what is interference in involute gear?

This thing only happen in case of involute gear.For constant valocity ratio the profile of both mating gear should be tangent all time.As we know that below the base circle it is not involute profile of teeth,so when tip of other teeth come in contact with the surface of other mating teeth below the base circle,there will happen undercut of teeth below base circle,it is called interference of gear.To avoid this normally undercut is already provided below the base circle of gear.

      In brief,the phenomenon when the tip of a tooth  undercuts the root on its mating gear is known as interference.

what is preferred series?

preferred series are the series of numbers obtained by geometric progression and rounded off.

what is basic preferred series?

There are five basic preferred series designated as R5,R10,R20,R40 and R80. Their step ratios are 1.58,1.26,1.12,1.06 and 1.03 respectively.

       Each series is established by talking the first number one and multiplying it by a step ratio to get second number. The second number is then multiplied by a step ratio to get third number. The procedure is continued until the complete series is built up.

ADVANTAGES OF PREFERRED SERIES:

1. The difference in two successive terms has fixed percentage.
2. Provide small step for small quantities and large steps for large quantities. It is in conformation with mode of vibration found in nature.
3. The product range is covered with minimum number of sizes without restricting the choise of the customers.