Subject: Machine Design -I

Topic: Machine Design consideration

Difficulty: Medium

• Preferred Numbers are an important tool which minimize unnecessary variations in sizes.
• The complete range is covered by minimum number of sizes, which is advantageous for both producer and customer.
• With the acceptance of standardization, there is need to keep the standard sizes or dimensions of component in discrete steps.
• The sizes should be spread over wide range and at the same time, they should be spaced properly. e.g. diameters are to be standardized between 10mm to 25mm, then sizes should be 10mm, 12.5mm, 16mm, 20mm, and 25mm. This lead to use the geometrical series known as preferred series.
• It includes S5, S10, S20, S40, S80 series and each series has a series factor.
• For establishing a series, first a number is taken. By multiplying this number by a series factor, second number is obtained. Now by multiplying second number by a series factor, third number is obtained and so on.