DIMENSIONING - tatroracing
DIMENSIONING - tatroracing
Why do we need to dimension drawings?
Dimensions and notes define the size, location, finish
and other requirements to fully define what you want
Why is dimensioning important?
Even if you make a drawing to scale, it
would be difficult to determine the exact
precision that is needed.
It would be time consuming to measure
each of the lines to determine
The basis for modern part dimensioning is
the need for interchangeable parts (being able to
buy something off the shelf that fits what you already have)
Generally, dimensioning involves identifying
the size and location dimensions.
Size Dimensions determine the overall
size and shape of a drawing.
Location Dimensions typically determine
where different entities are located within
When locating an item within the
drawing (locating a hole or other
object) always give the horizontal and
vertical position as it relates to the
Then give the size of the object
Eg. Where is the object located and
how big is it?
Most dimensions consist of three types of lines
A Dimension Line is a thin, dark, solid
line that is terminated by an
An Extension Line is a thin, dark, solid
line that extends from a point on the
drawing to which a dimension refers.
A Centerline is a thin, dark line alternating long and
short dashes that is commonly used as an
extension line in location holes or other symmetrical
Worksheet # 15
Dimensions: Architectural Vs. Engineering
Architectural dimensions are placed
above the dimension line
Engineering dimensions are placed
within the dimension line
Unidirectional System: where all
dimensions are read from the bottom
of the sheet (like a book)
Aligned System: all the dimensions are
aligned with the surface that they
represent (read from bottom or right
side of sheet)
Typically, the spacing between the
nearest dimension line and the object
should be about .375 or 3/8” away
while all other dimensions should be
.25 or ¼” apart thereafter.
When stacking dimensions, the shortest
dimension goes closest to the object, while
the longest (or overall) appears furthest.
Dimension Lines typically should not cross
extension lines or other dimension line
LABEL THE TYPE OF DIMENSIONING THAT IS USED IN EACH OF TH
When drawing Arrowheads they
should be long and lean at a ratio of
In Architecture this is different!
A Leader is a thin solid line that directs the
viewer’s attention to a note or dimension.
A Leader with an arrow identifies a
A Leader with an dot identifies a surface.
Try not to draw leaders so that they are
horizontal or vertical (and/or to long)
A Leader to a circle should be drawn so that
it would pass through the center of the circle
Dimensioning Arcs Vs. Circles
When dimensioning an arc use the
radius symbol (R)
When dimensioning a circle use the
diameter symbol ( )
Datum Line Vs Chain Style
In Datum Line dimensioning, you start
with a single reference line and then
each dimension is developed off that
Chain Style Dimensioning
Chain style is where the dimensions
are linked from one to the next.
(typically less accurate when dealing with high
In Chain Style Dimensioning
tolerances are added to each
Takes up less room when
dimensioning area is
When dimensioning, it is good
technique to avoid listing the
dimension more than once through out
If you need to list a dimension more
than once, for accuracy or ease of
viewing, you must encase the
dimension within a set of brackets.
Dimensioning a Circular Object
When dimensioning a circle, or an
object that is defined by an arc, it is
good technique to dimension to the
center point and then give the radius.
Angular Dimensions Vs. Point Locations
You can draw angular surfaces by knowing a point
of reference and the angle of the surface, or you
can give two points of reference.
Rectangular, Polar, or Equally Spaced
Rectangle dimensioning refers to measuring
change in horizontal and vertical positioning.
Polar measures the angular difference between
objects (usually with a reference point).
Equally spaced gives a center locations of the
entities, the number required, and then indicates
the objects are all equally spaced (meaning same
angle occurs between them)
Examples of each…
List each as you identify them.
The most important question that you
could ask yourself is “Can this be
drawn accurately with the information
that I given the drawing?
Please complete worksheets