A router is going to be about the fastest. Drilling will take way to
long. Just make a u shaped channel that you can drop the posts into on
top of a table. Plunge and route. You can use a small level to draw a
line across one end of the post, then it is easy to rotate it 180
degrees and do the cuts from eaither side. Just mark the channel where
you want the cuts. You could even build stops for real accuracy.

On Aug 11, 5:29*am, Wood Guy wrote:
A friend wants to build a fence using round, 6" diam cedar posts and 1"
x 6" pine or spruce boards.

He wants to cut slots through the center of the posts (3 slots) that are
just large enough to slide the boards through. *There are going to be
lots of posts - maybe 100 or more.

How would you go about forming these slots? *What sort of tool?