41
Fig. 4-6, A shows an angle measured in degrees,
minutes, and seconds.
Decimal units can also represent minutes and
seconds. See Fig. 4-6, B. To convert minutes into
a decimal, divide the minutes by 60. To convert
seconds into decimals, divide the seconds by 3600.
The following example shows the procedure.
Convert Minutes and Seconds to Decimal
Degrees
Degree = 3600 seconds
Minute = 60 seconds
Example 4-2:
Convert 45° 1′ 30″ to decimal degrees
Formula for calculating work
Decimal Degrees° =Degrees° + (minutes
÷
60)° +
(seconds
÷
3600)°
Solution:
Decimal Degrees° = 45° + (1
÷
60)° + (30
÷
3600)°
Decimal Degrees° = 45° + .0166° + .0083°
Decimal Degrees° = 45° + .0249°
Decimal Degrees° = 45.0249° (then round-up)
Decimal Degrees° = 45.025°
Coordinates can also locate angles. Linear
dimensions locate the coordinates for an angular
feature. Refer to Fig. 4-6, C.
DUAL DIMENSIONING
Parts manufactured in global markets may
utilize dual dimensioning on their drawings.
DUAL DIMENSIONING uses both US customary
and metric systems for measurement units. When
using dual dimensioning, the dominant system
appears first, followed by the alternate system. The
dominant system is the standard system used by
the manufacturer based on their location.
There are several formats of dual dimensioning.
The position of the values is one way to express
dual dimensioning. The values are placed above
and below the dimension line or next to each
other separated by a slash as shown in Fig. 4-7, A.
Another format uses brackets [ ] to separate each
system as shown in Fig. 4-7, B.
REFERENCE DIMENSIONS
REFERENCE DIMENSIONS are dimensions
without tolerances that only give basic
measurement information. Reference dimensions
can identify a part or be a general reference of
size. Since reference dimensions are not accurate
measurements, they do not have tolerances.
For that reason, they are not measurements for
machining or inspection purposes. A reference
dimension is placed between parentheses ( ) as
shown in Fig. 4-8.
One application for using reference dimensions
is for drawings of casted parts. The reference
dimensions specify a general size for setting up
the molds required for casting a part. However,
due to the nature of the process, the size of
each casted part will vary from the reference
dimensions. In this situation, the reference
dimensions are general notes on size and they
are not subject to tolerances.
Fig. 4-6. Angular dimensions are measured from a plane,
origin, or reference point. Examples A, B, and C represent the
same angle. A—Angular dimension in degrees, minutes, and
seconds. B—Angular dimension in decimal degrees.
C—Angular dimension by coordinates.
Fig. 4-7. Dual dimensioning gives measurements in both US
customary and metric values. A—The position of the values
indicates the main and alternate units. B—Brackets indicate
the alternate units.
ANGLE COORDINATES
A B
C
REFERENCE POINT
(VERTEX)
0° (STARTING ANGLE)
0° (STARTING ANGLE)
REFERENCE POINT
(VERTEX)
A
OR
B
ALTERNATE
UNITS
ALTERNATE
UNITS
ALTERNATE
UNITS
MAIN
UNITS
MAIN
UNITS
MAIN
UNITS
Dimensions and Tolerances