Flexible drafting curves have been a staple in the draftsman's tool chest for many years. It is used to draft curves accurately so that the draftsman is not limited by his ruler and triangles. Some curves come lined with a built-in ruler so that the curve can be measured. Others have no measurements and are flat on the bottom to keep the curve stable. Most curves are made of a rubber material to prevent slipping while drafting. Ultimately, the goal of a drafting curve is to be able to draw curves that do not conform to pre-determined drafting curves such as the French curve template.
Setting Up a Drawing
Tape the paper down to the table using your drafting tape. This will ensure accurate measurements and prevent slippage.
Sharpen your drafting lead to a drawing point with which you are comfortable.
Ensure that there are no obstructions in your drawing area. This is important especially when using expensive drafting mediums, such as vellum or mylar, that can easily be damaged by close objects.
Using the Drafting Curve
Mark any two points on your paper using your drafting leads.
Place one edge of your curve touching one point and the same edge further down the curve touching the other point. Notice that there is a natural curve to the drafting curve no matter where the two points of contact. The drafting curve automatically creates a two-dimensional arc, whose apex is equidistant to the two points.
Draw two different points that are closer together than the original two.
Use your drafting curve to repeat the same process of drawing a natural curve between the two points. Notice that the arc is less flat and steeper than the original arc you drew in the step above. You will also notice that the same is true about this new arc in that the midpoint is equidistant to the two points.
If you have a drafting curve with ruler integers on it, mark the two starting points at exact points on the ruler. Then, measure and mark the midpoint using the ruler to confirm how the drafting curve works.