A short course on marking curves
Draw a curve
Most woodworking projects rely on straight lines and right angles, but sometimes you need a nicely formed curve to give your project a more stylish look. So how do you make a curve when you're modifying a project plan or designing a piece from scratch? Study the curved shapes in good furniture to develop your eye. Then try the techniques shown here.
When you're tinkering with a curve, trying to get it just so, draw on a full-size piece of plywood, medium-density fiberboard, cardboard, or paper instead of putting it directly on your stock. You can tape together brown paper bags from the grocery store to make a template as large as necessary. Transfer the curve to the workpiece by cutting out the template and tracing along its edge.
For symmetrical shapes with multiple curves, draw exactly half of the shape on plywood, hardboard, or paper. Cut out that piece and use it as the template for the other half.
Remember that you already own an array of templates for simple shapes. For example, anything from a five-gallon bucket to a small washer can serve as the pattern when you need a round corner. And once you've made a nice template, save it. Put it in a drawer, or hang it on perforated hardboard, because you just might need it again someday.
Big curves are simple with a trammel
A simple radius, like those found on some Shaker furniture, calls for nothing more complicated than a wooden trammel and a pencil. Without a measured radius from a plan or a computer-aided drawing, however, it does take some guesswork. Establish the width at each end of the pattern, then experiment with different lengths for the trammel until you have a good-looking curve. Make the trammel handier to use by drilling several holes along its length for different radii. Place the pivot end on a scrap piece equal in thickness to your pattern piece, as shown in the photo at the top of this page.
Here's a neat way to draw an ellipse for tabletops, trays, and the like. Use a square to mark intersecting perpendicular lines on pattern material, such as a piece of medium-density fiberboard. Place pushpins on the long axis, equal distances from the centerpoint. Tie a piece of string into a loop, put it around the pins, and place a pencil inside the loop. Keep the string taut as you move the pencil clockwise or counterclockwise, and you'll draw an ellipse. Adjust the position of the pins and the length of the loop to vary the size and proportions of the figure.
The curved edge of this shelf bracket consists of three 1" radii. It's an example of a seemingly complicated design that you can draw quickly with a compass. To make such a pattern, decide on its length and width, then use those boundaries to locate point A for the center of each curve. Set the compass to the desired radius, place its pivot point on each mark and draw the curves.
You probably ran into a French curve at some point in school, but maybe you forgot all about it. This is a reminder that it can come in handy for designing furniture and other woodworking projects. The simplest application of this plastic tool is to draw a corner that isn't a radius, as shown here. If you'll need to repeat the shape, put masking tape on the French curve to mark the beginning and ending points. You can buy a set of four French curves, covering a wide variety of shapes.
Rely on a flexible curve to create the exact shape you have in mind, as shown here, or use it to transfer curves from plans or existing pieces. A plastic surface encloses a lead core, which holds almost any shape.
If you need to duplicate this curve on the other half of a workpiece, cut out the pattern with your bandsaw. Trace the pattern at one end of the workpiece, flip the pattern over, and trace the other end, as shown in the inset.