Design a cylindrical gear reducer, gear and shaft of the match, why is H7/r6?

I recently read a book on mechanical accuracy and felt puzzled. In the design of accuracy, the examples are given the largest, minimum gap, or maximum and minimum interference, and then determine the level of work according to this, and then choose the combination of categories and types.Associated with the design of the reducer, the H7/r6 of the gear and shaft, at that time I was direct reference to others, and I do not know why they chose this matchI feel that when I design the reducer, I don't know the maximum or minimum clearance or the maximum and minimum interference of the shaft and hole But the book "precision design" does say that matching is selected according to the allowable maximum or minimum clearance, or maximum and minimum interference.

Two principles1, the actual work needs, look at the status of work to determine the type of coordination, interference, transition, clearance fit. Such as the general bearings are all surplus.2, h7/r6's way of matching is based on experience, mechanical design is not mathematics, not necessarily this, but taking into account the effect in practice and the degree of difficulty in processing, empirical choice. It is the principle of design to meet the need and spend less

In fact, in the final analysis, "in the design of speed reducer, is based on the use of the requirements of the shaft, hole of the largest, minimum clearance, or maximum and minimum interference to determine" H7/r6 ", or first through other routes, selected H7/r6?" Both are "analogy" and "experience", which can only be used as reference for design (pre design), and can only be determined by experiment and use.

The disadvantage of interference fit, assembly and disassembly difficult, require special processes and tools, easy to pull the shaft, hole surface, and some can not be reused after disassembly.How to determine the tolerance of the gear hole and shaft? Analog method is used in general, reference to the same type, same power, comparable, good use of products, reference and selection. In the actual production, to test the design of products, meet the test standard to finalize the design, otherwise, through the experiment to find the problems and change the design (or the materials and Technology), until the product is qualified.

The exact tolerance fit between the gear hole and the shaft is not a fixed pattern (fixed type). Generally according to the size of the transmission power, the shaft speed, torque, assembly, degree of difficulty, etc., selected, of course, must first meet the use requirements.In general, the transmission power is small, you can select H7/m6, H7/p6, transmission power, you can choose H7/r6 or even H7/s6.The advantage of interference fit is that there is a "pre - tightening" between the shaft and hole. The contact rigidity is high, the impact resistance is high, and the utility model is suitable for high load.