There are two basic tools for marking out circles and curves – compasses and dividers. Both can be used for most woodworking jobs rounding the ends of boards and cutting small holes, for example – but dividers cut through the surface fibres of the wood and so have an advantage when the curve or circle is to be seen later. Dividers also remain sharp. To avoid marking wood noticeably with the centre point, use the tools lightly. On plastic and other hard surfaces, glue a small piece of card where the center point will go. If necessary this can be removed afterwards.
For marking curves and circles which have radii larger than dividers and compasses can stretch to, you can make a simple beam compass from a length of wood, a bradawl and a scriber or pencil. To do this, bore a series of holes through a straight piece of hardwood, push the bradawl through a hole at one end and use this as a pivot. Push a pencil or scriber through one of the other holes and use this to mark the curve. A piece of string with a drawing pin attached to one end and a pencil or scriber to the other can also be used to mark out circles and curves.
Dinner plates, ashtrays, pennies and so on are also useful for marking circles.
A piece of string can also be used to mark out an ellipse. First draw a rectangle with dimensions the same as the major and minor axes of the ellipse you want to draw. Quarter the rectangle by drawing a horizontal line and a vertical line joining the mid points of opposite sides. Set a pair of dividers or compasses to half of the length of the rectangle. Place one point on the bottom of the vertical line quartering the rectangle and make two marks near opposite ends of the horizontal line. Fix a pin at each mark and attach a length of string between the pins so that the centre of the string just reaches the bottom of the vertical lines when it is taut. Place a pencil against the string and draw an ellipse by keeping the string taut all the time.
