There are several types of fitting systems for bore shafts, which one is preferred, and why

Clearance fits, e.g. plain bearings.

Guide rail and slider generally refer to the moving pair that moves or rotates relatively; 2. Transition fit.

For example, gears and shafts, positioning pins and positioning holes, this kind of centering can be detached; 3. Interference fit.

For example, the hub of the turbine and the edge of the wheel are fixedly connected. Note that the fit of the hole shaft must be the same nominal size for bore. As for which fit to use, it is according to the requirements of the job.

The hole is machined well, the size does not change, whether you want to be loose or tight, by changing the size of the shaft (actually up and down deviation) to achieve, such a fit is called "base hole system" fit.

The shaft is machined well, the size does not change, whether you want to be loose or tight, by changing the size of the hole (actually up and down deviation) to achieve, such a fit is called "base shaft system" fit.

When the size of the hole is inconvenient to change, the base hole system is used; When the size of the shaft is inconvenient to change, the base shaft system is adopted; When it doesn't matter, the base hole system is used.

1. There are three types of fit when the hole is matched with the shaft, clearance fit and interference fit.

and transition mates.

2. Gap matching Yinshen: the size of the hole is greater than the size of the shaft;

3. Interference fit: the size of the hole is smaller than the size of the shaft;

4. Passing through the hall to fight and dress up to know the combination: the cooperation between the first two and the first.

5. In the basis of tolerance and measurement, the hole mainly refers to the inner surface of the cylindrical shape, and also includes the non-cylindrical inner surface (the inclusive surface formed by two parallel planes or facets). In mechanical principles and other disciplines, there are relatively perfect regulations on the size and deviation of holes.

1) Gap fit.

Mates that have clearances, including minimum clearances equal to zero, are called gap mates. At this point, the tolerance zone of the hole is above the tolerance zone of the shaft. The function of the gap is to store lubricating oil, compensate for various errors, etc., and its size affects the relative motion of the hole and shaft.

Scope of application: Clearance fit is mainly used for the active connection between holes and shafts, such as the connection between sliding bearings and shafts.

Since the actual size of the bore and shaft allows for variation within their respective tolerance zones, the clearance of the bore and shaft fit is also variable. When the hole is the maximum limit size and the shaft is the minimum limit size, the assembled hole and shaft are in the loosest fit state, which is called the maximum clearance xmax; When the hole is the minimum limit size and the shaft is the maximum limit size, the assembled hole and shaft are in the tightest fit state, which is called the minimum clearance xmin.

2) Interference fit.

A mate with an interference (including a minimum interference equal to zero) is called an interference fit. At this point, the tolerance zone of the hole is below the tolerance zone of the shaft. In the interference with the stove brigade, because the size of the shaft is larger than the size of the hole, it is necessary to use pressurization or thermal expansion and contraction methods for assembly.

Scope of application: interference fit is mainly used for fastening connections that do not allow relative movement between the bore concealment shafts, such as the connection between the gear ring and the hub of large gears.

In the interference fit, the difference between the maximum limit size of the hole and the minimum limit size of the shaft is the minimum interference ymin, which is the loosest state of the hole and shaft fit. The difference between the minimum limit size of the hole and the maximum limit size of the shaft is the maximum interference ymax, which is the tightest state of the fit between the hole and the shaft.

3) Transition fit.

The tolerance bands of the bore and shaft overlap each other and may have clearances or interference fits (which are generally small).

Scope of application: The transition fit is mainly used for positioning connections that require good alignment and coaxiality between the bore shafts and are easy to disassemble and assemble, such as the connection between the inner diameter of the rolling ballast motion bearing and the shaft.

The base shaft system is generally used in the following situations:

1. When the tolerance level of the fit is not high, cold-drawn steel can be used directly as the shaft. The dimensional tolerance of the cold drawn garden profile can reach IT7 IT9, the journal accuracy of a certain shaft parts, has been able to meet the performance requirements, under this condition, the base shaft system is adopted, the processing of the shaft can be avoided, and the holes can be processed according to the different fitting performance requirements, and the different properties of the fit can be obtained.

2. One axis is equipped with multiple holes, and the requirements for the nature of the fit are different.

3. In fitting, the shaft is a standard part. When using standard parts, the benchmark system cannot be used casually, but should be selected according to the regulations. For example, the rolling bearing is a standard part, and its inner ring and journal fit is a base hole system, while the outer ring and the empty fit of the shell should be a base shaft system.

When selecting the base shaft system, it should be considered comprehensively from the aspects of structure, process and economy, and weigh the pros and cons, mainly in accordance with the following principles:

1. Under normal circumstances, the base hole system is preferred in the design. It is more difficult to machine holes than shafts, and there are more tools and gauge sizes used. The base hole system can greatly reduce the specifications and quantities of customized knives and measuring tools.

2. In some cases, the base shaft system is used to match: when the parts are made of profiles with a certain level of accuracy that do not need to be processed with outer diameter, they are directly used as shafts; When assembling several parts with different properties on the shaft of the same basic size, the base shaft system should be selected for fitting; For holes or shafts that are matched with standard parts, the fitting system should be determined based on the standard parts.

For example, the fit between the outer ring of the rolling bearing and the bearing seat belongs to the base shaft fit; Another example is the fit between the dowel pin and the hole for the base shaft system.

3. Non-benchmark fit: Some fits in actual production, if there are sufficient reasons or special needs, non-benchmark fits are allowed, that is, non-benchmark holes and non-benchmark shaft fits.

Choice of base hole system.

In general, the base hole system should be preferred. In order to reduce the specifications and types of customized tools and measuring tools, facilitate production, and improve economy, the base hole system should be preferred. In the case that obvious economic benefits can be obtained, the base shaft system is chosen.

Selection principle of the base hole system.

Generally, the parts that are not easy to process are selected as the principle, that is to say, when the hole is matched with the shaft, if the shaft is easier to process, the base hole system is selected (in general, the base hole system is selected).

1. There are three types of fits when the hole is matched with the shaft, gap fit, interference fit and transition fit.

2. Gap fit: the size of the hole is greater than the size of the shaft;

3. Interference fit: the size of the hole is smaller than the size of the shaft;

4. Transitional cooperation: the cooperation between the first two and the other.

5. In the basis of tolerance and measurement, hole leasing mainly refers to the cylindrical inner surface, but also includes the non-cylindrical inner surface (the inclusive hood Hu surface formed by two parallel planes or facets). In the mechanical principle and other disciplines, there are relatively perfect regulations on the size of the hole and the deviation of the object.