What are the usual steps to carve out a non-90degree mortise that will be married to a sliding wedge/key? Should the wedge be cut first?
When chiseling a usual mortise, plumb can be used as the reference. In tusk-tenons, the angle is generally kept low to prevent the wedge to slip out -- but much lower than the bevels on most chisels.
I've thought of different options to guide the carving, from a pilot drill hole, to a workpiece jig (that allows the chisel to be held plumb), or an angled guide block (against which the chisel can slide up and down), to altering the walls of a square mortise with a rasp. Can it be simpler than that?
Examples of angled mortises:
There are ways to avoid the angled wall, but they're not what I'm looking for:
In the second image (Moravian bench), it would be possible to use a router to make space in the center of the laminated tenon. Like an inlay plane.
Update: I've found video material online which describes one way to cut these mortises, and included links in this answer.