1. Calera High School STEM
Freehand Sketching
Calera High School
STEM

2. The Importance of Sketching
The process of sketching promotes spatial thinking, visualization, and logical, systemic ways of creating geometry.
It should be thought as a convenient method for quickly expressing and communicating ideas graphically.

3. Sketching Technique
Technical sketching is done freehand and rapidly; not with a strait edge and drawning instruments.
When creating a sketch, do not tape the paper down. Instead leave it free so that it can be turned to a convenient angel for sketching.
Straight lines are normally sketched by first marking the endpoints of the line.

4. Sketching Technique
Horizontal lines are typically sketched from left to right.
Vertical lines are best sketched with a downward, pulling motion.
To sketch curved lines for arcs, cylinders, and rounded shapes, first, draw lines to indicate the center of the curve.

5. Model Building
Although faster more accurate than manual drawing methods, 2D CAD has the same limitation as the drawing board. It is two-dimensional. As a tool for visualizing and creating objects that may be viewed from their front, top, right side, auxiliary, or isometric positions, 3D CAD offers more power than 2D CAD.

6. Movable Construction Planes in 3D
All 3D CAD programs provide the user with a virtual “3D space” in which to construct models. In order to use this modeling space accurately and efficiently, the user must have some method of controlling the position and size of every 3D object in space. This is accomplished with the Cartesian coordinate system containing X, Y, and Z axes.

7. Movable Construction Planes in 3D
A moveable local coordinate system called the user coordinate system (UCS) is supplied to the user.
The local UCS can be repositioned on-the fly by the user, similar to a tape measure, and placed anywhere and at any orientation within the modeling space

8. Movable Construction Planes in 3D
A construction plane (also referred to as a work plane or a reference plane) can be thought of as an infinitely large 2D drawing plane that can be positioned anywhere in 3D space.

9. Modeling Primitives
There are currently three distinctively different methods used for geometric modeling in 3D CAD programs; wireframe, surface, and solid models.

10. Boolean Operations
Boolean operations allow the user to perform three types of operations; union, difference, and intersection.
The union operation, is essentially an additive operation with all selected primitives being merged into a new single composite object.

11. Boolean Operations
The difference operation is a subtractive operation that creates a composite solid subtracting the overlapping volume of one set of primitives from another set of primitives.
The intersection operation takes only the overlapping 3D volume common to all selected primitives and makes that common space the resulting object.