Technical Drawing: Projections, Sections, and Views
Overview and Sections
Cuts
A cut is the artifice by which, in the representation of a piece, we remove some of it to clarify and make the representation and annotation easier.
Section is the shear plane intersection with the part (the area indicated in red). When representing a section, unlike a cut, we do not represent the rest of the piece left behind. Whenever possible, we prefer to represent the section since it is a clearer and simpler representation.
Cuts are standard devices that we use imaginatively in pieces where interpretation is difficult. It is impossible to show their hidden or interior areas to clarify the interpreter. The cut is a representation showing the interior parts of the body. The surface seen in the shear plane is called the cut surface.
The operations to be applied to implement a cut are:
- Determine the shear plane, which must be parallel to the plane of projection.
- The surfaces cut or sectioned must be clearly identified and should therefore be drawn by Norma striped. These lines indicate the area being cut or severed and make it stand out. This streak of court is known as chitterlings, and the representation varies according to the type of material used.
The following is an example of some of the most commonly used materials:
Classification of Cuts
Consider that there are three basic types of cuts:
- Cuts as the principal axes
- Cut Total
- Cuts off-axis
- Cuts staggered
- Cut the Fourth
- Special Courts
Projections
The graphic projection drawing is a technique used to represent an object on a surface. The figure is obtained by using auxiliary lines projecting that, starting from a point called the focus, reflect that object in a plane, like a shadow. It is also the representation by projecting the observer that affects a plane. It can be:
- Cone (central or perspective)
- Parallel
Diédrico System
In the case of the dihedral system, the lines projecting are perpendicular (orthogonal) to the projection plane. In this system, unlike others, we do not get a volumetric representation of the object in perspective but its elevation, plan, and profile. From these views, you can get a three-dimensional representation of the object in the axonometric system, projecting lines which can be both orthogonal and oblique, with the cavalier perspective a particular case of this system.
The Dimensioned Drawing
A variant of the dihedral, the dimensioned drawing, is also an orthogonal projection, namely the representation of insurgents or more parallel sections of the object. This system is used for better definition and reproduction of complex surfaces, such as sections of a building, the hull of a ship, the terrain profile, and similar items that, in practice, cannot be adequately described by the above-identified systems. They are widely used in architecture, engineering, surveying, etc.
Octagonal Projection
Octagonal projection is one whose projecting auxiliary lines are perpendicular to the plane of projection, establishing a relationship between all points of the projected projecting element.
Isometric Projection
An isometric projection is a graphical method of representation, more specifically an axonometric [1] cylindrical [2] orthogonal. [3] It is a visual representation of a three-dimensional object in two dimensions, in which the three main orthogonal axes, as designed, make angles of 120 degrees, and the dimensions parallel to the axes are measured in the same scale.
Isometry is a form of projection used in engineering drawing that has the advantage of allowing the representation to scale and the disadvantage of not reflecting the apparent decrease in size-proportional to the distance-as perceived by the human eye.
Conventional Projections
Conventional projections are those that do not follow a real projection system. An example is the Polycentric projection, which is adopted by the National Map of Spain. Here we assume the peninsula divided by meridians, with a distance between them of 20′ in length, and parallel, with 10′ of difference between each of them, forming a grid. These curvilinear trapezoids represent the entire national area and are numbered. To perform the screening itself, we plot in the center of each trapezoid plane tangent to the ellipsoid so that the earth is replaced by a polyhedral surface circumscribed. Since every polyhedron is a small surface, we assume that it matches the curvilinear trapezoid. With this method, the maximum anamorphosis is on the corner of the trapeze, which at 1:50,000 scale, which is used, is negligible.
Projection of Elements
Projection of a Point
A point in space is represented by its two projections (as a shadow) on the principal planes: horizontal projection and vertical projection.
Projection of a Line
A line is defined when they meet their two projections, horizontal and vertical. Projecting a line onto a plane is another line formed by the projection of all points of it. Knowing the pairs of projections of two points on a line, the projection is obtained by joining them.
Projection of a Plane
A plane is defined by its two traces: vertical and horizontal. The traces of a plane are the lines of intersection with the principal planes (PV and HW). A line belongs to a plane if the vertical line is drawn on the vertical plane, and also, the horizontal trace of the line is drawn on the horizontal plane.
Isometric View
The isometric view is based on a rotated grid, given a fixed elevation, which gives a diamond shape to the grid as shown below. This provides a representation in three dimensions but no prospect of an object or several and is particularly suitable for engineering models.