This unit will focus on selected fundamental symbols and terms for reading geometric dimensioning and tol­erancing (GDT) drawings. The content is limited to the extent that is required for reading foldout drawing #8, Roller Stand Weldment. Additional study will be necessary for reading more complex drawings. Geometric dimensioning and tolerancing is the most current standard for dimensioning orthographic drawings. The majority of manufacturing companies, including the military, have adopted this standard. There are similarities between the coordinate and GDT standards; however, GDT incorporates the use of special geometric symbols, modifiers, and terms not found on coordinate dimensioned drawings. A listing of the most common symbols in GDT dimensioning is found in Figure 28.1. These are identified as Geometric Characteristic Symbols. In addition to geometric symbols, a set of symbols identified as Geometric Symbol Modifiers are used in conjunction with geometric characteristic symbols, Figure 28.2.

CHARACTERISTIC	SYMBOL
FLATNESS	EJ
STRAIGHTNESS	—
CIRCULARITY	о
CYLINDRICITY	о
PERPENDICULARITY	_L
ANGULARITY	Z
PARALLELISM	//
POSITION
CONCENTRICITY	О
CIRCULAR RUNOUT	X
TOTAL RUNOUT	AS
PROFILE OF A LINE	/-л
PROFILE OF A SURFACE

FIGURE 28.1 ■ Geometric characteristic symbols.

TERM	SYMBOL
DIAMETER	0
SPHERICAL DIA	S0
MAXIMUM MATERIAL COND
LEAST MATERIAL COND	©
PROJECTED TOLERANCE ZONE	©
FREE STATE	©
TANGENT PLANE	©
STATISTICAL TOLERANCE	<"sD
REGARDLESS OF FEATURE SIZE	©

FIGURE 28.2 ■ Geometric modifier symbols.

Feature control frames are used to contain geometric characteristic symbols, geometric symbol modifiers, and other special symbols related to GDT dimensioning. Typical feature control frames with geometric char­acteristic symbols are illustrated in Figure 28.3 and Figure 28.4.

The first item contained within a feature control frame is always a geometric characteristic symbol. Not more than one such symbol is shown within a frame, Figure 28.3. The number and size of compartments within a frame will vary depending upon the extent of data to be specified. Also, any additional data to be included in the compartments that follow are shown in accordance with a national standard that specifies the sequence to be followed.

<

>

_L

О

FIGURE 28.3 ■ Examples of feature control frames.

When required, a geometric symbol modifier is the second item included in a feature control frame. It refers to the geometric characteristic symbol that precedes it. Note: Modifiers are not used for the following geometric characteristic symbols:

Straightness---------

Flatness

Circularity

Cylindricity

In such cases, the second item shown in the frame is a tolerance value. Geometric characteristic symbols requiring the use of a modifier are as follows:

profile of a surface . . J±s position concentricity symmetry -=

perpendicularity _|_ parallelism //

circular runout /

total runout U profile of a line

Figure 28.4 illustrates examples of data contained within a feature control frame with the proper sequence of data. Note that all dimensions using Feature Control Frames are in decimal fractions. This also applies to all dimensions shown in a GDT drawing, with some exceptions. For example, size dimensions for welding symbols are shown as common fractions as well as dimensions for stock items such as steel angle: 21,/) X 2V2 X 3/ie.

The basic sequence of items in a feature control frame is also illustrated in Figure 28.5. Other items may be added to the frame for special purposes; however, they are not included in this abbreviated study

At this point, it is important to understand the concept of a feature. There are several applications of the word “feature.” Refer to Figure 28.6.

■ Feature: a term applied to a part such as a surface, slot, or hole.

■ Feature of size: a size dimension applied to a part that may be a circle, sphere, angle, or distance between two or more parallel surfaces.

■ Feature of location: a size dimension that locates the centerlines of a circle or a centerline of a part in re­

lation to another part. Refer to Figure 28.6 for an example of each kind of feature.

■ Datum feature: any feature of a part such as a surface, plane, or hole.

Feature control frames are applied to drawing parts and dimensions in a number of ways. Figure 28.7

illustrates several examples of how frames are applied Their purpose is to refine the dimensioning of parts on a drawing in order to produce a more acceptable and economical product.

A datum feature symbol is another special symbol used in GDT drawings. This symbol is illustrated in Figure 28.8.

Note that the original symbol identified as obsolete has been replaced by a preferred (current) symbol; however, many drawings will have the obsolete symbol as shown in Figure 28.8.

FIGURE 28.5 ■ Standard sequence of items in a feature control frame.

FEATURE OF 1025 LOCATION

10.4 FEATURE 10.0 OF SIZE

FIGURE 28.6 ■ Identification of kinds of features.

DATUM FEATURE

-FEATURE OF SIZE

5.00

FEATURE OF LOCATION

FIGURE 28.8 ■ Examples of datum feature symbol locations.

PREFERRED OBSOLETE

The letter contained within a datum feature on a drawing may have reference to a surface dimension or any other feature that makes up the drawing. The datum feature symbol may be attached to an extension line or attached to a feature control frame Figure 28.9.

Another important concept to be understood for interpreting a GDT drawing is the reference to the size of an item on the drawing shown within a feature control frame—least material condition shown by the symbol (L, and maximum material condition shown by the symbol M Figure 28.10(a)

of each of these symbols. Note that least material condition (LMC) refers to a part when its material content is produced at its lower size limit, and maximum material condition (MMC) refers to the condition of a part when its material content is produced at its upper size limit.

Figure 28.10(b) is another example that illustrates the concept of maximum and least material conditions of a part. Note that when there is a hole in the part, the part is at MMC when the dimension is at its lowest limit, and at LMC when the hole is at its upper limit.

-0- 0.010 @ A

B

FIGURE 28.9 ■ Examples of locations of a datum feature symbol.

a>1

©

2 + - 8

FIGURE 28.10(a) ■ Maximum and least material conditions of a part.

MMC

FIGURE 28.10(b) ■ Additional examples of maximum and least material conditions of a part.

Other items found on GDT drawings that are also common to coordinate drawings are as follows:

■ A dimension enclosed in a square | 2.02 | is identified as a basic dimension. It is considered to be an exact dimension to which tolerance values are applied.

■ A dimension enclosed in parenthesis (3.02) is identified as a reference dimension. It is not a required dimension. However, it may be included to expedite reading a drawing without the need for addition or subtraction of dimensions to obtain a size.

■ An all-around

0~ is used to indicate the dimension that applies to all around the feature, just as a simi­lar symbol in welding indicates to weld-all-around.

■ □ symbol for indicating a square.

■ I I symbol for indicating a counterbore or spotface.

■ V symbol for indicating a countersink.

■ T symbol for indicating depth.

■ X symbol for number of places; for example, 6X.

The illustration that follows (Figure 28.11) is an example of GDT dimensioning and the interpretation of the feature control frames used.

UNIT 28: REVIEW A

Graph paper is provided at the end of this review for your use.

1. Sketch the geometric characteristic symbols for the following:

a. Parallelism

b. Circularity

c. Straightness

d. Profile of a line

e. Perpendicularity

f. Angularity

g. Flatness

2. Interpret the following symbols.

a. ©----------------------------------------------------------

b. 0-------------------------------------------------------------

c. M

d. © 0

3. Identify the geometric characteristic symbols that do not require a modifier.

4. Sketch three geometric characteristic symbols requiring a geometric symbol modifier.

5. Sketch a feature control frame symbol showing a geometric characteristic symbol with a flatness tolerance value of.020.

8. a. In the sketch that follows, identify a feature, a feature of size, a feature of location, and a datum feature.

b. Add a feature control frame to the surface indicated by an X that will indicate the flatness of a feature with a.005 tolerance value.

9. a. Complete what is missing in the following datum feature symbol.

b. Sketch the obsolete symbol for a datum feature symbol.

10. What is the significance of the following symbols with reference to GDT drawings?

6. What type of dimensioning must be used in a control frame?

7. Sketch a feature control frame symbol that includes a geometric characteristic symbol for position, a diameter symbol with a tolerance value of.015, a maximum material condition symbol, and datum reference with the letter B.

UNIT 28: REVIEW B

Note: The following questions refer to foldout drawing #8, Roller Stand Weldment

7. What is the significance of each of the feature control frames that follow?

1. List the dimension tolerances for the stand.

a. Decimal

//

A

.010

b. Fractional

c. Angular

±

.010

C

2. Give the revision record for the drawing.

8. Interpret the tolerances specified in the title box:

a. decimal ±.xx

b. decimal ±xxx

3. Sketch two reference dimensions found on the drawing that are outdated methods for indicating a reference.

4. Sketch each of the welding symbols found on the drawing and interpret each.

5. What is the significance of the following dimen­sion as shown on the symbol that follows?

c. angular ±3

9. a. What is the purpose of the breaklines shown on the print?

<2X

4

-3 -1 - 2 16 2

b. On what number part(s) are they located?

c. On which view(s) are they shown?

10. List the material required to make the weldment stand, and the number required of each.

6. List the various materials that are stock items for making the stand. Include the dimensions

for each. 11. a. What is the overall size of the weldment

stand?________________________________

b. How many welds are required?

12. a. List the size of part (06) including length. 21. a. Identify the views shown on the drawing.

b. Which of these dimension(s) is approximate?

13. a. Identify the part that revision “A” refers to.

b. Identify the locations of the broken-out enlarged detail views.

b. What was the original data specified?

c. What is the purpose of these views?

14. a. What size is specified for the steel angel part?__

b. What is the overall length required?

15. Interpret the significance of the following dimensions.

a. 3.00 Ref.

16.53

16.47

22. What are the maximum and minimum dimen­sions for the following?

a. R.750 max. min.

b. 15.25 max. min.

23. Interpret the following GDT symbols.

a. - a!

b.

B]

16. a. Sketch the welding symbols applicable to

part @.

b. Interpret each element found on these symbols.

c. Which symbol has replaced the other as the most current symbol?

24. Interpret the following GDT symbols.

//

A

D

17. What is the rectangle that encloses the GDT data referred to as?

18. What is the purpose of the following GDT symbol?

E

19. What is the size of the rectangular steel tubing component?

20. a. On what parts by number are chamfers specified?

25. a. Sketch the welding symbol for joining the part to part ^04.

b. Interpret the symbol.

32. Identify whether the print is first-angle or third - angle projection, a multiple or detail assembly print, or both a multiple detail and assembly print.

26. a. Sketch the welding symbol for joining part to part

b. Interpret the symbol.

33. Which part requires a surface finish?

27. a. Sketch the welding symbols for joining part I to part (04).

b. Interpret each welding symbol.

34. Sketch the welding symbol on the print that specifies a convex surface finish. 35. a. What is the difference between a weld symbol and a welding symbol?

28. a. Sketch the symbol for joining part (O5 to part

b. Interpret the symbol.

b. Sketch a welding symbol with multiple reference lines. c. What is the purpose of the multiple reference lines?

29. Sketch the joint configuration for welding part 04 to part (

30. a. What tolerance(s) is applicable to the R.750 dimension?

d. Are multiple reference lines applicable to any of the symbols shown on the print?

b. In how many places?

31. What is the purpose for using three arrow lines for the symbol shown on the print as follows:

36. a. What is the total length of the fillet welds required to assemble all of the pieces?

b. What is the total length of the flare-bevel weld for assembling the pieces?

UNIT 28: REVIEW C

Note: The following questions refer to foldout drawing #10, Strongback Stand.

1. What is the significance of the following symbols?

c. (10.12") 2X d. ±.12 9.00" e. (R1.015)

2x 5.00"

6X 0 .562" THRU

2. a. List the kinds of welds shown on the print.

b. Which symbol indicates an other side weld?

15. Prepare a sketch with dimensions to show the chamfers required at each end of the tubing including tolerances where applicable. 16. a. What size of steel angle material is required?

3. What radius is specified for all edges of the tubing?__________________________________ 4. What angular tolerance is specified for all chamfers?________________________________

b. How many angle pieces?

5. Identify the dimensions to which a.06 tolerance is applied.____________________________________

17. List the total length of the strongback stand.

18. What is the inside size of the tubing? Add the symbol for indicating an approximate size.

6. What tolerance is applied to the six drilled holes on the steel angle pieces?__________________________ 7. Prepare a sketch showing the location dimensions for the drilled holes on the steel angle pieces.

19. What is the spacing of the drilled holes between each end of the tubing?

20. How many inches of weld is required for each steel angle?______________________________________ 21. Sketch the shape of the joints of the steel angle to be welded. 22. a. I dentify the location of the surface(s) requir­ ing a finish.

8. What is the significance of the following

.005

A

B

9 a. Are any revisions specified on the drawing?

b. Is provision provided on the drawing to list revisions?_________________________________ 10. What is the significance of the following dimen­sion? 24.00" (REE)_________________________________

b. List the dimension(s) applicable to the finish.

23. I dentify the dimension(s) which has a + tolerance to three decimal places.__________________________

11. What is the size indicate by the following weld­ing symbol? і Г________________________

24. List the common fraction dimensions shown on the print and the items to which these toler­ances apply.

12. a. Interpret the following dimension(s). 8X .50" X 45° CHAMFER

b. 2X 0.781" THRU.

25. a. With reference to the line weight(s) used on the drawing, identify the method for producing it.___________________________________ b. Give the reason for your answer.

13. a. Prepare a simple sketch to show the location dimensions for the drilled holes in the tubing. b. What tolerance size is applicable to the drilled holes?____________________________________

14. Prepare a sketch with dimensions to show the chamfers required on the steel angles.