Formulae For Fundamental Deviations of Shafts up to size 500-3150mm

ISO 286 Tolerance Band "IT8" To "IT16"

Tolerance Band Given Below (IT8 To IT16) In Micrometer=(10^-3)mm

Calculation of International Tolerance Grades:

As mentioned before IT Grade have 18 standard tolerance. These IT Grades have their own numerical values for each dimater step given in the tables above. IT Grades IT01 to IT5 are the most accurate and used essetially for gauge. IT Grades IT6 to IT 16 are less accurate and are used for nonmating dimensions. International Grade can be calculated as given below;

T:International Tolerance grade in (μm)

D:Geometric mean dimension in millimeters (mm)

ITG:IT Grade (a positive integer)

Also T:International Tolerance can be showmen as;

"i": is standard tolerance unit/factor."i" for IT5 to IT 16 values can be calculated with the formula below;

Unit tolerance in (μm). To calculate D;

where, D (mm) is the geometric mean of the lower and upper diameters of a particular diameter step within which the chosen the diameter D lies. Standard Tolerance Unit/Factor the formula has parabolic relationship with the size of the products. As the size increases, the tolerance within which a part can be manufactured also increases.

The Standards Tolerance values corresponding to IT grades IT01, IT0, IT1, see the chart below

The Standards Tolerance values corresponding to IT grades IT5 to IT16, see the chart below

EXAMPLE:

Lets chose the diameter of the shaft 60mm, and Tolerance grade H8f7; Calculation for Fundamental deviation, Tolerances and Limit of size for Hole and, Shaft. Calculation of the Standard tolerance Unit;

The size range for 60mm Diameter would be 50-80mm from the ISO 286 table

Since design based on Hole basis, the fundamental deviation of hole is zero. Fundamental deviation for Shaft;