Shaving the Coves
Next comes the coving operation. Replace your dado blade with a sharp, full-kerf combination blade for this ask; a thin-kerf blade is too flexible for coving. If you’ve never cut coves before, it’s actually a shaving process in which you’ll run your workpieces at an angle across the blade, raising the blade about 1/16″ with each pass. Two scrap fences form a “tunnel” to keep the rails and stiles on track and at the correct angle of approach. Here’s how to set it up: With the blade raised to 3/4″, clamp the front fence exactly 2-7⁄16″ ahead of where the blade teeth drop into the table. Arrange this fence so it also crosses the saw table diagonally at 50.5°. Lower the blade. Install the rear fence 3-3⁄4″ behind the front fence and parallel to it. This fence should be at least 1-1⁄4″ thick, because you’ll gradually bury the blade into it as the cut advances.
Now, you’re ready to begin shaving the cove. Raise the blade to about 1/16″ for the first pass. Orient your workpieces so the edge closest to the groove is against the front fence. Use a push pad and push stick to feed the wood across the blade. Then, continue raising the blade a little more each time until you’ve sawn the full cove. Carry out this entire operation first on test scrap to make sure you’ve got things dialed in correctly, then repeat with the rails and stiles. Pretty cool technique, isn’t it?
When the dust settles, remove the coving fences, and reset the rip fence to cut the little bevel adjacent to the groove. Tilt your blade to 35.5° for these cuts. Then, it’s back to a wide dado blade, nested partially in a sacrificial facing clamped to your rip fence, to cut the rabbet that will hold the frame’s contents. Raise the dado blade 1/2″, and project it 1/4″ out from the fence to mill these rabbets.
That wraps up the shaping process for the rails and stiles. Before you assemble them, now is a good time to give the parts a thorough sanding or scraping while the surfaces are easy to reach.