Dimensioning
Dimensioning
Dimensioning
The Ames Lettering Guide is a transparent plastic device composed of a frame holding a disc
containing columns of holes. The vertical distances between the holes may be adjusted quickly to
the desired spacing for guide lines or section lines by simply turning the disk to one of the settings
indicated at the bottom of the disk.
The numbers at the bottom of the disc indicate heights of letters in thirty-seconds of an inch.
Thus for the Number 4 setting, the lettering height would be 4/32” or 1/8”.
Dimensioning
The center column of holes (evenly spaced holes) is used primarily to draw guide lines for
numerals, fractions, and general lettering. The height of whole numbers and general lettering will
be two units and the height of fractions will be four units. Since the spaces are equal, these holes
can also be used to draw equally spaced section lines.
The sides of the guide are used to draw vertical or inclined guide lines.
Dimensioning
The Ames Lettering Guide is a transparent plastic device composed of a frame holding a disc
containing columns of holes. The vertical distances between the holes may be adjusted quickly to
the desired spacing for guide lines or section lines by simply turning the disk to one of the settings
indicated at the bottom of the disk.
The numbers at the bottom of the disc indicate heights of letters in thirty-seconds of an inch.
Thus for the Number 4 setting, the lettering height would be 4/32” or 1/8”.
Dimensioning
The center column of holes (evenly spaced holes) is used primarily to draw guide lines for
numerals, fractions, and general lettering. The height of whole numbers and general lettering will
be two units and the height of fractions will be four units. Since the spaces are equal, these holes
can also be used to draw equally spaced section lines.
The sides of the guide are used to draw vertical or inclined guide lines.
Dimensioning
Overview:
Graphical entities on engineering drawings describe shape and position. Dimensions and notes
describe size and necessary manufacturing processes if the engineering drawing is to be a
complete instruction for the shop technician.
Dimensions describe the size and location of features of an object. The correct placement of
dimensions is strictly prescribed by an extensive list of drawing conventions.
Dimensioning
Size Description
In addition to a complete shape description of an object, a drawing of the design must also give a
complete size description, that is, it must be dimensioned.
A drawing submitted to production should show the object in its completed condition (shape
description) and should contain all necessary information to bring it to that final state.
Only those dimensions needed to produce and inspect the part against the design specifications
should be given, not the dimensions use to make the drawing.
Dimensioning
Learning to Dimension (keys to good dimensioning)
1.
The student must learn the technique of dimensioning: the character of the lines, the
spacing of dimensions, the making of arrowheads, and so forth.
2.
The student must learn the rules of placement of dimensions of the drawing.
3.
The student should learn the choice of dimensions.
Dimensioning
Lines used in dimensioning:
Dimension line: A dimension line is a thin, dark line terminated by arrowheads and indicates the
extent of the dimension.
Extension line: An extension line is a thin, dark line that extends from a point on the drawing to
which a dimension refers.
Dimensioning
Spacing of dimension lines should be uniform throughout the drawing. The dimension line nearest
the object should be spaced at least 3/8” away from the object.
All other dimension lines should be spaced at least 1/4” apart.
A 1/16” gap is left where the extension line would join the object outline and extends 1/8” past the
outermost dimension line.
Dimensioning
Center Lines:
Center Line: A center line is a thin, dark line composed of alternate long and short dashes and is
used to represent axes of symmetry, locate holes, and to denote centers.
Center lines are commonly used as extension lines.
When a center line crosses over an object line, it crosses the object line without a gap.
Dimensioning
Arrowheads:
Arrowheads indicate the extent of dimensions.
Arrowheads are drawn freehand. They should be uniform in size and style throughout the
drawing.
The length of an arrowhead should be equal to the height of the lettering and the length and width
should be in a ratio of 3:1
Dimensioning
Leaders:
A leader is a thin, dark, solid line that leads from a note or dimension and terminates in an
arrowhead.
Arrowheads should always terminate on a line or edge of a hole.
A leader to a circle should be radial and appear to pass through the center.
Leaders should cross as few lines a possible and should never cross each other.
Dimensioning
Dimension Figures:
The importance of good lettering of dimension figures cannot be overstates.
Always use guidelines for all dimension numbers and text.
Legibility should never be sacrificed by crowding dimension figures into limited spaces.
As shown in the examples, if there is only enough room for the figure, the arrowheads
are placed outside the extension lines and if the space is too small for both the
arrowheads and the dimension figure both the arrowheads and figure are placed
outside the extension lines.
Dimensioning
Placement of dimension and extension lines:
The correct placement of dimension lines and extension lines are shown in figure (a). The shorter
dimensions are placed nearest the object.
Dimension lines should never cross an extension line (figure b).
It is acceptable to cross extension lines with other extension lines but the extension lines should
never be shortened (figure c).
A dimension line should never coincide with or form a continuation of any other line of the drawing
(figure d).
Dimensioning
Dimensions should be lined up and grouped together as much as possible.
Dimensioning
When extension lines and center lines cross visible
object lines gaps should not be left in the lines.
Dimensioning
Dimension Figures:
In a group of parallel dimension lines, the numerals should be
staggered (figure a) and not stacked up one above the other (figure b).
Dimensioning
Direction of dimension figures:
There are two systems of reading direction for dimension figures, the unidirectional system and
the aligned system.
Unidirectional system: the dimension figures are lettered horizontally on the sheet and are read
from the bottom of the drawing (figure a)
Aligned system: the dimension figures are aligned with the dimension lines and are read from the
bottom of the drawing or the right side (figure b).
Dimensioning
Contour Dimensioning:
Dimensions should be given where the shapes show true size and true shape.
Dimensioning
Dimensioning Angles:
Angles are dimensioned by giving the angle in degrees and a linear dimension (figure a) or by
dimensioning the two legs of a right triangle (figure b).
In all cases whether in the unidirectional system or in the aligned system the dimension figures
for angles are lettered horizontally (figures c, d, e, f).
Dimensioning
Dimensioning Arcs:
A circular arc is always dimensioned in the view in which its true shape is shown by giving
the numeral denoting its radius.
Dimensioning
Dimensioning a Cylinder:
The general method of dimensioning a cylinder is to give both its diameter and length in the
rectangular view. A leader can also be used to dimension the circular view.
Dimensioning
Dimensioning Prisms:
The height and width
dimension of a prism should
be given in the front view and
the depth dimension given in
the top or right-side view.
Horizontal and vertical
dimensions should be kept in
line.
Dimensioning
Dimensioning Holes:
Holes are dimensioned using leader lines pointing to the hole and shown where the hole appears
circular.
Dimensions and notes should always be lettered horizontally of the drawing.
Dimensioning
The diameter symbol () should be given before all diameter dimensions.
Dimensioning
Locating Holes:
Location dimensions for
holes are given in the
circular view of the holes
where the holes appear
true size and true shape.
Dimensioning
Locating holes about a center:
Holes equally spaced about a common center may be dimensioned by giving the diameter of the
circle of centers (figure a).
Unequally spaced holes are located by dimensioning the bold circle diameter plus angular
measurements (figure b).
Where greater accuracy is required, coordinate dimensions should be given (figure c).
Dimensioning
Dimensioning rounded-end
shapes:
The method for dimensioning
rounded-end shapes depends of
the degree of accuracy required.
Shown are examples of
dimensioning rounded-end
shapes.
Dimensioning
Superfluous Dimensions:
All necessary dimensions must be
shown on a drawing.
Avoid giving unnecessary or
superfluous dimensions.
Dimensions should not be repeated
or the same dimension given in two
different ways.
Dimensioning
Notes:
Local notes that apply to specific
operations only are connected by a
leader to the point at which such
operations are performed.
The leader should be attached to the
front of the first word of a note or after
the last word.
Notes are always lettered horizontally
on the drawing sheet.
Dimensioning
Notes:
Dimensioning
Dimensioning Chamfers:
A chamfer is a beveled or
sloping edge.
A chamfer is dimensioned by
giving the length of the offset
and the angle (figure a).
A chamfer can also be
dimensioning using a leader
line (figure b).
Dimensioning
Dimensioning Keyways:
Dimensioning
Dimensioning knurls:
A knurl is a roughened surface to provide a better
handgrip or to be used for a press fit between two parts.
A knurl is dimensioned by specifying the pitch of the
knurl, the type of knurling, and the length of the knurled
area.
Dimensioning
Mr. Ference’s rules for dimensioning:
1.
Always use guidelines for all dimension numbers and text.
2.
Spacing for all dimension lines should be uniform and consistent.
3.
Never cross a dimension line.
4.
Place dimensions where the feature shows both true size and true shape.
Dimensioning
Dimensioning