Working in circles is considered a waste of time, but you'd be surprised how often you really need to. In fact, there's been a lot of time wasted by people who couldn't figure out how to cut a good, clean circle (or arc) when they needed one.
To cut a circic with the router, the basic need is to get the router to move smoothly around a given point. You'll find that there are numerous way's to accomplish that and that each of the ways has advantages in certain applications. Almost always, you'll use a trammel of one sort or another. Occasionally, a template will guide the router.
But what about curves that aren't circles? Ovals. Arcs. Combinations of arcs. Here again, the router will do the work. To cut ovals, you use a special trammel. For those arcs and combinations of arcs, you are often best served by a template.
The most common way to cut circles or arcs with the router is to use a trammel. Your router may have one among its accessories. Usually, the trammel will be a pan of the edge guide attachment.
If you don't have one, it's easy to cut out an oversized plywood baseplate, mounting the router on one end and driving a nail for a pivot at the other. You can accomplish the same thing with a lot more flexibility by attaching a hardwood arm to the base and setting the pivot point in a sliding block on that arm. Infinite adjustment—almost.
Cutting circles is the natural turf of die plunge router. The plunger makes it easy to get the bit into the work and to deepen the cut after each lap. But plunge routers tend to be pretty beefy, too much so for a lot of trammel work, in my estimation. Don t get me wrong. I have routed a lot cf circles with plunge routers. But I'm inclined to use a small machine rather than the 3-horsc behemoths.
What I really like to use is a laminate trimmer, which you can hold in one hand. The hitch, of course, is that with the lam trimmer, as with any fixed-base router, you stand a good chancc of gouging the work trying to tip the bit into it. So you do have to practice. But it can be done. Manageability is a big plus in this kind of operation. With one hand on the pivot and the other on the router, you can make the cut quickly and accurately.
And if you arc worried about a lam trimmer being down on power, just remember: It doesn't take 3 horses to spin a '/»-inch bit.
Of coursc. this whole discussion may be academic for you. You may be in the same boat as one of my colleagues, Jeff Day. who says. "I only have one router, so it doesn't take a lot of thought which one I'm going to use."
In any case, with a trammel,you drive a pivot nail into the workpiece, Better yet. drill a pilot for the nail. A drilled pilot will ensure that the pivot is pcrdendicular. And by boring clean through the stock, you can use the same centcrpoint on either side. I would recommend working both sides. That is, use the router and trammel to groove one side, cutting about halfway through the stock. Then (lip the piece over and make a cut. Then keep going until you are through. You get a better finish on all the edges, and you don't have to cut so deeply.
The trimmer trammel is a simple cutout. It can be cut from acrylic, hardboard, or thin plywood. The
trammel in Trimmer Trammel was made for a Ryobi tilt-base trimmer.
To make such a trammel for your bminate trimmer, remove the baseplate. Trace the plate on cardboard, then draw an extension for the pivot holes. Cut out the pattern and attach it to your stock with double-sided carpet tape, then cut it to shape and drill the necessary holes.
This is the perfect device for making wheels for wooden toys. Oh, I know you can buy wheels cheap, but using them is like assembling a model. If I'm making a toy, I like to make the whole toy.
When making toy wheels, by the way. experiment with groove-forming bits. You can scoop out the wheel disk with a round-nose bit. then chamfer the edge with a V-groover, then complete the wheel by cutting it free with a straight bit. (Just don't use too big a bit in the trimmer; its low-horsepower motor may be overtaxed and succumb.) And you don't have to limit yourself to wheels for toys. How about wheeled furniture—the son of stuff you'd have on a deck or patio?
For those large arcs and circles— tabletops come immediately to mind—you do need a bigger trammel. The plywood teardrop shown below is more than 3 feet long overall, so with it you can rout a 3-foot-radius arc (that's a 6-foot-diametcr circle). With its reinforced edges, this trammel also doubles as jig for rabbeting assembled cases. (See the chapter "Rabbeting.")
Here's the quick and dirty approach to making this jig. Cut a rectangle of Winch plywood as wide as your router's base and about 6 inchcs longer than the radius of the arc or circle you want to cut. Use your router's baseplate to lay out the trammel's head with mounting-screw holes and a bit hole. Measure, mark, and drill the pivot hole you need. Attach the base to the router, and you're in business.
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