Please advise a newbie about rail and stile router bits
Please help a newbie by recommending the correct router bit shape. Here's some background about the project. Mom has several doors in her house that rotted. It seems that whoever assembled the doors did not paint the edges of the door slabs, and the doors did not hold up to the weather on the gulf coast. Most of the doors that have the problem are fixed French patio doors. They do not move but look exactly like the few doors that do move. For this reason, we feel the they can be repaired without too much worry since these fixed doors will not swing at all.
These painted exterior doors are 30 years old and were made by a company that is no longer in business. Each door has thin rails and stiles with one double glass pane. We've repaired a couple of doors just by using 8/4 fir boards to replace the rotted bottom and top rails. While dowels have been sufficient, we would really prefer to find a router bit with 1/2" shank to make the nice grooves that the original doors had in addition to dowels. The photo shows the door slab viewed from the top so you can see the joint (highlighted by the blue box) between the rail and stile.
We can't seem to find the same bit that the door manufacturer used. We're new at this and don't know which other styles of bits can be used. Can anyone tell which router bit is acceptable for joining rails and stiles of this thickness? Would it be a finger-joint bit? Is there instead a rail and stile bit for this wood thickness (1.75" actual thickness)? Now that you see the joint between the rail and stile, do you think the dowels are enough and perhaps the groove is unnecessary?