On Saturday, July 30, 2016 at 11:01:02 AM UTC-7, dadiOH wrote:
"DerbyDad03" wrote in message
...

Why are there so many different sized bushings?

There are only two times I've used bushings:

1. When using a router to make shelf pin holes.

2. When I need to follow a curved surface.

For making sliding-dovetail slots, one requires a guide jig.
So, cobble something up quickly, and make the guide slot with your dado
set on the table saw...
but, that slot won't be wide enough to guide a router base, so unless
you have dovetail bits with guide bearings (I don't), just use the bushings.
Centering doesn't matter, here, if you don't rotate the router during
the cut.