could you use a portion of a stile and rail bit set, by removing the slotting cutter and replacing with a bearing (from the other cutter)?
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Rockler Round-Edge Matched Stile and Rail Router Bit Set - 1-5/8" Dia x 1" H x 1/2" Shank
Precision-machined to guarantee a perfect fitting cope and stick joint — every time! Unconditional guarantee.