Often, a simple detail is all it takes to create a classic, traditional look in a project. Adding a thumbnail profile to the rails and stiles of a door frame is a good example. The result is a soft transition between the frame and the panel that draws attention in a subtle way.
Without a doubt, the profile shaped on the door frame complicates the joinery. The modern solution is to buy an expensive set of matching router bits for the job. However, I like to take a more traditional approach. This "hand-coped" technique, using both power and hand tools, produces a stronger joint that looks every bit as good as its router-made counterpart.
The technique really isn't difficult to master when you follow a simple routine. The step-by-step drawings shown here guide you through it. The end result is a seamless fit between the rails and stiles.
THE PROFILE. The first step is to cut the parts to final size from 3/4"-thick stock. Then you'll take them to the router table to form the profile on the inside edges, as in Figure 1. To do this, I use a 1/4" roundover bit set to a height of 5/16". You want to end up with a 1/16"-deep fillet or shoulder on the face.
__A GROOVE. __ Next, you'll cut grooves in the rails and stiles for the door panel. I like to do this with a slot cutter in the router table (Figure 2). You could use a standard blade rip blade or dado set in the table saw as well.
Note that the groove is not centered on the edge. The front shoulder falls right at the lower edge of the roundover profile - 5/16" from the face. And as you can see in the detail drawing, the depth of the groove matches the width of the thumbnail profile (1/4").
THE MORTISES. Now you're ready to lay out and cut the mortises in the stiles. Figure 3 shows how the groove acts as a guide for locating the mortises on the edges and sizing their width.
When laying out the length of the mortise keep a couple things in mind. First, remember to subtract the depth of the groove in the rails when figuring the length. And I always stop the mortise at least 3/8" from the end of the stile.
THE TENONS. The stiles can now be laid aside while you cut the tenons on the rails. This is probably the most challenging part of the joint.
If you take a look at Figure 4, you'll see that the tenon isn't centered on the thickness of the rail. This off-center alignment matches that of the grooves and mortises in the stiles. Furthermore, the front and back shoulders are offset. The shoulder offset should be identical to the width of the profile on the stiles - 1/4". In the finished joint, this allows the front shoulder of the tenon to mate with the shoulder line of the profile on the stiles.
When cutting the tenons, you can use the grooves as a guide to thickness and position them accurately. To get the shoulder offset right (1/4"), I compare careful shoulder-to-shoulder measurements along both the front and back of the rails. The difference should be exactly 1/2". Then once the cheeks and shoulders are cut, the tenon is completed by cutting the tenon haunch flush with the front shoulder (Figure 5).
FINAL FITTING. With the tenons completed, the joint can be partially assembled. However, the front shoulder of the tenon is blocked by the profile on the edge of the stile (Figure 6). It'll take a little more work on both the stile and the rail in order for the joint to close up.
First, you'll use a sharp chisel to remove a short section of the profile on the stile. This "waste" section should start about 1/32" short of the inside end of the mortise. Simply pare away the profile flush with the shoulder line and the bottom of the groove, as shown in Figure 7.
COPE THE RAILS. The final step is to shape or "cope" the end of the profile on the rail to fit over the remaining profile on the stile. This requires two operations.
To get a snug fit to the stile, you need a line to follow when coping the profile with a gouge. The trick here is to use a chisel and guide block (last drawing below) to miter the end of the profile at 45° (Figure 8). As you can see in the detail drawing, this miter cut creates a guide edge that's a match to the shape of the thumbnail profile on the stile.
The key to cutting the cope accurately, as illustrated in Figure 9, is to use a gouge with a sweep that's a close match to the radius of the profile. Start at the "short" end of the miter work back to the profile line with multiple light, chopping cuts. You want to "undercut" a bit at the tenon shoulder to ensure clearance over the end of the profile on the stile. When you get close to the profile line, you can test the joint. I shoot for a fit that's a tad tight and rely on gentle clamping pressure to close up the joint.
There are certainly faster ways to make a door frame. But when style and quality are your main goals, this technique rises to the top of the list. And the bonus is a large dose of "handcrafted" satisfaction.
