Some routers use a proprietary guide system, while other manufacturers
provide adapters or design their base plates to accept commonly
available aftermarket guides. To determine whether a particular
router accepts aftermarket guides, look at the hole in the
base plate. If it has a 1-3/16" through-hole with a 1-3/8"
diameter counterbore, it does.
Usually, guides are sold in a set that includes different
sizes, but often you can find individually sold ones. Standard
aftermarket guides include a ring nut that secures the guide
to the base. Some specialty aftermarket base plates allow
the use of standard guides with routers having original bases
that use a proprietary system.
Guides are especially useful in a low-production environment
where you are making a number of the same pieces. Creating
a template for trimming a rough-cut piece of wood ensures
that each piece will be identical to all the others. However,
the templates themselves must to be thick enough to accommodate
the depth of the guide. Remember this when planning your project,
as different manufacturers and even different guide diameters
can come in varying depths. Also, be sure to firmly attach
the templates to your stock using double-sided tape or even
screws if one side of your finished project won't show. You
can also use clamps if they don't get in the way of the router.
You can use guides with a fixed-base router, but using a
plunge router is more effective for routing internal cavities
or shapes. This allows you to properly position the router
first, and then plunge the bit into the wood.