You can predict the amount of movement
using our Wood Shrinkage Calculator at the
link included with my response.
If Gene Wengert weighs in, I suspect he'll
remind us all that the amount of wood
movement is based on species, the
change(s) in relative humidity, and the
"style" of the board (flatsawn Vs. 1/4 sawn). What
I've learned after many years of paying attention
to Gene's posts .... if the humidity in the
room the table will reside stays the same
(climate control), and the MC of the table/wood
when put in service matches the EMC of
the room, then there will be no movement.
Not a likely scenario - the EMC (equilibrium
moisture content) is a finite value - if you
know the relative humidity of a room, then you
can accurately predict the what the moisture content
of wood will acclimate to.
A short snippet from a WOODWEB Knowledge Base
article on EMC:
-----------
0% RH = 0% MC = 0% EMC
30% RH = 6% MC = 6% EMC
50% RH = 9% MC = 9% EMC
65% RH = 12% MC = 12% EMC
80% RH = 16% MC = 16% EMC
99% RH = 28% MC (approx.) = 28% EMC (approx.)
Note that most heated homes and offices will run 6% EMC
in the wintertime and even a bit lower. In the summertime,
9% EMC is common. Outside in most of North America,
the outside is 12% EMC, summer and winter. In coastal
locations, 16% EMC outside is common.
-----------
So - if you know what the RH swing will be where your
table will reside, you can use the calculator to predict
the amount of wood movement.
As mentioned be others, a steel-bound wood table slab
will likely be a problem. You don't mention a width,
but as an example, a 36" wide glued up wood slab
of flat sawn red maple (a relatively tame movement
species) will expand (or shrink) 5/16" cycling between
6% to 9% MC. If the table is 9% MC when put in service
in that scenario, it would shrink 5/16 - if it is
6% MC when put in service, it would expand 5/16.
Hope this helps, and if we're lucky, Gene will
confirm (or correct) my thoughts.
Carl