Blueprint Reading for the Machine Trades, Sixth Edition Unit 2: Dimensioning Systems

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### Blueprint Reading for the Machine Trades, Sixth Edition Unit 2: Dimensioning Systems

Russ Schultz and Larry Smith

PowerPoint presentation created by LaVonne Vichlach

Dimensioning Systems
• Four different systems of dimensioning used in U.S. and Canada
• Fractional inch
• Decimal inch
• Dual dimensioning
• SI Metric
Fractional type steel rules divided into units of:
• 1/16
• 1/32
• 1/64
• Major graduation accentuated by longer lines
• Some have small numbers printed adjacent to lines
Fractional Dimensioning
• Always reduce a fraction to its lowest terms
• If numerator is even number-it can be reduced

Record the scale length identified by

• 3/4

1

Record the scale length identified by

• 1 5/8

2

Record the scale length identified by

• 2 7/16

3

• 3 3/16

Record the scale length identified by

4

• 3 15/16

Record the scale length identified by

5

• 13/16

Record the scale length identified by

6

• 1 ¾

Record the scale length identified by

7

• 2 11/16

Record the scale length identified by

8

• 3 17/32

Record the scale length identified by

9

• 3 31/32

Record the scale length identified by

10

Decimal Scales
• Subdivided into units of 1/10, 1/20, 1/50, or 1/100 in.
• 1/50 is sufficient for most applications
• With 50 increments to an inch each increment =.02 in.
• Reading between increments-capable of determining closest .01 inch measurement
Decimal Scales
• Closer measurements require using micrometer, vernier or dial calipers
• Major graduations are accented by longer lines-usually every 1/10 in.
• Popular scales graduation style has .04 and .06 increments slightly longer than .02 and .08
• .80

Record the scale length identifiedby...

1

• 1.60

Record the scale length identified by…

2

• 2.50

Record the scale length identified by…

3

• 3.32

Record the scale length identified by…

4

• 3.86

Record the scale length identified by…

5

Decimal Dimensioning
• Drawing may be dimensioned using two- or three-place decimals
• Amount of tolerance is determined by number of decimal places
Decimal Dimensioning
• .50 may have tolerance of ± .01
• .500 may have tolerance of ± .001
• .5000 may have tolerance of ±.0001
Decimal Dimensioning
• Converting fractions to decimals-results in too many decimal places
• Need to round off those numbers to desired places
Decimal Dimensioning
• Rule #1-When the figure following the last digit to be retained is greater than 5---increase the last number by one
• .016 becomes .02
• .047 becomes .05
• .078 becomes .08
Decimal Dimensioning
• Rule #2-When the figure following the last digit to be retained is less than 5---retain the last number
• .031 becomes .03
• .062 becomes .06
• .093 becomes .09
Decimal Dimensioning
• Rule #3-When the figure following the last digit to be retained is exactly 5 and the figure to be retained is odd---increase the last number by one
• .375 becomes .38
• .875 becomes .88
Decimal Dimensioning
• Rule #4-When the figure following the last digit to be retained is exactly 5 and the figure to be retained is even---retain the last number
• .125 becomes .12
• .625 becomes .62
Decimal Dimensioning
• Rule #3 and #4 are different
• Established to even numbers as often as possible
• Even numbers are preferred
• Decimal numbers divided by two-e.g.-diameter/2 = radius-----results will contain same number of decimal places
Decimal Rounding Quiz

.11

• .109 =
• .125 =
• .156 =
• .234 =
• .438 =
• .547 =
• .562 =

.12

.16

.23

.44

.55

.56

Decimal Rounding Quiz

.64

• .641 =
• .797 =
• .875 =
• 1.056 =
• 1.672 =
• 2.205 =
• 2.454 =

.80

.88

1.06

1.67

2.20

2.45

Decimal Rounding Quiz

3.34

• 3.335 =
• 3.767 =
• 5.555 =
• 6.665 =
• 7.045 =
• 8.885 =

3.77

5.56

6.66

7.04

8.88

Metric Dimensioning
• Metric increment of measure is millimeter
• Will be noted if different
• Dual dimensioning system-SI Metric-used in U.S. and Canada
• Convert a metric dimension to inches by multiplying it by .03937
Metric Dimensioning
• Conversion charts are available to provide converted dimensions
• Metric scales are available and can be used-eliminating need for conversion
Metric Dimensioning
• Metric scales
• Have graduations every millimeter of half-millimeter
• Designated “mm” or “1/2 mm”
• Every fifth millimeter is accentuated by a longer line
• Every tenth millimeter is identified by a number

Record the scale length identified by

• 20 mm

1

Record the scale length identified by

2

• 35 mm

Record the scale length identified by

3

• 51 mm
• 77.5 mm

Record the scale length identified by

4

• 93.5 mm

Record the scale length identified by

5

Blueprints
• Blueprinting-Term can be interpreted as
• Drawing
• Picture
• Contains information
• Required sizes
• Tolerances
• Essential requirements
• Notes and instructions
Engineering Drawings
• Original drawing made by drafter or engineer
• Prints are referred to as engineering drawings
• Also referred to as blueprints (more common term)
Engineering Drawings
• Standardized drawings
• “A” size is 8 ½ x 11 inches
• “B” size is 11 x 17 inches
• “C” size is 17 x 22 inches
• “D” size is 22 x 34 inches
• “E” size is 34 x 44 inches
What are the basic dimensions of the A-size drawing?Engineering Drawings

8 ½ X 11

2. If C-size is twice as large as B-size, how much larger is it than A-size?

4X

Will an E-size print fold to fit in the same envelope with an A-size print?

A2

Engineering Drawings

YES

4. What metric size is twice as large as the A3 size?

Title Blocks
• Each drawing contains a Title Block
• Drawing number is most prominent lettering in title block
• Lettered larger to stand out
• Scale determines the size of the object drafted
Title Blocks
• Mechanical drawings may be reduced to
• Half size
• Quarter size
• One eighth size
Title Blocks
• Mechanical drawings may be enlarged
• Double
• Four times
• Ten times
Title Blocks
• Half scale---1/2, 1:2, or ½”=1”
• Twice scale-2/1, 2:1, 2-1, 2”=1” or 2X
• Arrangement of numerals indicates relationship
Title Blocks
• Refer to scale as the “Do Scale”
• “D” stands for the drawing
• “O” stands for the object
• Sale of 1:2 means
• The drawing is 1 inch
• Object is 2 inches
• A “Do Scale” of 2:1 means
• The drawing is 2 inches
• The object is one inch or one half the drawing size
Drawing Notes
• Local notes-apply to specific item or area
• Direct notes to point of application
• General notes apply to whole drawing or product
• Machining
• Heat treat
• Material
• Tolerances
Drawing Notes
• Abbreviations are used in notes
• Keep them brief
UNLESS OTHERWISE SPECIFIED

METRIC UNITS ARE MILLIMETERS

FILS & RNDS ARE .12R

Drawing Notes-General
5 HOLES EQL SP ON 6.000BC

.344 DR, .500 CBORE, .30 DP

.281 DR, 82° CSK, .53 DIA

Drawing Notes-Local
Drawing Notes Quiz
• What type of note applies to an entire drawing?

General

Drawing Notes Quiz
• What type of line is used with local notes?

Drawing Notes Quiz
• Where do general notes appear on a drawing?

Above the title block

Drawing Notes Quiz
• Interpret the abbreviations SYM and CL used in the third general note.

Symmetrical and centerline

Drawing Notes Quiz
• Interpret the abbreviations DR and CSK used in the third local note.

Drill and countersink

Single-View Drawings
• Sometimes adequate to describe object
• Material thickness is listed
Detail Drawings
• “Production drawings” and “working drawings” are general terms
• Includes all types of engineering drawings
Detail Drawings
• Detail drawings include
• Sufficient number of views
• Dimensions
• Notes
• Other pertinent information
Centerlines
• Intersecting centerlines drawn through each hole
• Used for location-centerlines are extended outside view and dimensions are added
• Radii are the same-often share a common axis-common design practice
• Internationally recognized symbol for diameter
• Use in place of the abbreviation DIA
• Number of holes indicated
• Overall dimensions can be calculated
• Remaining material around hole can be calculated
• Remaining material around hole can be calculated

1. What is the part number?

11A001

2. What is the name of the part?

3. What is the drawing size? (A, B, or C)

A

4. What scale is the drawing?

1:1

5. Use words to explain the answer to question 4.

Actual size

6. How thick is the part?

.06

7. Is the part symmetrical?

Yes

8. Which system of dimensioning was used? (Refer to page 21.)

Decimal

9. What is the fractional equivalent of the center hole size? (Refer to the equivalency chart, page 25.)

2 3/16

• What is the fractional equivalent of the mounting hole spacing? (Refer to the equivalency chart, page 25.)

3 5/8

11. Calculate the longest overall dimension of the part.

4.24

12. Calculate the overall dimension of the part (height.)

2.88

13. Calculate the material remaining between the large hole and the nearest outside edge.

.345

14. Calculate the material remaining between the small hole and the nearest outside edge.

.155

15. Calculate the material remaining between the large hole and the nearest small hole.

.56

Break Lines
• Permits removal of a portion of view
• Paper size is smaller
• Drawing scale can get smaller
• Portion removed must be uniform in shape
Break Lines

Drawing is full size and does not require a “B” size drawing

Typical Dimensions
• Entered after a dimension
• Means all other similar dimensions are same as one marked “TYP”
• Eliminates repetition of dimensions
• Saves on drawing space
Symmetry
• Indicated by note
• Indicated by view’s centerline carrying abbreviation
Exercise

Enter dimensions for the letters provided.

Bottom Plate

1. What type of line was drawn to indicate symmetry?

Centerline

Bottom Plate

2. What word is abbreviated TYP?

Typical

Bottom Plate

3. What is the thickness of the plate?

.25

Bottom Plate

4. How many round holes does the plate contain?

10

Bottom Plate

5. What is the fractional equivalent of the small hole diameter?

9/32

Bottom Plate

6. How much material remains between a .62 Dia. hole and the nearest outside edge?

.25

Bottom Plate

7. How much material remains between a .28 Dia. hole and the nearest outside edge?

.16

Bottom Plate

8. Calculate the longest overall dimension of the plate.

6.76

Tolerances
• Tolerances are assigned to every dimension
• Assign maximum acceptable deviation-tolerance
• Shown with dimension
• Shown in the title block as a general tolerance
Tolerances
• General tolerances commonly assigned using decimals
• Decimal dimension and tolerance have same number of places
• Most commonly expressed bilaterally-not always equal in both directions
Tolerance Quiz

1. What is the two place decimal tolerance in Example A?

 .03

Tolerance Quiz

2. What is the tolerance for drilled holes in Example A?

+ .010

-.002

Tolerance Quiz

3. What is the three-place decimal tolerance in Example B?

 .004

Tolerance Quiz

4. What is the fractional tolerance in Example C?

 1/64

Tolerance Quiz

5. What is the total tolerance for the two-place decimal inch in Example A?

 .03

Tolerance Quiz
• What is the angular tolerance in Example C?

 030’

Tolerance Quiz
• What is the total tolerance for the three-place decimal inch in Example B?

 .004

Tolerance Quiz
• What is the total tolerance for drilled holes in Example A?

+ .010

-.002

Bolt Circles
• Three or more holes are positioned around a common center
• Located angularly on a circular centerline
Bolt Circles
• Dimension of bolt circle appears
• Inside of diagonal dimension line
• With abbreviation BC after hole data
• Holes may be equally spaced
• Abbreviation EQL SP follows quantity in local note
• Divide 360 by number of holes
• One of the holes is on vertical or horizontal centerline
Bolt Circles
• Inside of diagonal dimension line
Bolt Circles
• Inside of diagonal dimension line
Bolt Circles
• With abbreviation BC after hole data-Holes may be equally spaced
• Abbreviation EQL SP follows quantity in local note
Bolt Circles
• Holes may be located coordinately
• Use only vertical or horizontal dimensions
Shim
• How thick is the shim?

.020

Shim
• Is the shim symmetrical?

No

Shim
• Are the bolt circles concentric?

Yes

Shim
• How many holes are in the shim?

8

Shim
• What is the tolerance on the .250 Dia. holes?

.005

Shim
• What is the tolerance on the .500 Dia. holes?

.008

Shim
• What is the tolerance on the 1.000 Dia. hole?

.010

Shim
• What is the tolerance on the bolt circles?

.010

Shim
• What is the tolerance on the radii?

.02

Shim
• How much material is between the 5/8” hole and the nearest outside edge?

.1875

Shim
• How far apart angularly are the three .500 Dia. holes?

120°

Shim
• How far apart angularly are a .250 Dia. hole and the nearest .500 Dia. hole?

60°

Shim
• How far apart angularly are a .250 Dia. hole and the farthest .500 Dia. hole?

180°

Shim
• How far apart angularly is the 5/8” hole from the nearest ½” hole?

30°

Shim
• What is the angular tolerance for the hole locations?

±0°30’

Shim

What is the dimension for A?

1.15

Shim

What is the dimension for B?

1.125

Shim

What is the dimension for C?

.625

Shim

What is the dimension for D?

.525

Shim

What is the dimension for E?

.275

Maximum & Least Material Condition
• MMC
• Feature of size contains the maximum material within assigned tolerances
Maximum & Least Material Condition
• For a shaft
• At MMC when tolerance is added to its size dimension (.760)
• At LMC when tolerance is subtracted from it size dimension (.740)
Maximum & Least Material Condition
• Internal feature-hole-is at MMC when it is at its smallest size

Sizes are exaggerated. NTS-Not To Scale

Maximum & Least Material Condition
• Internal feature-hole-is at LMC when it is at its largest size

Sizes are exaggerated. NTS-Not To Scale

Maximum & Least Material Condition
• On any part
• All surfaces are features (they are not measurable-size)
• For LMC and MMC, the feature must have a size dimension
• Must be associated with tow opposing elements or two opposed parallel surfaces
• Must be measurable

1.005

.995

3.005

2.995

1.30

1.32

.349

.339

.30

.32

.66

.64

.905

.895

1.91

1.89

.258

.248

.370

.380

Allowance
• Minimum clearance between mating parts
• Maximum interference between mating parts
• Calculate by subtracting MMC of shaft from MMC of hole
Allowance
• When shaft’s MMC is smaller than hole’s MMC-positive allowance-clearance
• When shaft’s MMC is larger than hole’s MMC-negative allowance-interference
Allowance
• Positive or negative-allowance is always the tightest possible fit between mating parts
Allowance

Use the formula for calculating allowance:

MMC Hole - MMC Shaft = Allowance

Allowance

MMC Hole =.999

-MMC Shaft A =.998

Allowance =.001 (positive)

Allowance

MMC Hole =.999

-MMC Shaft B =1.004

Allowance =-.005 (negative)

Arcs And Circles
• When an arc is less than a complete circle-dimension it by radius
• May have a definite center-e.g.. 1.00R & 4.50R in Dwg. 11A004
• May float-run tangent with other arcs or lines-e.g. .75R same print
Arcs And Circles
• Radial dimension not used for circles or diameters
• Radial dimension doubles permit greater variation
Arcs And Circles
• E.g. 1.000 DIA with .01 yields dimension between .99 and 1.01 DIA
• .50R with .01 would permit diametric dimensions between .98 and 1.02 DIA
Arcs And Circles
• Is the print drawn to (a) half-size or (b) twice-size?

(a) half-size

Arcs And Circles
• What is the thickness of the spacer?

.500

Arcs And Circles
• Interpret the abbreviation CRS used in the title block?

Cold-Rolled Steel

Arcs And Circles
• How many holes does the spacer contain?

10

Arcs And Circles
• Is the spacer symmetrical about the vertical and horizontal centerline?

Vertical

Arcs And Circles
• What is the angular dimension between each small hole?

60

Arcs And Circles
• What is the angular dimension between each large hole?

120

Arcs And Circles
• What tolerance is assigned to the angular spacing of the drilled holes?

 030’

Arcs And Circles
• What is the tolerance on the bolt circles?

 .01

Arcs And Circles
• What is the tolerance on the center hole diameter?

 .005

Arcs And Circles
• What is the MMC of the center hole?

4.995

Arcs And Circles
• What is the tolerance on the drilled holes?

+.010

-.002

Arcs And Circles
• What is the MMC of the .688 holes?

.686

Arcs And Circles
• What is the overall dimension along the horizontal CL?

9.00

Arcs And Circles
• What is the overall dimension along the vertical CL?

10.50

Arcs And Circles

Enter the dimension for the letter “A.”

.50

Arcs And Circles

Enter the dimension for the letter “B.”

.531

Arcs And Circles

Enter the dimension for the letter “C.”

1.00

Arcs And Circles

Enter the dimension for the letter “D.”

.656

Arcs And Circles

Enter the dimension for the letter “E.”

.687

Arcs And Circles

Enter the dimension for the letter “A.”

.81

Arcs And Circles

Enter the dimension for the letter “B.”

2.32

Arcs And Circles

Enter the dimension for the letter “C.”

.15

Arcs And Circles

Enter the dimension for the letter “D.”

3.28

Arcs And Circles

Enter the dimension for the letter “E.”

7.26

Arcs And Circles

Enter the dimension for the letter “F.”

1.72

Arcs And Circles

Enter the dimension for the letter “G.”

1.58

Arcs And Circles

Enter the dimension for the letter “H.”

.42

Arcs And Circles

Enter the dimension for the letter “I.”

30°

Arcs And Circles

Enter the dimension for the letter “J.”

3.98

Arcs And Circles

Enter the dimension for the letter “K.”

.01

Arcs And Circles

Enter the dimension for the letter “L.”

.20

Arcs And Circles

Enter the dimension for the letter “M.”

.19

Arcs And Circles

Enter the dimension for the letter “N.”

.12

Arcs And Circles

Enter the dimension for the letter “0.”

.30

Arcs And Circles
• How much material remains between a .250 hole and the outside edge?

.225

Arcs And Circles
• How much material remains between a .220 hole and the outside edge?

.19

Arcs And Circles
• Are the .200 holes located in the exact center between ID and OD? (Calculate this.)

No

Arcs And Circles
• What is the MMC of the center hole?

2.555

Arcs And Circles
• What is the MMC of the .250 holes?

.248