the rail system for the cupholders was an enormous part of the project. i settled on cutting a groove into the apron of the table and making matching inserts that fit into it.
if i did it again today, i'd do something different or modify the design. in testing, these worked perfectly and had plenty of strength. but cutting the rebates accurately with enough clearance to fit, but not so much that the inserts flop around, was an absolute nightmare. you have to account for wood movement, too