Theoretically exact dimensions

These dimensions are identified by enclosure in a rectangular box, e.g.

50

EQUI-SPACED

60°

030

and are commonly known as 'Boxed dimensions'. They define the true position of a hole, slot, boss profile, etc.

Boxed dimensions are never individually toleranced but are always accompanied by a positional or zone tolerance specified within the tolerance frame referring to the feature.

Symbols for geometrical characteristics

Type of tolerance

Characteristics to be toleranced

Symbol

Datum needed

Applications

Straightness

-

No

A straight line. The edge or axis of a feature.

Flatness

EJ

No

A plane surface.

Form

Roundness

o

No

The periphery of a circle.Cross-section of a bore, cylinder, cone or sphere.

Cylindricity

xy

No

The combination of circularity, straightness and parallelism of cylindrical surfaces. Mating bores and plungers.

Profile of a line

No

The profile of a straight or irregular line.

Profile of a surface

No

The profile of a straight or irregular surface.

Parallelism

//

Yes

Parallelism of a feature related to a datum. Can control flatness when related to a datum.

Perpendicularity

_L

Yes

Surfaces, axes, or lines positioned at right angles to each other.

Orientation

Angularity

Yes

The angular displacement of surfaces, axes, or lines from a datum.

Profile of a line

Yes

The profile of a straight or irregular line positioned by theoretical exact dimensions with respect to datum plane(s).

Profile of a surface

Yes

The profile of a straight or irregular surface positioned by theoretical exact dimensions with respect to datum plane(s).

Position

See note below

The deviation of a feature from a true position.

Concentricity and coaxiality

©

Yes

The relationship between two circles having a common centre or two cylinders having a common axis.

Location

Symmetry

Yes

The symmetrical position of a feature related to a datum.

Profile of a line

Yes

The profile of a straight or irregular line positioned by theoretical exact dimensions with respect to datum plane(s).

Profile of a surface

Yes

The profile of a straight or irregular surface positioned by theoretical exact dimensions with respect to datum plane(s).

Runout

Circular runout

Yes

The position of a point fixed on a surface of a part which is rotated 360° about its datum axis.

Total runout

Yes

The relative position of a point when traversed along a surface rotating about its datum axis.

Note: If two or more groups of features are shown on the same axis, they shall be considered to be a single pattern when not related to a datum.

Additional symbols

Description

Toleranced feature indication

Datum feature indication

Datum target indication

Theoretically exact dimension

Projected tolerance zone

Maximum material requirement

Least material requirement

Free state condition (non-rigid parts)

All around profile

Envelope requirement

Common zone

Symbols

Fig. 20.1A

Was this article helpful?

0 0
How To Become A Professional Pencil Drawing Artist

How To Become A Professional Pencil Drawing Artist

Realize Your Dream of Becoming a Professional Pencil Drawing Artist. Learn The Art of Pencil Drawing From The Experts. A Complete Guide On The Qualities of A Pencil Drawing Artist.

Get My Free Ebook


Responses

  • Jaakko Knihtil
    Is true position and theoretically exact the same?
    10 months ago
  • sadoc
    How to check tolerance of theoretical exact dimension?
    9 months ago
  • Sonny
    When to use theoretical exact dims?
    7 months ago
  • Pentti
    What is TED theoretically ezact diminsion?
    5 months ago
  • evan
    How to calculate position from theoretically exact dimensions?
    5 months ago
  • william
    When to use theoritcaly excact diemnsions?
    4 months ago
  • Anna-Liisa
    When to use a boxed dimension in engineers drawings?
    30 days ago
  • robert garcia
    What is a theoretically exact dimension?
    29 days ago

Post a comment