Various characteristics and features require unique methods of dimensioning.
- Chords, Arcs, and Angles
- Rounded Ends and Slotted Holes
- Rounded Corners
- Outlines Consisting of Arcs
- Irregular Outlines
- Grid System
- Symmetrical Outlines
- Round Holes
- Counterbored Holes
- Countersunk and Counterdrilled Holes
- Chamfered and Countersunk Holes on Curved Surfaces
- Machining Centers
- Rods and Tubing Details
- Screw Threads
- Surface Texture Requirements
- Involute Splines
- Castings, Forgings, and Molded Parts
The diameter symbol precedes all diametral values. See Fig. 1-21 and para. 3.3.7. Where the diameter of a spherical feature is specified, the diametral value is preceded by the spherical diameter symbol. See Fig. 3-11 and para. 3.3.7. Where the diameters of a number of concentric cylindrical features are specified, such diameters should be dimensioned in a longitudinal view if practical.
Each radius value is preceded by the appropriate radius symbol. See Figs. 1-22 and 3-11 and para. 3.3.7. A radius dimension line uses one arrowhead, at the arc end. An arrowhead is never used at the radius center. Where location of the center is important and space permits, a dimension line is drawn from the radius center with the arrowhead touching the arc, and the dimension is placed between the arrowhead and the center. Where space is limited, the dimension line is extended through the radius center. Where it is inconvenient to place the arrowhead between the radius center and the arc, it may be placed outside the arc with a leader. Where the center of a radius is not dimensionally located, the center shall not be indicated. See Fig. 1-22.
Center of Radius
Where a dimension is given to the center of a radius, a small cross is drawn at the center. Extension lines and dimension lines are used to locate the center. See Fig. 1-23. Where location of the center is unimportant, the drawing must clearly show that the arc location is controlled by other dimensioned features such as tangent surfaces. See Fig. 1-24.
Where the center of a radius is outside the drawing or interferes with another view, the radius dimension line may be foreshortened. See Fig. 1-25. That portion of the dimension line extending from the arrowhead is radial relative to the arc. Where the radius dimension line is foreshortened and the center is located by coordinate dimensions, the dimension line locating the center is also foreshortened.
On a 2D orthographic drawing, where a radius is dimensioned in a view that does not show the true shape of the radius, TRUE is added before the radius dimension. See Fig. 1-26. This practice is applicable to other foreshortened features as well as radii. See Fig. 4-28.
Where a part has a number of radii of the same dimension, a note may be used instead of dimensioning each radius separately.
Where a spherical surface is dimensioned by a radius, the radius dimension is preceded by the symbol SR. See Fig. 1-27.
Chords, Arcs, and Angles
The dimensioning of chords, arcs, and angles shall be as shown in Fig. 1-28.
Rounded Ends and Slotted Holes
Features having rounded ends, including slotted holes, are dimensioned using one of the methods shown in Fig. 1-29. For fully rounded ends, the radii are indicated but not dimensioned. For features with partially rounded ends, the radii are dimensioned. See Fig. 1-30.
Where corners are rounded, dimensions define the edges, and the arcs are tangent. See Fig. 1-31.
Outlines Consisting of Arcs
A curved outline composed of two or more arcs is dimensioned by giving the radii of all arcs and locating the necessary centers with coordinate dimensions. Other radii are located on the basis of their points of tangency. See Fig. 1-32.
Irregular outlines may be dimensioned as shown in Figs. 1-33 and 1-34. Circular or noncircular outlines may be dimensioned by the rectangular coordinate or offset method. See Fig. 1-33. Coordinates are dimensioned from base lines. Where many coordinates are required to define an outline, the vertical and horizontal coordinate dimensions may be tabulated, as in Fig. 1-34.
Curved pieces that represent patterns may be defined by a grid system with numbered grid lines.
Symmetrical outlines may be dimensioned on one side of the center line of symmetry. Such is the case where, due to the size of the part or space limitations, only part of the outline can be conveniently shown. See Fig. 1-35. One-half the outline of the symmetrical shape is shown and symmetry is indicated by applying symbols for part symmetry to the center line. See ASME Y14.2.
Round holes are dimensioned as shown in Fig. 1-36. Where it is not clear that a hole goes through, the notation THRU follows a dimension. Where multiple features are involved, additional clarification may be required. The depth dimension of a blind hole is the depth of the full diameter from the outer surface of the part. Where the depth dimension is not clear, as from a curved surface, the depth should be dimensioned pictorially. For methods of specifying blind holes, see Fig. 1-36.
Counterbored holes may be specified as shown in Fig. 1-37. Where the thickness of the remaining material has significance, this thickness (rather than the depth) is dimensioned. The relationship of the counterbore and the hole shall be specified. See Figs. 7-24 and 7-25. For holes having more than one counterbore, see Fig. 1-38. Where applicable, a fillet radius may be specified.
Countersunk and Counterdrilled Holes
For countersunk holes, the diameter and included angle of the countersink are specified. For counterdrilled holes, the diameter and depth of the counterdrill are specified. Specifying the included angle of the counterdrill is optional. See Fig. 1-39. The depth dimension is the depth of the full diameter of the counterdrill from the outer surface of the part.
Chamfered and Countersunk Holes on Curved Surfaces
Where a hole is chamfered or countersunk on a curved surface, the diameter specified on the drawing applies at the minor diameter of the chamfer or countersink. See Fig. 1-40.
Where the diameter of the spotfaced surface is specified, either the depth or the remaining thickness of material may be specified. If no depth or remaining thickness of material is specified, the spotface is the minimum depth necessary to clean up the surface to the specified diameter. Where applicable, a fillet radius may be indicated for the spotface. In some cases, such as with a through hole, a notation may be necessary to indicate the surface to be spotfaced. See Fig. 1-41. A spotface may be specified by note only and need not be shown pictorially.
Where machining centers are to remain on the finished part, they are indicated by a note or dimensioned on the drawing. See ASME B94.11M.
Chamfers are dimensioned by a linear dimension and an angle, or by two linear dimensions. See Figs. 1-42 through 1-45. Where an angle and a linear dimension are specified, the linear dimension is the distance from the indicated surface of the part to the start of the chamfer. See Fig. 1-42.
Chamfers Specified by Note
A note may be used to specify 45° chamfers on perpendicular surfaces. See Fig. 1-43. This method is used only with 45° chamfers, as the linear value applies in either direction.
Where the edge of a round hole is chamfered, the practice of para. 220.127.116.11 is followed, except where the chamfer diameter requires dimensional control. See Fig. 1-44. This type of control may also be applied to the chamfer diameter on a shaft.
Non-Perpendicular Intersecting Surfaces
Two acceptable methods of dimensioning chamfers for surfaces intersecting at other than right angles are shown in Fig. 1-45..
Keyseats are dimensioned by width, depth, location, and if required, length. The depth may be dimensioned from the opposite side of the shaft or hole. See Fig. 1-46.
Knurling is specified in terms of type, pitch, and diameter before and after knurling. Where control is not required, the diameter after knurling is omitted. Where only a portion of a feature requires knurling, the location and length of the knurl shall be specified. See Fig. 1-47.
Knurling for Press Fit
Where required to provide a press fit between parts, knurling is specified by a note that includes the type of knurl required, its pitch, the toleranced diameter of the feature before knurling, and the minimum acceptable diameter after knurling. See Fig. 1-48.
For information on inch knurling, see ANSI/ASME B94.6.
Rods and Tubing Details
Rods and tubing may be dimensioned in three coordinate directions and toleranced using geometric tolerances or by specifying the straight lengths, bend radii, angles of bend, and angles of twist for all portions of each feature. This may be done by means of auxiliary views, tabulation, or supplementary data.
Methods of specifying and dimensioning screw threads are covered in ASME Y14.6.
Surface texture symbols specify the limits on surface roughness, surface waviness, lay, and flaws. A machined surface may be compared to the ocean surface in that the ocean surface is composed of small ripples on larger waves. See Fig. 4-25. Basic surface texture symbols are used on the drawing shown in Fig. 4-3.
Methods of specifying involute spline requirements are covered in the ANSI B92 series of standards.
Castings, Forgings, and Molded Parts
Methods of specifying requirements peculiar to castings, forgings, and molded parts are covered in ASME Y14.8.