No, I am not trying to seal in any chemical vapors. The entire sheet
has some type of very hard and slippery material (melanminre? ) top and
bootom. I want to seal the machined area to minimize material
fragmentation due to use. The recess I machined was a perfect fit for
my router lifter, and I anticipated that within several hundred hours
of operation that the metal (anodized aluminum) to MDF junction would
become sloppy from vibration if I did not seal the MDF. However, since
I never worked with MDF before, I was curious if the small region that
is sealed would swell, thus making my now perfect fit, not perfect. As
I type this I am thinking that even the polyurethane may erode after
hours of vibration so maybe I'll just go with the untreated recess and
see when if it needs any attention in the future.
By the way, the router lifter does have leveling and tensioning
adjustments, but the recess is sized perfectly for height, with a minor
amount of "slop" for lateral adjustments.