Historically used in the construction of masts and booms for wooden boats, the birdsmouth joint is straightforward to make, stronger than a traditional mitre and with nested joints, easier to glue up without shifting.
With these three cutters, it is a simple matter to make 6, 8, 12 or 16 sided hollow columns, as well as straight or tapered multi-sided planters, bowls, etc., all of which can be left multi-faceted or planed/sanded round. Generally, more sections are required for larger-diameter assemblies to keep the wall thickness to a minimum, and reduce the amount of material to be removed when rounding.
Designed to produce flush joints with material up to 22.2mm thick. Thicker material can be used, but will require some dressing after glue-up.
For better safety, these bits should be used only in a router table equipped with a fence and not used free hand.