Selecting correct tolerance of the machined parts during our design work, that is very useful for high efficient production.
Concerning the tolerance of machined parts, 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.
The fit of hole and shaft includes clearance fit,transition fit and interference fit.
1) If one-way intermittent operation and rotation displacement requires with low precision, low speed with flat key match, we can choose clearance fit, but need to have two screw at 90 degrees set positioning.
2) If it is one-way intermittent rotation, or forward and reverse motion, choose the transition fit, but also need to have a set screw.
3) If it is to transfer large torque,then choose interference fit,which usually requires pressure assembly or hot sleeve assembly.
The form and position tolerance is the supplement of the dimensional tolerance, so the selection of the tolerance zone should be less than the dimensional tolerance.
A machined part, the width of tolerance is 0.2mm, if require the parallelism of the both sides surface, it requires less than 0.2mm. Most of the time, the width of the tolerance request is not high, but the parallelism requirement is high. may is 0.05mm, so that the parallel is very important,usually influnece on assembly.
