When 3-2-1 principle is used to support and locate a three dimensional work-piece during machining, the number of degrees of freedom that are restricted is
Answer: C
According to 3-2-1 principle, only the minimum locating points should be used to secure location of the work piece in any one plane.
(A) The work piece is resting on three pins A, B, C which are inserted in the base of fixed body. The work piece cannot rotate about the axis XX and YY and also it cannot move downward. In this case, the five degrees of freedom have been arrested.
(B) Two more pins D and E are inserted in the fixed body, in a plane perpendicular to the plane containing, the pins A, B and C. Now the work piece cannot rotate about the Z -axis and also it cannot move towards the left. Hence the addition of pins D and E restrict three more degrees of freedom.
(C) Another pin F in the second vertical face of the fixed body, arrests degree of freedom 9.