General Tolerances

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General Tolerances

These tolerances apply as a general rule of thumb. Closer tolerances can be obtained depending on part design or the use of special procedures or secondary operations

  
Casting Tolerances
 
 
METRIC
 
  Up to 25 mm
  ± 0.127 mm
  Up to 50 mm
  ± 0.254 mm
  Up to 75 mm
  ± 0.381 mm
  Up to 100 mm
  ± 0.508 mm
  Up to 125 mm
  ± 0.635 mm
  Up to 150 mm
  ± 0.762 mm
 
  
Flatness 


Flatness refers to single plane surface and is usually a function of volumetric shrinkage

 
METRIC
 
  Range of nominal   dimension (mm   For Straightness /   Flatness (mm)
Over
Upto
As cast TIR
Machined TIR
   0   10   0.12   0.08
  20   25   0.15   0.10
  25   50   0.20   0.15
  50   75   0.30   0.20
  75  100   0.40   0.25
 100  150   0.55   0.35
 150  200   0.70   0.50
 200  300   0.95   0.70

 

 
Concentricity
 
 
METRIC
 
  Range of nominal   dimension (mm   For Roundness/   Concentricity (mm)
Over
Upto
As cast TIR
Machined TIR
   0   10   0.12   0.08
  20   25   0.15   0.10
  25   50   0.25   0.15
  50   75   0.40   0.25
  75  100   0.50   0.35
 100  150   0.70   0.45
 150  200   0.85   0.55
 200  300   1.00   0.70


 
Roundness-Solid Bars

Roundness is a function of normal shrinkage variations in the metal. Shrinkage variation increases with diameter and the tolerance required increases proportionately. A general rule of 0.127 mm per 25 mm may be applied.

Angles

As-cast tolerances of angles depend on their location in casting. They range from ± 1/2° for well supported positions to ± 2° where inherent distortion could be expected. Inclusion of gussets and ribs often minimizes distortion and many sections can be mechanically straightened.

Hole Positioning

0.127 mm per 25 mm from any single reference point.

Blind Holes

Blind holes can be cast if length does not exceed the diameter

Surface Finish

Average Ra value generally ranges between 3.20 to 5.50 microns.