Hello,
Phenolic resin inserts are fine, actually. They are dimensionally very stable, flat and have good wear resistance. Better wear resistance than aluminium actually, unless it has been hard anodised. I would say the standard 3/8 thick phenolic is less flexible than 6 mm ally too. The trick is to make the opening in the table only as large as necessary to allow the router base to fit.
I would say aluminium plate is OK too, but how do you cut the opening and make inserts to fit so we can accommodate different sizes cutters? Not easy unless you have the means. Phenolic ones come with a selection of inserts. Home made phenolic ones can be done easily with woodworking tools i.e. a router!
Incidentally, my homemade table has a 3 mm phenolic top, so I lose no height adjustment on the router. It is as flat as a fluke, because the sub table is substantial and supports the phenolic top right up to the router base. I make my own inserts to accommodate cutters from 2 mm to 80 mm wide and everything in between, and I can drill pepper pot dust extraction holes in them, too.
Mike.
