jtpr wrote:
....
swelled beyond the clearance again, this time just in the middle. I
had left a hacksaw blade width between each of the boards when I built
it, which I was told was about right for movement in this kind of
wood.
....
Who told you that???

I couldn't find published actual data; there are a number of
classes/types that are commercially labelled as "meranti". From the
picture I'd gather yours is one of the red (as opposed to yellow/white)
species; what I did find indicates expansion is roughly on the order of
oak (which also being ring-porous makes a certain amount of sense I'd
guess).

Anyway, rule of thumb for oak would be about 1.5% or so for initially
kiln-dried stock; for a nominal 6" plank that would translate into
roughly 1/8" or 1/2" roughly for the 27".

From your description that seems too low, too.

Did you treat the ends before assembly to at least minimize wter absorption?

Other than either adding more spacing when dry or making the tolerances
on the closing side larger there's not much to do to stop its movement.

You could minimize it somewhat w/ finishing but even that won't stop it;
just slow it down some.
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