You might try looking for a finger pull router bit. Some are available with enlarged diameters and flat bottoms. I'm working on an almost identical project and I've had to machine an extended shank for a Craftsman carbide bit that uses an adapter type arbor. The door was white pine laminated with fir which appeared to be solid fir. Louisiana rain made quick work of rotting it out.Does anyone know where I could buy an inverted cove bit with a quarter inch radius and no bearing guide on the fat end. It would be okay if there was a bearing guide on the shank end. I need to cut the following profile see picture. The profile on the top has a quarter inch radius. Profile on the bottom as an eighth of an inch on the roundover part. If there isn't such a router bits anyone have a recommendation for a hand tool I could use. This is part of reconstructing an old door.