In engineering practice we see many objects having curved surfaces or edges. Every curve has a name and property which defines it.

Point is the basic identity in a drawing. All curves are obtained by the path traced by a point while moving in a constrained motion.

Most commonly used curves in engineering practice are

1. Conic Sections: – These are the curves obtained on having sections of a right circular cone by a plane from different positions relative to the axis of cone. Circle, Ellipse, Parabola and Hyperbola are the curves defined by conic sections.

2. Cycloidal Curves :- These are the curves obtained by the path traced by a fixed point on the circumference of a circle, which rolls on another circle or time without slipping. The circle rolling on another circle or line is termed as generating circle while the circle or line on which it is rolling are termed as directing circle or line. Cycloid, Trochoid, Epicycloid, Hypocycloid, Epitrochoid and Hypotrochoid are the types of cycloidal curves.

3. Involute :- Involute is the curve traced out by the end point of a string unwound from a circle or polygon. String is kept tight so that it will remain tangent to the circle or co-linear to the side of polygon.

4. Spiral :- It is the curve traced by the point moving continuously along the line and at the same time line is rotating about its one end.

5. Helix :- Helix is a curve traced by a point moving uniformly around the surface and at the same time along axis of a cone or cylinder.