When building frame-and-panel doors, I make them extra strong by making the tenons long. Rather than chisel out the deep mortises, you can cut them on a tablesaw.

In the stile, center a 14 "-deep groove for the panel with your dado blade. Then, raise the tablesaw cutting depth up to 1". Measure the width of your tenon and clamp a stopblock to your tablesaw fence as shown at far right. Then, run the stile groove-side down over the dado blade to the stopblock.
—Erv Roberts, Des Moines, Iowa