TASK 70-31-00-220-001
1 . General.
The tolerancing of form and positional characteristics is indicated on drawings by means of either a written note or a feature control symbol (see Figure 1). The definition and use of these symbols is illustrated in Figure 2 and Figure 3.
Figure 1   Feature Control Symbols and Condition of Size
Figure 2   (Sheet 1 ) Dimensional Practices
Figure 2   (Sheet 2 ) Dimensional Practices
Figure 3   (Sheet 1 ) Inspection Terms
Figure 3   (Sheet 2 ) Inspection Terms
Figure 3   (Sheet 3 ) Inspection Terms
Figure 3   (Sheet 4 ) Inspection Terms
Figure 3   (Sheet 5 ) Inspection Terms
Figure 3   (Sheet 6 ) Inspection Terms
Figure 3   (Sheet 7 ) Inspection Terms
Figure 3   (Sheet 8 ) Inspection Terms
2 . Definitions.
Subtask 70-31-00-220-011
A.Datum.
The reference surface, line or point with respect to which other geometric characteristics are located and measured.
B.Condition of Size. See Figure 1.
Two conditions of size are recognized in positioning and form tolerancing: "Maximum Material Condition" (MMC) which is the condition least favorable for assembly with a mating part, and "Regardless of Feature Size" (RFS) in which form and positional tolerances apply regardless of the size of the feature specified.
3 . General Rules - MMC and RFS.
Subtask 70-31-00-220-012
A.When the material condition( Figure 1) of a specific positional or form tolerance is not stipulated on a drawing, the following rules apply:
 
Rule
Definition
 
Rule I:
Maximum Material Condition (MMC). When no modifier is specified, true position applies at MMC. Maximum material condition also applies to datum references other than plane surfaces.
 
Rule II:
Regardless of Feature Size (RFS). When no modifier is specified, concentricity tolerances and tolerances of form apply regardless of feature size. RFS also applies to datum references.
 
Rule III:
Where tolerances of form or position, or of datum references, apply to a screw thread, the tolerances apply to the pitch diameter.
4 . Glossary of Dimensional Inspection Terms.
Subtask 70-31-00-220-013
A.The following glossary provides interpretation and explanation of the dimensional system and practices used in the repair and restoration manuals.
 
Term
Definition
 
Axial clearance
Clearance measured in a direction parallel to the engine centerline.
 
Axial movement
Movement of a part in a direction parallel to the engine centerline.
 
Chamfer
(Refer to Detail B, Figure 3)
The bevel machined or formed at an edge to eliminate a sharp corner.
 
Concentricity
(Refer to Detail E, Figure 3)
The relationship between 2 circumferences having radii of different lengths, but the same center and direction.
NOTE:
Does not include total indentations or out-of-roundness.
 
Diameter
(Diametral)
A line across a circle, which intersects and is perpendicular to the centerline.
 
Diametral runout
(Refer to Detail C, Figure 3)
The total indicator reading (TIR) shown when an indicator contacts a cylindrical or conical surface, and the piece is rotated 360 degrees about an established axis. The reading includes both the eccentricity and out-of-roundness.
 
Drop
(Refer to Detail D, Figure 3)
The relative distance between 2 or more planes, measured from a common reference surface.
 
Eccentricity
(Refer to Detail E, Figure 3)
The distance between the axis of rotation and parallel axis through the geometric center of a part.
NOTE:
This condition does not include out-of-roundness or local imperfections.
 
Face runout
(Refer to Detail F, Figure 3)
The total indicator reading shown when the indicator contacts the face of a workpiece at a fixed distance from an established axis, while the workpiece is rotated 360 degrees about that axis.
NOTE:
This method does not measure concavity or convexity, which are related to the term "flatness".
 
Flatness
(Refer to Detail G, Figure 3)
The total deviation of a surface of a part from a true plane or straight edge.
 
Free-state
Free from all external forces or constraints.
 
Full indicator reading (FIR)
Refer to "total indicator reading" (TIR).
 
Parallelism
(Refer to Detail J, Figure 3)
Two or more straight lines or flat planes extending in the same direction, which are equidistant at all points.
 
Radial clearance
Clearance measured in a direction perpendicular to the engine centerline.
 
Radial flatness
(Refer to Detail K, Figure 3)
The total indicator reading shown when an indicator is removed radially across the face of a part at 90 degrees to an established axis. This measurement will show any existing concavity/convexity.
 
Radial movement
Movement of a part in a direction perpendicular to the engine centerline.
 
Radius
The distance from the center to the circumference of a circle or arc.
 
Restrained
The opposite of "free-state". The holding or clamping of a flexible part to a specified shape or configuration.
 
Roundness -
cylindricity
(Refer to Detail L, Figure 3)
Total radial variation from a true circle or cylinder; may be measured as the total indicator reading when the part is rotated 360 degrees about its own geometric center, or one-half the difference between the maximum and minimum diameters.
 
Sharp edge
An outside corner formed by the intersection of 2 flat surfaces or by the intersection of a concave radius and another surface, which form an abrupt angle. Burrs may extend from the surface machined last, and thus increase the sharpness of the edge.
 
Squareness -
perpendicularity
(Refer to Detail A, Figure 3)
The intersection of 2 lines, axes, planes or surfaces forming an angle of 90 degrees.
 
Straightness
(Refer to Detail H, Figure 3)
A tolerance zone of uniform width along a line that does not deviate in direction.
 
Total indicator
reading (TIR)
The mathematical difference between maximum and minimum readings of an indicator as it traverses one or more typical or specified lines on the surface being inspected.
 
True position
(Refer to Details M and N,
Figure 3)
The exact location, which can be calculated with known data, of a point or series of points on a part. True position may be stated either as degrees of arc from an established point, or as coordinate dimensions from horizontal and vertical centerlines or other features.