Is there a free tolerance for riveted structural parts?

Hello, I work as a riveter. I don't dare to say how much I know, but I can have more than ten years of riveting work experience to your questions, I hope to help you, you can learn from it.

The tolerances of riveting and welding parts are quite wide, unlike lathes, milling machines, and planers. We generally have plus or minus 2 to 3 mm there. The diagonal requirements are higher, but they are plus or minus 2 mm – no less than 2 mm for small and no more than 2 mm for large.

Note: The tolerances of riveting and welding parts are flexible, and I don't want to be so rigid as lathes and milling machines, because riveting and welding parts are basically assembled into mechanical parts with bolts at the end, so it can be simply said - "as long as you can put on the screws" (this is the words of our workshop workers). Also, when our riveters dry riveting and welding parts, they will also deal with the tolerances according to how the riveting and welding parts are used, for example, the tolerances of some riveting and welding parts are larger and better, not small, and our riveters will do it bigger; If the tolerance of the riveting and welding parts is small and good, but not large, our riveters will do it small.

This is also due to the flexible tolerances of riveting and weldments.

Hope it helps!

It depends on the accuracy requirements of the parts, and the general weldment does not have high requirements for length, so it is not necessary

2±..3 are all possible.

Limit deviation values for linear dimensions of free tolerances Tolerance class Size segments >3 6 >6 30 >30 120 >120 400 >400 1000 >1000 2000 >2000 4000 f (precision) m (medium) 2 c (rough) 2 3 4 v (coarse) -1 4 6 8 Table 2 Limit deviation values of rounding radius and chamfer height dimensions Tolerance class Size segment >3 6 > 6 30 >30 F (precision) 1 2 m (medium) C (rough) 1 2 4 V (coarseest grade) Table 3: Limit deviation values for angular dimensions Tolerance class Length segments 10 > 10 50 > 50 120 > 120 400 > 400 F (precision grade) 1° 30' ±20' ±10' ±5'M (Medium) C (Rough) 1°30' ±1° ±30' ±15' ±10'v (coarseest grade) 3° 2° 1° 30' ±20'The length of the angular dimension is determined by the length of the short side of the angle, and for the conical angle, it is determined by the length of the cone.

gb/t 1804-2000 gb/t 1184-1996

National standards for dimensional tolerances not indicated.

In the old national standard (HG) 159-59, the accuracy level was divided into 12 levels in terms of the tolerance of reference parts. Taken from one of the two levels of precision datum tolerances, known as free dimensional tolerances. Divide the deviations into; There are two types: one-way (+) or (-) two-way ( ).

In accordance with the national standard 1804-2000 (stipulates: the general tolerance is divided into 4 tolerance grades: precision F, medium M, rough C, and coarse V. The limit deviation values for each tolerance class are given according to the linear and angular dimensions of the unmarked tolerances.

The free tolerance is that there is no specific requirement for the tolerance range when the drawing is issued, that is, the tolerance is not required when the dimension is marked.

Free tolerance generally refers to the size that is not marked on the drawing, and the national standard has specific provisions for free tolerance. However, for skilled technicians or old workers, it is rare to see the national standard in actual work, because it is almost written down, and even if there is an error with the national standard, it has no effect, because the ancient name means that it is a free tolerance. The free tolerances are not marked with tolerances, and the dimensional requirements are --- obvious.

The larger the size, the greater the free tolerance value.

According to the basic size, the company's drawing template will have a free tolerance to be marked. <>

In mechanical drawing, the tolerance of the size without the tolerance was called the free tolerance in the past, but now this name has been abolished, and it should be called "the tolerance of the size without the tolerance", see the national standard "GB-T1804-2000 General Tolerance, Tolerance of Linear and Angular Dimensions without Tolerance".

The dimensions that are not marked are free tolerances, and the state has regulations GBT 1840--2000, which stipulates the general tolerance grades and limit deviation values of line types and angular dimensions that are not marked with tolerances. It is suitable for metal cutting and general stamping.

The dimensions of non-metallic materials and other process processing methods can be used as a reference.

For example: What is the free tolerance for size 32! Linear Dimensions》30 120 Limit Deviation F (Precision Grade) M (Medium Grade) C (Rough Grade) V (Coarse Grade).

The free tolerance is the unmarked dimensional tolerance in the standard, and the parameters are shown in the figure.

Free tolerance, due to the different nature of the products processed by each factory, the standards implemented by each factory are not the same, the standards implemented by agricultural machinery are lower, and the internal combustion engines, instruments, etc. are implemented higher.

We use tolerance class 9 as the free tolerance.

The unnoted tolerance grade of machining is specified as IT12 to IT18 grade, and the difference is generally used for holes, -difference for shafts, and other linear dimensions.

The linear dimensional free tolerance classes are divided into Precision Class F, Medium Class M, Rough Class C and Coarse Class V.

Combined with the GB T1804 national standard, and then select the level (precision, medium, rough, coarse) according to the implementation requirements, and there are many medium-level applications.

Check the national standard, it seems to be IT12 level, there is a mechanical manual.

Depending on the specific situation, resistance welding controls the dimensional tolerance compared to fusion welding, because of its high degree of mechanization; It is used in precision instruments and high-end cars, and the dimensional tolerance requirements are high; Ordinary automobiles and pressure vessels have slightly lower requirements for dimensional tolerances, and you can refer to GB19804 welding structure dimensions and geometric tolerances.

It depends on the accuracy requirements of the parts, and the general weldment does not have high requirements for length, so it is not necessary

2±..3 are all possible.