Explain the 3-2-1 Principle of Location

• A work piece can be positively located by means of 6 pins so positioned that collectively they restrict the work piece in nine of its degree of freedom.

   Figure: The 3-2-1 principle of location

• This is known as six point location method. Three of these pins are in first plane and two in the second plane perpendicular to the first and one in the third plane perpendicular and adjacent to the both first and second planes.