PS

You might prefer to get a router guide that follows a template laid
over the work:
http://www.diydata.com/tool/router/guide.jpg

The follower will need to run in a hole marginally larger than the one
the cutter is making -by the difference in the size of the follower and
the diameter of the bit.

E.g.:

If the bit is 1/8" smaller than the guide, the template has to be 2 x
1/8" larger or 1/8" larger for each edge cut. The followers come in as
many varieties of sizes as the bits do. Just make sure the bit isn't
too large for the one you buy.