expansion and contraction construction advice needed

[tombo]

I'm building a pine toy box atm and have an idea for the lid its about 1000mm wide and 450 deep, all the wood is 18mm thick. My idea is a perimeter 100mm wide mitred at the corners (not sure if i should biscuit the corners or make a spline joint). Then fill in the field with 6 pieces floating tongue and groove. Should i worry about the field expanding and blowing the lid apart? if so how much should it allow for.

Tom

 

[Les Mahon]

Tombo

Assuming you have the grain runing in the long direction, I would have thought 2mm all round would be more than enough expansion room. In fact that should be enough regardless which way the grain runs. The most important thing is that the timber is aclimatised as close as possible to the conditions of it's final resting place before you measure / assemble the unit.

HTH
Les