I make a lot of paint-grade raised-panel doors, using poplar frames and ultra-light MDF panels, glued into the frame. I have a new cope-and-stick shaper set with a 3/8" profile. A current project requires solid maple raised panels. Do most of you rely just on the cope-and-stick joint, or reinforce the joint? In the past, especially on bigger doors, I would reinforce the cope-and-stick with a floating tenon done on my horizontal mortiser. More recently I've done the same with the portable Festool Domino. Most of the doors are fairly small (12 x 24), and I plan to make the rails 3" wide for a little extra glue surface. What do the big door makers like Conestoga and Keystone do?
From contributor S:
For us it depends on the thickness of the rails and how many mid rails. I do not think I have ever made a raised panel door taller than 40" without a mid rail, they just look funny. The mid rail adds a lot of strength, especially if it is wider than two inches. For shaker style doors with thinner flat panels we use lighter plywood and wider frames so again the frame is stronger due to the wider cope joints.
There have been times where I add dowels to the cope (we have dowel machines so this is the obvious choice for us) but it is usually due to odd engineering issues like heavy door mounted hardware or excessively wide doors. For tall raised panel doors with no mid rail I would want to add dowels. It is easy to do and only takes a minute to do. I do not have any great engineering parameters for deciding this it is based on experience. I also would not glue in the panel on a large door, even if it is MDF.