlander]

Yes, it most likely warped like a Pringles chip, resulting in humps on both sides, but probably opposite diagonal directions.

[Barron]

I wouldn’t try laminating anything thicker than 1/8” or maybe 3/16”. It would take a very long time to thin the top down to a reasonable thickness, maybe a belt sander with really coarse grit, then use the drum sander to o finish it off. Good luck. 

[Hammer5573]

On 4/1/2024 at 8:05 PM, wtnhighlander said:

Yes, it most likely warped like a Pringles chip, resulting in humps on both sides, but probably opposite diagonal directions.

No…it is definitely raised in the middle.