PROBLEMS IX DIMENSIONS AND TOLERANCES 



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Fig. 10 — Functional datum planes of complicated switch frame 



Dimensions to datum line "X" or "Y" of the drawing of the frame refer to functional 

 datum planes 1, 2 or 3 described below. Points "P" and "Q" are gauge points used in 

 establishing these datum lines and planes. Points "P" and "Q" shall be half-way between 

 the surfaces "A" and "B" and "C" and "D" respectively and 4.358 in. from the plane of 

 surfaces "IM" and "N" on the mounting lugs. 



Datum line "X" shall pass through the points '"P" and "Q". 



Plane 1 shall be parallel to surfaces "M" and "N" and shall include datum line "X". 



Plane 2 shall be perpendicular to plane 1 and shall also include datum line "X". 



Plane 3 shall be perpendicular to plane 1 and to plane 2 at the point "P". 



Datum line "Y" passes through point "P" and is the intersection of planes 2 and 3. 



