I have been asked to bid a double entry door with a 3'3" radius arch. I have made interior doors, but not arched. I plan to do a glue-up of 1/8" strips or use Kerfkore for the arched top of the jamb. What is the best way to attach the arch jamb to the legs (or vertical sections or the jambs)? Any suggestions, pictures or drawings would be greatly appreciated.
(Architectural Woodworking Forum)
From contributor J:
Laminate the arch from solid wood strips and leave a few inches of straight legs (past the tangent point). Butt-joint the arch to the lower legs using a couple of dowels and a countertop connecting bolt in the back. The laminated door-stop should lap beyond the butt-joint.
Anyway, we laminate the header from 1/8" veneers. We use a radius rf press, but used to use a male and female form and cold press them. Two parts, one for your jamb thickness (most architects spec 3/4"), and one for your filler (most all are 1/2"). The filler is then ripped to the spec'd width but left long and a 1/8" x 1/2" rabbet is routed around the edge. This will be the weatherstripping kerf.
Then we laminate the two together. We use a box joint where they meet at the springline, but if you don't have a CNC machine this could be pretty time consuming. I recommend it anyway, as you could do a decent job on the bandsaw or a perfect one on the router table, depending on how much time you want to spend. I've never used dowels, but they would be a quick method. We use Titebond 2 both in rf and while cold pressing. The pressures vary for species, and our library of tweaked programs that account for springback is vast, based on thousands of door and window jambs laminated over the years.
As far as joining to the legs I miter the head joint and rabbet away the stop and carry the integral stop of the legs into the head rabbet. Stainless screws and good glue have always worked better than trying to dowel such a joint. The real trick is creating a jig that counters the stress of the glue up so the resulting radius head has net zero tension before joining. Make the door after the jamb if you don't feel confident in your jig.