I have to ask if it really matters if the groove ends in a true taper. Why not use your router and core box bit, or better, router table and cut the groove stopping it just short of the end of the arm. Wouldn't that work just as well ?
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I have to ask if it really matters if the groove ends in a true taper. Why not use your router and core box bit, or better, router table and cut the groove stopping it just short of the end of the arm. Wouldn't that work just as well ?
Before you spend time trimming to width and shaping the top, cut the groove. It's easier to work with an oversized piece.
I’m assuming the groove tapers up just so,it isn’t seen on the end. If that is true (and it is being painted) then I’d be tempted to just route the grove through and then glue in a short piece of mating dowel on the end then trim to fit and paint.
What is the total length of the piece? Maybe I can figure out the correct angle of the slope and the starting pint.
A table saw with molding head will create that effect, sort of like the large diameter shaper cutter. The only new source I'm aware of is Corob Cutters, I don't know that the Craftsman head is still sold. Corob sells a 1/2" & 3/4" flute molding knives if those will work.
Are you going into production making these armrest pieces? You only need to make two of these things at most, right? And you have a short deadline. Use the core box bit and get it close. Then finish the shaping by hand. It'll be close enough and it's on the underside where it won't be seen when it is installed. Even if you run the core box bit slightly long, it won't matter. Just don't come out the end. Do you have the chair in your shop so you can try the fit?