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4) Cutting circles of any size with an attachment you can make yourself, actually the circle's size is limited by the maximum diameter the attachment can be adjusted to. The base works like this: It acts like a pair of compasses, but instead of the pencil you have the router bit and in place of the point of the compasses there is a sliding, adjustable pivot pin in the base about which you rotate the router. The drawing illustrates this probably more clearly. The trick is in the sliding arrangement for the pivot pin. Mine is made up from a short piece of 5/16" (8mm) square bar with a fixed upper plate and a loose lower plate. The bar is tapped for the pinch screw that draws the plates together. The pin is fixed into the bar.
	With the experience gained in using the router you can cut the slot with recesses so the plates of the slider are flush with the base. The base is cut from 3/8" Lexan. The drawings convey the principle of the idea, use what is at hand to fashion an adjustable pivot. The first circle cutter I made up was merely a base fixed to the router, with the pin inserted into holes drilled at the right distance for the radius I wanted. In time of course you run out of places to drill new holes! As you probably guessed, to cut a circle you drill a center hole of the same diameter as the pin and pivot the router in it. It is as simple as that.
5) Trimming the centerboard slot with a flush cutting bit Finishing a centerboard slot after cutting it out with a jigsaw is another application for a router with a flush cutting bit. This is of course what the flush cutting bit is designed for, its most usual use being laminate trimming. In this instance we will use the bit to trim back the plywood bottom of the boat, flush with the inside of the centerboard case. The guide bearing of the bit runs along the cb case's inside. All we have to do is to add two runners to the base of the router to compensate for the slope of the hull bottom, otherwise the trimmed section will not be parallel to the case.
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