how the tolerances are decided?

Answer 1

Tolerances are decided by the demands of the application, the properties of the materials and the precision demanded of the function. For example you could not make a working engine that has a 1/8" gap between the diameter of the piston and the cylinder wall it rests inside, but it would be perfectly acceptable to have a 1/8" gap between the boards on a park bench. See what I mean, the tolerance depends on a mix of several things but mainly the function of the object.

Answer 2

The designer calculates what the permissible variation in fit or clearance is, and apportions that among the parts of the assembly. Sometimes, though, it runs the other way, and the tolerance drives the design. For example, I may want to use a less accurate fabrication process to reduce cost, and will have to design the assembly to work with the variations that result.

Answer 3

Well they yell at the part untill it finally breaks down crying then they hit their stopwatches and average out the time it took... lol No they just use a different manufacturing technique and/or higher/lower quality materials knowing from experience the worst case scenerio of how far off the part will range.

Answer 4

The limits of the machinery to produce the parts, the actual Fit and Function of the parts are just some of the factors in the tolerancing of the parts.

Answer 5

With the help of practical experience.

Answer 6

POWER OF ATTACK DECIDE THE POWER OF TOLERANCE