Meaning and detailed explanation
Technical drawing symbols - Surface symbols
Meaning of the surface symbols in the technical drawing
Surface symbols are used to standardize information about surface requirements on technical drawings. They are a central component in manufacturing and design, as they define the surface quality and the type of processing. The symbols ensure that the surface requirements of a component are interpreted in the same way worldwide, regardless of the location of the manufacturing plant.
The most important surface symbols and their application
The most important surface symbols and their meaning are explained in detail below. These symbols include basic symbols for general information, symbols for material-removing and non-material-removing processing and specific symbols for special surface requirements.
| Icon | Meaning |
|---|---|
 | Basic symbol should only be used if its meaning is explained by an additional word. |
 | Designation for a surface to be machined to remove material without further specification. |
 | Marking for a surface for which material-removing processing is not permitted. |
 | The longer side of the graphic symbols is given an additional line for special surface specifications. |
 | A circle is added to the graphic symbol if all surfaces of a part have the same surface quality. |
 | The specified surface finish can be achieved by any manufacturing process. |
 | The specified surface finish can be achieved by any method of material separation. |
 | The specified surface finish is achieved by any other process, but not by material separation. |
 | The specified surface finish is to be achieved by a special process, namely milling. |
 | Reference distance in mm for roughness measurement, not forRa and Rz specifications |
 | Groove direction of the predominant surface structure perpendicular to the groove direction. |
 | a - Roughness valueRa in µm after the abbreviationRa b - Manufacturing process, treatment or coating, other word specifications c - Waviness in µm after the corresponding abbreviation or reference distance in mm d - Groove direction f - Roughness values other than Rm in µm, with parameter abbreviation |
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1. basic symbol
The basic symbol is the basic symbol of the surface symbols and is often used as a starting point for further information. The basic symbol itself does not contain any specific information on the type of processing or the surface quality. It is mainly used when an additional word is required to specify the surface requirement.
Use:
The basic symbol should only be used on its own if the meaning of the surface condition is supplemented by an additional description in text form. It serves as a kind of "blank space" that only acquires its meaning through the additional information.
2. material-removing processing
This symbol indicates that the surface of a workpiece must be machined using a material-removing process. This means that material is removed from the surface by grinding, milling, turning or drilling in order to achieve the desired surface finish.
Labeling and meaning:
- Symbol without additional line: The symbol indicates that material-removing processing is required, but without specific details on the process.
- Symbol with additional line: If the longer side of the symbol has an additional line, this means that there are special requirements for the surface treatment. The process can be specified by a word, e.g. "milling".
Practical example:
In a technical drawing for a component that requires a smooth surface for bearings, this symbol could be used to indicate the need for a grinding process.
3. no material-removing processing permitted
This symbol indicates that no material may be removed from the surface. Surface treatment must be carried out using other processes such as polishing, coating or hardening, in which the material is not removed but only the structure is changed.
Labeling:
- Symbol without additional lines or symbols: This symbol indicates that all processes that do not involve material removal are permitted for processing.
Application:
This symbol can be used, for example, on components whose surfaces are to be given a certain structure, but without loss of material. Typical applications are galvanized surfaces that can be additionally polished or treated without removing material.
4. additional line on the longer leg
If there are special requirements for the surface finish, an additional line is added to the basic symbol. This line indicates that certain processes or processing methods must be used to achieve the surface quality.
Use:
The additional line indicates that special surface requirements apply that go beyond simple material-removing machining. A word specification such as "grinding" or "milling" can be added to indicate the specific method necessary to achieve the required surface quality.
Example:
This symbol could be used on a technical drawing for a high-precision component that is to be given a particularly smooth surface through specific processing such as CNC milling.
5th circle in the symbol: Same surface quality for all surfaces
A circle within the surface symbol indicates that the required surface quality should apply to all surfaces of a component. This marking simplifies the drawing by defining a uniform quality requirement for the entire workpiece.
Use:
The symbol with a circle is used when the entire surface of a component is to be processed evenly. All visible and accessible surfaces of the workpiece must have the same surface quality.
Application example:
A housing that needs to be uniformly coated or polished could display this symbol to ensure the same quality for all external and visible surfaces.
6. surface finish by any process
The symbol for a general surface finish indicates that the required surface quality can be achieved by any manufacturing process. It leaves open how the quality is achieved and is therefore more flexible in the choice of processing methods.
Use:
This symbol is used when the surface requirements are not linked to a specific process. However, the quality must meet the standards specified in the drawing.
7. surface treatment by any material-removing process
This symbol indicates that the required surface quality is to be achieved by any method of material removal. It therefore indicates that a process such as milling, grinding or turning should be used, without specifying the exact method.
Example of use:
This symbol can be used on components that are to have a certain roughness or surface structure, such as parts that will later be painted or coated.
8. surface treatment without material separation
This defines a surface quality that is not achieved by material separation processes. This can be achieved through coatings, surface treatments or special thermal processes.
Example of use:
This symbol may appear on components that are given a hardened or coated surface, such as stainless steel parts with a protective coating.
9. specific surface treatment (e.g. by milling)
For particularly demanding surfaces that have to be created using specific processes, the symbol indicates which process should be used with an additional line and text.
Application:
In technical drawings, for example, "milling" can be placed next to the symbol to emphasize the need for an exact milling process.
10. roughness and groove direction specifications
The roughness and the direction of the grooves on the surface are important parameters that further specify the quality of the surface.
Parameter for roughness:
- a: Roughness value Ra in micrometers (µm)
- b: Processing method or additional coating information
- c: Ripple in µm or reference distance for the measurement
- d: Groove direction of the surface structure
- f: Other roughness values like Rz, specified by abbreviation
Application:
These specifications provide detailed information on the surface finish and help to precisely fulfill the surface requirements.
FAQ: Frequently asked questions
- What is the meaning of the basic symbol without additional information?
- The basic symbol alone does not contain any specific information and is only used in conjunction with additional information.
- When is an additional line used in the symbol?
- An additional line indicates special surface requirements.
- What does a circle in the symbol mean?
- The circle shows that the entire surface of the component must have the same quality.