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Position Tolerance : GD&T Basics

  • Position tolerance in GD&T controls the variation in the location of a feature from exact true position. It is the total permissible variation in the location of a feature about its exact true position.
  • Material Condition (MMC & LMC), Projected Tolerance, Tangent Planes can be used along with position tolerance.
  • Tolerance zone for position tolerance can be two parallel planes, Cylinder or a sphere.
  • Positional tolerances is used to locate features of size from datum planes such as a hole or key-way and used to locate features coaxial to a datum axis.
  • In cylindrical features, the position tolerance zone is typically a cylinder within which the axis of the feature must lie.

Representation Of Position Tolerance


Tolerance Zone For Position Tolerance

 

 

Tolerance Zone Without Diameter and MMC Modifier

  • Tolerance Zone will be a rectangle through the thickness of part with length equal to value of engineering tolerance.
  • Centre of circle should lie within this tolerance zone will be acceptable

 

 

 


 

 

Tolerance Zone With Diameter and without MMC Modifier

  • Tolerance Zone will be a circular cylinder with diameter equal to value of engineering tolerance.
  • Centre of circle within this tolerance zone will be acceptable

 

 


 

Tolerance Zone With Diameter & MMC Modifier

  • If the size of hole is at LMC , bonus tolerance can be added with positional tolerance.
  • At MMC Bonus Tolerance will be = (Dimension At LMC – Dimension at MMC) / 2
  • Tolerance Zone will be a circular cylinder with diameter = (Geometric Tolerance + Bonus Tolerance) 0.3 mm
  • Centre of circle within this tolerance zone will be acceptable

 

 


 

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