As others have said, 1/4" is plenty thick for Robart hinges. Again, use the Robart drill guide for accurate centering. The trick to staying centered is to drill slowly and to hold a finger on either side of the surface being drilled. You will be able to feel the bit through the wood if you start straying off center, then you can correct for it.

Make some practice holes in a piece of scrap balsa. You'll be surprised by how well you can tell where the bit is going and how well you can correct it.

Dave