1. General Concept of Tolerance
1.1. General tolerance refers to the tolerance that can be guaranteed under normal workshop conditions. For dimensions with general tolerances, it is not necessary to write down their limit deviation values after the dimension. Instead, it should be explained in the drawing, technical requirements, or technical documents (such as business standards), etc.
1.2. General tolerances can be applied to geometric elements such as linear dimensions, angular dimensions, shape and position.
2. Tolerance degrees and limit deviation values for metal cutting machined parts and stamped parts (excerpt from GB/T 1804-2000)
2.1. Table of tolerance degrees and limit deviation values
Table 1 – Limit deviation values for linear dimensions (mm)
| Tolerance degrees: | Basic Dimension Segmentation | |||||||
| 0.5-3 | >3-6 | >6-30 | >30-120 | >120-400 | >400-1000 | >1000-2000 | >2000-4000 | |
| Precision | ±0.05 | ±0.05 | ±0.1 | ±0.15 | ±0.2 | ±0.3 | ±0.5 | – |
| Medium m | ±0.1 | ±0.1 | ±0.2 | ±0.3 | ±0.5 | ±0.8 | ±1.2 | ±2 |
| Rough c | ±0.2 | ±0.3 | ±0.5 | ±0.8 | ±1.2 | ±2 | ±3 | ±4 |
| Coarser v | – | ±0.5 | ±1 | ±1.5 | ±2.5 | ±4 | ±6 | ±8 |
Table 2 – Limit deviation values for fillet radii and chamfer height dimensions (mm)
| Tolerance degrees: | Basic Dimension Segmentation | |||
| 0.5-3 | >3-6 | >6-30 | >30 | |
| Precision | ±0.2 | ±0.5 | ±1 | ±2 |
| Medium m | ||||
| Rough c | ±0.4 | ±1 | ±2 | ±4 |
| Coarser v | ||||
Table 3 – Limit Deviation Values for Angular Dimensions (mm)
| Tolerance degrees: | Basic Dimension Segmentation | ||||
| -10 | >10-50 | >50-120 | >120-400 | >400 | |
| Precision | ±1° | ±30′ | ±20′ | ±10′ | ±5′ |
| Medium m | |||||
| Rough c | ±1°30′ | ±1° | ±30′ | ±15′ | ±10′ |
| Coarser v | ±3° | ±2° | ±1° | ±30′ | ±20′ |
2.2. Notation style: For example, when selecting the middle degree, it should be marked as GB/T 1804-m. Our company generally selects the level m and does not need to be marked. Other levels of precision must be marked on the drawing.
3. General size tolerance and positional tolerance for welded structures (excerpt from GB/T 19804-2005)
3.1. Length dimensions.
The limit deviation values for length dimensions listed in Table 4 are applicable to the length dimensions of welded parts and welded components, such as external dimensions, internal dimensions, pitch dimensions, width dimensions and center distance, etc. Our company generally selects Grade A and does not need to be marked. Other levels of precision must be marked on the drawing.
Table 4 – Linear Dimension Tolerances (mm)
| Degree of tolerance | Nominal Dimension | ||||||||||
| 2-30 | >30-120 | >120-400 | >400-1000 | >1000-2000 | >2000-4000 | >4000-8000 | >8000-12000 | >12,000-16,000 | >16,000-20,000 | >20,000 | |
| A | ±1 | ±1 | ±1 | ±2 | ±3 | ±4 | ±5 | ±6 | ±7 | ±8 | ±9 |
| B | ±2 | ±2 | ±3 | ±4 | ±6 | ±8 | ±10 | ±12 | ±14 | ±16 | |
| W | ±3 | ±4 | ±6 | ±8 | ±11 | ±14 | ±18 | ±21 | ±24 | ±27 | |
| D | ±4 | ±7 | ±9 | ±12 | ±16 | ±21 | ±27 | ±32 | ±36 | ±40 | |
3.2. Angular Dimension Tolerance
The limiting angle deviation is as per Table 5. The nominal dimension of the angle deviation is based on the short edge as the reference edge, and its length is calculated from the reference point indicated in the drawing, as shown in Figure 1 to Figure 5.
If the angle is not noted on the drawing, but only the length dimension is noted, the allowable deviation should be in mm/m.
Our company generally selects Grade A and does not need to be marked. Other levels of precision must be marked on the drawing.
Table 5 – Angular Dimension Tolerance
| Degree of tolerance | Nominal Dimension | |||||
| 0-400 | >400-1000 | >1000 | 0-400 | >400-1000 | >1000 | |
| Tolerance expressed in angle Δα（°） |
Tolerance expressed in length (mm/m) |
|||||
| A | ±20′ | ±15′ | ±10′ | ±6 | ±4.5 | ±3 |
| B | ±45′ | ±30′ | ±20′ | ±13 | ±9 | ±6 |
| W | ±1° | ±45′ | ±30′ | ±18 | ±13 | ±9 |
| D | ±1°30′ | ±1°15′ | ±1° | ±26 | ±22 | ±18 |
3.3. Positional tolerances of welded components.
The tolerance of straightness, flatness and parallelism not marked on the welded component must be in accordance with the provisions of Table 6. Our company generally selects Grade E and does not need to be marked on the drawing. For the other levels, they must be marked on the drawing.
Table 6 – Tolerance for Relinearity, Flatness and Parallelism (mm)
| Degree of tolerance | Nominal Dimension (corresponding to the longest side of the surface) | |||||||||
| >30-120 | >120-400 | >400-1000 | >1000-2000 | >2000-4000 | >4000-8000 | >8000-12000 | >12,000-16,000 | >16,000-20,000 | >20,000 | |
| AND | ±0.5 | ±1 | ±1.5 | ±2 | ±3 | ±4 | ±5 | ±6 | ±7 | ±8 |
| F | ±1 | ±1.5 | ±3 | ±4.5 | ±6 | ±8 | ±10 | ±12 | ±14 | ±16 |
| G | ±1.5 | ±3 | ±5.5 | ±9 | ±11 | ±16 | ±20 | ±22 | ±25 | ±25 |
| H | ±2.5 | ±5 | ±9 | ±14 | ±18 | ±26 | ±32 | ±36 | ±40 | ±40 |
3.4. The selection of dimensional and positional tolerance degrees for welded components is shown in Table 7.
Table 7
| Degree of precision | Scope of application | |
| Linear Dimension | Positional Tolerance | |
| A | AND | Welded components with high dimensional accuracy requirements and importance. |
| B | F | Relatively important structures produced in batches with small thermal deformations caused by welding and straightening. |
| W | G | General structures such as box structures with large thermal deformation caused by welding and straightening. |
| D | H | Structural components that allow greater deviations. |
4. Dimensional Tolerance for Castings (taken from GB/T 6414-1999)
4.1. The dimensional tolerance for castings specified in this standard refers to the tolerance that must be achieved under normal production conditions.
4.2. The numerical values of dimensional tolerances for castings must comply with the provisions of Table 8; the degree of tolerance will be selected in accordance with the provisions of Table 9.
Table 8 – Numerical Values of Dimensional Tolerances for Castings (mm)
| Blank castingBasic dimension | Degree of tolerance TC |
|||||||||||
| > | ≤ | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 10 | 0.36 | 0.52 | 0.74 | 1 | 1.5 | two | 2.8 | 4.2 | ||||
| 10 | 16 | 0.38 | 0.54 | 0.78 | 1.1 | 1.6 | 2.2 | 3 | 4.4 | |||
| 16 | 25 | 0.42 | 0.58 | 0.82 | 1.2 | 1.7 | 2.4 | 3.2 | 4.6 | 6 | 8 | 10 |
| 25 | 40 | 0.46 | 0.64 | 0.9 | 1.3 | 1.8 | 2.6 | 3.6 | 5 | 7 | 9 | 11 |
| 40 | 63 | 0.5 | 0.7 | 1 | 1.4 | two | 2.8 | 4 | 5.6 | 8 | 10 | 12 |
| 63 | 100 | 0.56 | 0.78 | 1.1 | 1.6 | 2.2 | 3.2 | 4.4 | 6 | 9 | 11 | 14 |
| 100 | 160 | 0.62 | 0.88 | 1.2 | 1.8 | 2.5 | 3.6 | 5 | 7 | 10 | 12 | 16 |
| 160 | 250 | 0.7 | 1 | 1.4 | two | 2.8 | 4 | 5.6 | 8 | 11 | 14 | 18 |
| 250 | 400 | 0.78 | 1.1 | 1.6 | 2.2 | 3.2 | 4.4 | 6.2 | 9 | 12 | 16 | 20 |
| 400 | 630 | 0.9 | 1.2 | 1.8 | 2.6 | 3.6 | 5 | 7 | 10 | 14 | 18 | 22 |
| 630 | 1000 | 1 | 1.4 | two | 2.8 | 4 | 6 | 8 | 11 | 16 | 20 | 25 |
| 1000 | 1600 | 1.6 | 2.2 | 3.2 | 4.6 | 7 | 9 | 13 | 18 | 23 | 29 | |
| 1600 | 2500 | 3.6 | 3.8 | 5.4 | 8 | 10 | 15 | 21 | 26 | 33 | ||
| 2500 | 4000 | 4 | 6.2 | 9 | 12 | 17 | 24 | 30 | 38 | |||
| 4000 | 6300 | 7 | 10 | 14 | 20 | 28 | 35 | 40 | ||||
| 6300 | 10,000 | 11 | 16 | 23 | 32 | 40 | 50 | |||||
Observation:
① The basic dimensions of the casting refer to the dimensions indicated on the drawing and must include machining tolerances and draft angles.
② For castings with basic dimensions less than or equal to 16 mm, CT12 tolerance values are selected for grades CT13 to CT15.
Table 9 CT Casting Dimension Tolerance Classes
| Batch and mass production. | Production of small batches and unique pieces. | ||
| Manufacturing methods: | Degree of tolerance | Impression material | Degree of tolerance |
| Manual sand casting | 11~13 | Dry and wet sand | 13~15 |
| Sand Casting and Shell Molding Machine | 8~10 | Self-Hardening Sand | 11~13 |
| Metal casting | 7~9 | ||
| Low pressure casting | 7~9 | ||
| Investment Casting | 5~7 | ||
4.3. The tolerance zone must have a symmetrical distribution, that is, half of the tolerance must be positive and the other half negative.
However, in special requirements an asymmetrical configuration may also be used, which must be indicated in the drawing or technical document.
The degree of casting tolerance must be indicated in the relevant drawing or technical document. If not specified, all castings will be made to grade CT11.
