Warped Wooden Lamp Base - Why?

[city17]

Hi all, I'm trying to find out why the oak base of a small lamp has started to warp.

You can see the problem in the two images below, the wood warped and is pulling the glued on plastic down:

I have some theories why it started to warp, but I'm not sure which one is most likely, maybe someone here can help?

• The base is made from some old oak of unknown origin. I had it lying around and I think it originally belonged to the base of some machine, but it looked decent once I cut and planed it.
• I finished the oak with a mix of boiled linseed oil and wax (Kreidezeit Lappenwachs) on both sides.
• The top side of the oak is glued to the 3D printed lamp, so I have sanded it to remove the wax for better adhesion.
• The lamp uses a LED that doesn't really get too warm, you can easily touch it, but it does generate some heat from the top side.
• I've made a few more of these lamps, and they don't seem to have this issue (yet!), some of them are from different stock (quality recent white oak)
• Happened slowly over about 4 months

Is it due to heat from the top + one side having less finish? Or just tensions in the wood itself? Or some other reason?

 

[Argus]

Very often older pieces of wood, that appear stable in shape, will distort slightly after being reshaped or cut. Usually it is caused by internal stresses re-aligning themselves after residual moisture that remains is released.

You'll get this when re-sawing supposedly dry planks - very often the twist appears before you've finished the cut.

 

[thetyreman]

I think part of the problem with that is how one side will absorb more moisture than the other, perhaps a simple brace going cross grain will flatten it out and also allow air to circulate underneath, central heating can cause a lot of problems as well.

 

[TheTiddles]

Could be one or all of what you’ve mentioned. A thin piece like that being heated on one side, I’d expect it to be moving. Veneered ply would be an option that’s more stable
Aidan