hi,

you're really looking for trouble here. I would definately not spend
the time making the top as it stands now. There are a few things you
could do:
1) if the maple was under 6 inches square then you might get away with
it. make sure when you finish it to seal it well (ie don't just use
an oil or wax finish)
2) use a floating panel, but then of course the top will not be flush
3) run the grain of all the walnut in the same direction (you'd have
to do a 20" glueup of course, but that's not really a problem), check
that the expansion factors of your maple and walnut are similar
otherwise your joints will still bust
4) make the maple panel out of four right-angled triangles glued
together (their right angles in the center of the tabletop)
5) use a maple veneer over an mdf (or whatever) backing.

I like (4) and (5) much better than (1), (2) or (3). (4) could look
quite good but it really depends on your taste.

A

-- 
apprentice neanderthal #42
homepage: http://www.physics.adelaide.edu.au/cgi-pschulz/andy-cgi/andyhome
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