Assembly of the Floor Joist...

With the glue in the channel's, It is time to mate the rails to the spline. Due to a snug fit, a rubber mallet is employed to tap everything into place. It is important to be gentle with the spline as to not mess up the edge. Start the spline with your hands, then follow with the mallet after both rails are started on the spline.

This is the time to make sure all the ends are square and flush with each other before proceeding to the next step.