With finger joints, it's not about the bit, it's about the jig.

Building a well-adjusted BJ jig is very fussy. The alternative is using a DT
jig with a BJ template (you might as well buy the stock).

I have had good luck end-joining painted exterior trim with but joint,
biscuit joined and water-resitant glue. Over a hal-dozed years the latex
paint has kept a continuous skin over the joint.

If you have access to a buiscuit joiner, I'd go that way, otherwise a more
traditional scarf.

A BJ is labor intensive if you're not set up for it and it would look just
plain weird when it telegraphed through the paint.


For the curious, I'm replacing some of the trim boards on my house
that have rotted at the end(s) because no caulk was applied when
installed 15 years ago

I'll take end-priming before caulk any day,

-Steve