Make Pencil Marks 6 Inches Apart for Perpendicular or T-Joints
For perpendicular joints, such as in the construction of bookshelves where the edge of one board is fastened to the face of another, hold the boards to be joined together and make pencil marks on both boards to indicate where the biscuit cuts should be made. Space the cuts about 6" apart. Place the two boards parallel on top of each other, with the top of the horizontal board aligned with the line you just drew. Clamp the two boards together in this position.