2.2. View, cuts, and hatching

Information on technical drawings

Types of technical drawings: Technical drawings are often used for communication between departments, or between customer and company.

According to their tasks, manufactuirng and assembly have different demands regarding technical drawings. This is why technical drawings are often differentiated in manufacturing drawings, assembly drawings and explosion drawings.

• The manufacturing drawing contains a model with measurements for manufacturing. It is necessary to display every detail of the model by using different views, sections and cuts for complete dimensioning (refer chapter "2.3 Dimensioning of technical drawings)

• In contrast, an assembly drawing shows how different parts can be assembled to a module. If the assembly drawing is forwarded to a customer, it should also contain information on component connections (refer chapter "2.4 Component connections). An assembly drawing should contain every used part at least once in any view, which is often only achieved by using sections or breakouts. A parts list is usually included with an assembly drawing. The parts list is a chart that lists all models within the respective group, including position number and quantity.

• The explosion drawing is used as help for assembly or is preferably used in replacement part catalogues.

---

Display method: According to DIN ISO 128-3, there are two different methods for projecting views. Their symbol is placed in the frame of the drawing. These methods differ in terms of the projected views' orientations in relation to the main view. Different view directions and different orientation for side views are the result. The usual method for display in Germany and most european counties is projection method 1. Method 3 is usually applied in the USA. This CAD course exclusively uses method 1. Projection method 3 will not be explained further.

Symbols for projection methods:

Projection method 1

The follwing example illustrates projection method 1. 3D-CAD-Systems often include an option that only permits correct projection relative to the base view. The arrows on the 3D model represent the view direction of the respective side view. To explain this example: Seitenansicht von rechts means that the respective view was projected by rotating the body relative to the base view (so to the left - left side).

---

Views and sections: In technical drawings, the 3D-model is displayed by projected views. The most important rule for doing so is:

"You should only show as much views as necessary for completely describing the geometry of a model."

The base view should always be the most descriptive view of a model (or assembly). In manufacturing drawings, the actual orientation of the model in manufacturing is preferred as base view.

---

Section types: The ball head of a lever is cut in 3 different ways to illustrate the different types of sections:

Stepped section: It is practical to divert from half or complete sections when you need to display features that are not located within the section plane. In this case you can create a custom path to cut along. This is why a stepped section can contain more information than a complete or half section. The section path is indicated by a wide dotted and dashed line. The arrows on the ends of the line indicate the direction of view. The section and the respective section view is named with uppercase letters (A,B,C, etc.). Sections can be placed at will, usually along the longitudinal axis or perpendicular to it.

The following example illustrates a stepped section through a bench vice. The section through the middle of the vice offsets down to reveal the screw connection of the jaw, which would otherwise not be located in the section plane.

Rules for sections: You have to make sure to exclude certain parts when using sections.

The following models should not be sectioned (refer DIN ISO 128-3):

Rotating parts like shafts (except sockets and shafts with complex inner contour), axes, cones, bolts and standardized parts (e.g. pins, screws, rivets, nuts, washers, ...)

This exception only applies when the symmetry line of these parts is located within the drawing plane.

Parts used for connections (feather keys and wedges) should only not be cut along their longitudinal axis.

---

Displaying details:

For clear display, details are displayed in a scaled view. 

Connections of parts on shafts or screw connections are examples for details that are displayed too small in base or side views.

You should use the latter letters of the alphabet to avoid confusion with section views.

The following example shows a detail of the bench vice from before. The ball head is pressed on a bolt. In order to be able to create this fit along the whole surface, an undercut has to be added. This ensures tight fit of the ball head on the bolt. The undercut is now displayed enlarged, to be able to determine the type of undercut and add dimensions later on.

---

Hatching according to DIN ISO 128-3 and 128-50: Especially when cutting assemblies, make sure that each part has its own hatching that makes the part recognizable in each view. As a rule, the basic hatching is used. Care should be taken to use different hatching directions for different parts. In certain applications, a material-specific hatching can also be used.

The angle of the crosshatch should always be defined relatively to the main contour or symmetry lines (refer following example:)

The following rules apply when using hatching:

• The space between hatching lines should be adjusted to part size. Very narrow sections can be displayd completely in black.

• If you cut multiple parts touching each other, their hatching's angles should alternate between 45° and 135° and the distance between hatching lines should differ.

• A breakout section that is not located in the section plane is marked by a slightly offset hatching.

---

Standardized scales according to DIN ISO 5455:

---