Subject

Tool chosen depends on the size of the scarf.

I've use both a router and a power plane, each with it's own jig to make
a lot of scarfs on pieces less than about 6" wide.

If sheet goods are involved, then the Gougeon Bros have a neat
attachment for a circular saw.

I would do most anything to avoid a belt sander, they are strictly a
PITA except as an abrasive stock removal tool, IMHO.

Lew