Concerning the tolerance of machined components.
Generally, the dimensional tolerance is determined first.
And then the shape and position tolerance is determined. When we design the machined components, for the reasonable tolerance, we should consider the function needs first, the second is the processing technology.
The last is the assembly and maintenance technology.
For example, assembly hole and shaft, it is not only a round hole and shaft, can be square,but we usually use round, because the convenient processing. Traditional processing methods such as turning, milling, drilling and grinding,most of the circular processing. Now with the popularity of laser cutting and wire cutting,the application of special-shaped hole is also more.At the same tolerance level,the processing cost of square hole is higher than round hole.
Since the traditional method of processing is circular processing, the choice of hole and shaft will have a basic hole system and basic shaft system.
Generally, we can get hole by drilling, reaming, and milling. For convenient machining, we should choose to have readily available tools (drill, reamer,cutter) size, such as the diameter 14mm of cutting tool are very rare, we can choose 12mm,15mm or 16mm diameter of cutting tools,which is a conveninet purchase specifications. In this way, the manufacturing cost is very low. For example,choose diameter 30mm not 27mm, although your computing needs 27mm.
The fit of hole and shaft includes clearance fit, transition fit and interference fit.
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