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ASME GDTP Technologist study materials
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ASME GDTP Technologist practice questions

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Question 1Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

Which of the following is classified as a form tolerance?

  1. Perpendicularity
  2. Profile of a surface
  3. Position
  4. Flatness Correct answer.

Explanation

Form tolerances - straightness, flatness, circularity, and cylindricity - control the shape of a feature and never reference a datum. Flatness is purely a form control. Perpendicularity and position require datums, and profile of a surface belongs to its own separate category.

Question 2Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

Which symbol indicates that a geometric tolerance applies at maximum material condition?

  1. A circled S
  2. A circled F
  3. A circled M Correct answer.
  4. A circled L

Explanation

The circled M denotes maximum material condition, the condition in which a feature contains the greatest amount of material, such as the smallest hole or the largest pin. It is placed after the tolerance value or after a datum reference to show that the tolerance or datum applies at MMC.

Question 3Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A dimension shown inside a rectangular frame is a basic dimension and represents:

  1. A theoretically exact value with no tolerance of its own Correct answer.
  2. A value that the geometric tolerance may vary
  3. A value inspected only when a note so requires
  4. A value that carries the drawing's general tolerance block

Explanation

A basic dimension is a theoretically exact value enclosed in a rectangular frame. It carries no tolerance of its own; the permissible variation comes from the geometric tolerance that references it, such as position, profile, or angularity.

Question 4Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

In a feature control frame, the datum reference letters are placed:

  1. inside the tolerance compartment, before the tolerance value
  2. in compartments to the right of the tolerance compartment Correct answer.
  3. directly above the geometric characteristic symbol
  4. in a compartment to the left of the geometric symbol

Explanation

A feature control frame is read left to right: geometric characteristic symbol, then the tolerance compartment with its value and any modifiers, then the datum references in order of precedence. Datum letters therefore occupy the compartments to the right of the tolerance compartment.

Question 5Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A feature control frame lists datum references A, B, and C in that order. Which datum establishes the primary datum plane?

  1. Datum A Correct answer.
  2. Datum C
  3. Whichever datum contacts the largest area
  4. Datum B

Explanation

Datum references are entered in order of precedence, so the first datum listed is primary, the second is secondary, and the third is tertiary. In a frame listing A, B, C, datum A establishes the primary datum.

Question 6Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A position tolerance applied to a hole is preceded by a diameter symbol. The resulting tolerance zone is:

  1. a cylinder whose axis is at the true position Correct answer.
  2. two concentric circles centered on the true position
  3. a spherical zone centered on the true position
  4. two parallel planes spaced apart by the tolerance

Explanation

When a position tolerance is preceded by a diameter symbol, the tolerance zone is a cylinder whose axis lies at the true position of the controlled axis. Without the diameter symbol the zone would be bounded by parallel planes or lines.

Question 7Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

The circled F modifier placed after a tolerance means that the tolerance applies:

  1. only when the feature is at its least material condition
  2. to a full 360 degree section of the feature
  3. with the part in its free, unrestrained condition Correct answer.
  4. only to the finished surface after coating

Explanation

The free state modifier applies to non-rigid parts and states that the tolerance applies with the part free of any restraining forces. It is commonly applied to parts such as thin rings, seals, and flexible stampings.

Question 8Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

The datum feature symbol on a drawing consists of:

  1. a letter in a rectangular frame placed inside the feature control frame
  2. a circled letter connected by a leader to the feature
  3. a letter in a frame attached to a triangle on the feature Correct answer.
  4. a letter enclosed in a hexagon placed on the feature

Explanation

A datum feature symbol is a letter in a rectangular frame joined to a filled triangle that is attached to the datum feature or its extension line. The letter identifies the datum that the feature establishes.

Question 9Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

Under Rule #1, the envelope principle, the limits of size of a regular feature of size also:

  1. apply only when a straightness tolerance is also specified
  2. limit the form of the feature at MMC Correct answer.
  3. control the location of the feature relative to the referenced datums
  4. eliminate the need for any geometric tolerance on the feature

Explanation

Rule #1 requires that the limits of size also limit form variation, so the feature may not violate an envelope of perfect form at MMC. A shaft, for example, may not be bowed or lobed enough to exceed its MMC envelope even though every local size is within limits.

Question 10Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A pin is dimensioned 10.0 to 10.4 and carries a position tolerance of 0.2 at MMC. Its virtual condition size is:

  1. 10.4
  2. 10.6 Correct answer.
  3. 10.0
  4. 10.2

Explanation

Virtual condition for an external feature is its MMC size plus the geometric tolerance that applies at MMC. Here 10.4 + 0.2 = 10.6, which is the boundary a mating part or gage must clear.

Question 11Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A hole is dimensioned 8.0 to 8.3 and has a position tolerance of 0.1 at MMC. If the hole is produced at 8.2, the total position tolerance available is:

  1. 0.3 Correct answer.
  2. 0.1
  3. 0.4
  4. 0.2

Explanation

The stated tolerance applies at MMC, which for an internal feature is 8.0. Departure from MMC is added as bonus tolerance, so 8.2 - 8.0 = 0.2 is added to the stated 0.1, giving 0.3 total.

Question 12Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

When no other indication is given, a profile of a surface tolerance zone is:

  1. unilateral, entirely outside the true profile
  2. bilateral and equally disposed about the true profile Correct answer.
  3. unilateral, entirely inside the true profile
  4. bilateral but with a larger portion outside the true profile

Explanation

Unless a unilateral or unequal disposition is specified, the profile tolerance zone is bilateral and equally disposed about the true profile. Each side of the true profile therefore receives half of the stated tolerance.

Question 13Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

Total runout differs from circular runout in that total runout:

  1. applies only at individual cross-sections taken along the axis
  2. may be used only on features referenced at MMC
  3. controls only the form of the surface, not its orientation
  4. applies to the entire surface at once as the part rotates Correct answer.

Explanation

Circular runout is checked at individual cross-sections while the part rotates. Total runout is checked over the full surface at once with the indicator traversed along the surface, so it also limits taper and other variation along the length of the feature.

Question 14Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

Angularity controls:

  1. the form of an angled surface without reference to a datum
  2. the location of a feature relative to a datum at a basic angle
  3. the size of an angled feature
  4. the orientation of a feature at a basic angle to a datum Correct answer.

Explanation

Angularity is an orientation control that limits variation of a surface, axis, or center plane from a basic angle measured relative to a datum. It does not limit size, and it cannot be applied without a datum.

Question 15Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A straightness tolerance applied to a feature of size rather than to its surface controls:

  1. the flatness of the feature's end faces
  2. the perpendicularity of the feature axis to its primary datum
  3. the circularity of each cross-section of the feature
  4. the derived median line of the feature Correct answer.

Explanation

Straightness applied to a feature of size controls the derived median line rather than the surface elements. When it is specified at MMC it establishes a boundary the median line must stay within, and the allowable straightness grows as the feature departs from MMC.

Question 16Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A projected tolerance zone is used mainly to:

  1. permit a part to be inspected in the free state
  2. control the depth of a blind hole
  3. allow the tolerance to grow as the hole departs from MMC
  4. control the hole axis over the thickness of the mating part Correct answer.

Explanation

A projected tolerance zone extends the tolerance zone beyond the feature by a stated distance, usually representing the thickness of the mating part. This prevents a hole that is oriented within tolerance over its own length from causing interference with a fastener or pin during assembly.

Question 17Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A datum feature simulator is:

  1. a gage pin used only for inspection of position at MMC
  2. the surface of perfect form that establishes the datum Correct answer.
  3. the actual datum feature surface as produced
  4. the origin point of the datum reference frame

Explanation

The datum feature simulator is the surface of perfect form, such as a surface plate, chuck, or gage element, that contacts the datum feature and establishes the datum. The datum is derived from the simulator, not from the imperfect produced surface itself.

Question 18Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

The continuous feature symbol indicates that:

  1. the tolerance applies around the entire profile of the part
  2. interrupted features in line are treated as one feature Correct answer.
  3. the feature may be produced in more than one operation without inspection
  4. the feature continues from one part to its mating part

Explanation

The continuous feature symbol tells the reader that interrupted features, such as a bearing journal broken by a groove, are to be treated as a single feature of size. Size limits and geometric controls then apply to the interrupted feature as a whole.

Question 19Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A profile of a surface tolerance of 0.6 with a U modifier value of 0.2 means that:

  1. the zone is 0.2 in total and is bilateral
  2. 0.4 of the zone lies outside the true profile and 0.2 inside
  3. the zone is 0.6 outside the true profile and 0.2 inside
  4. 0.2 of the zone lies outside the true profile and 0.4 inside Correct answer.

Explanation

The U modifier makes an otherwise bilateral profile tolerance unequal. The value following U is the portion of the total zone lying outside the true profile, so a 0.6 total with U 0.2 gives 0.2 outside and 0.4 inside.

Question 20Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

The tangent plane modifier specifies that:

  1. the tolerance applies to the low points of the surface
  2. the surface must be perfectly flat
  3. the tolerance applies to a plane tangent to the high points Correct answer.
  4. the feature must be inspected with a CMM rather than a hard gage

Explanation

The tangent plane modifier means the tolerance applies to a plane tangent to the high points of the surface rather than to every point on the surface. It is used where only contact with a mating plane matters, such as a sealing or mounting surface.

Question 21Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

In a composite position tolerance, the lower segment of the frame:

  1. controls the orientation and spacing of the pattern features Correct answer.
  2. controls the location of the pattern as a group within the larger zone
  3. always permits the pattern to rotate freely relative to the datums
  4. replaces the upper segment when the pattern is produced at MMC

Explanation

A composite position frame has two segments. The upper segment locates the pattern as a group relative to the datums, while the lower segment controls only the orientation and spacing of the features within the pattern, so the pattern may still shift as a group within the larger zone.

Question 22Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A hole of size 6.0 to 6.2 is given a zero position tolerance at MMC. This means:

  1. the position tolerance grows from zero as the hole departs from MMC Correct answer.
  2. the position requirement is met only if the hole is produced at its MMC size
  3. no position tolerance exists and the hole must be perfectly located at every size
  4. the hole may deviate in location by its size tolerance only when produced at LMC

Explanation

A zero positional tolerance at MMC is a legal callout stating that the axis must be exactly at true position when the hole is at MMC. As the hole departs from MMC, bonus tolerance equal to the departure becomes available, so the axis may move by that amount.

Question 23Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A primary datum plane established from a datum feature simulator constrains:

  1. six degrees of freedom
  2. one degree of freedom
  3. three degrees of freedom Correct answer.
  4. two degrees of freedom

Explanation

A primary planar datum removes translation along its normal and both rotations about axes lying in the plane, for a total of three degrees of freedom. The secondary datum removes two more and the tertiary removes the last one, completing the six-degree-of-freedom datum reference frame.

Question 24Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

Referencing a datum feature of size at MMB rather than RMB:

  1. adds bonus tolerance to the geometric tolerance of the controlled feature
  2. removes the datum shift allowance and fixes the part rigidly to the datum feature simulator
  3. permits the part to shift relative to the simulator by its departure from MMB Correct answer.
  4. requires the datum feature to be produced at its MMC size

Explanation

Referencing a datum feature of size at MMB fixes the simulator at the MMB size while the actual part may float. The permitted movement equals the amount by which the datum feature departs from MMB, and this allowance is called datum shift.

Question 25Fundamentals of GD&T and Y14.5 concepts, symbols, and rules

A profile of a surface tolerance applied to a planar surface with no datum references controls:

  1. the location of the surface relative to the datums
  2. the form of the surface only Correct answer.
  3. the size of the surface only
  4. the orientation of the surface to the primary datum

Explanation

With no datum references, a profile tolerance constrains only the form of the surface relative to its true profile and is not tied to any datum reference frame. Locating or orienting the surface requires datums to be cited in the profile feature control frame.

Question 26Datum reference frames, datum features, and datum selection

In GD&T, a datum is best described as which of the following?

  1. A theoretically exact plane, axis, or point used as a reference Correct answer.
  2. The maximum allowable variation of a surface from its basic location
  3. The boundary of the tolerance zone stated in the feature control frame
  4. A physical surface of the part that contacts the inspection equipment during measurement

Explanation

A datum is a theoretical reference, such as a plane, axis, point, or combination of these, from which the location and orientation of features are established. It has no size and no error. The real part surface that touches the equipment is the datum feature, and the equipment itself is the datum feature simulator.

Question 27Datum reference frames, datum features, and datum selection

Which statement correctly distinguishes a datum feature from a datum?

  1. The datum feature is a theoretical construction and the datum is the real surface it represents on the part
  2. Both terms describe the same physical surface on the drawing and may be used interchangeably
  3. The datum feature is the real part feature used to establish the theoretical datum Correct answer.
  4. The datum feature is the inspection fixture and the datum is the gage pin that enters the hole

Explanation

The datum feature is the actual feature on the part, such as a face or a hole, that is selected to establish a datum. The datum itself is the theoretical plane or axis derived from that feature by the datum feature simulator.

Question 28Datum reference frames, datum features, and datum selection

How many degrees of freedom must a complete datum reference frame remove from a rigid part?

  1. Four
  2. Twelve
  3. Six Correct answer.
  4. Three

Explanation

A free rigid body has six degrees of freedom: three translations along the axes and three rotations about them. A complete datum reference frame removes all six so that every feature is fully located and oriented for measurement.

Question 29Datum reference frames, datum features, and datum selection

A flat primary datum feature is brought into contact with a surface plate. What is the minimum number of contact points that establishes the primary datum plane?

  1. One
  2. Four
  3. Three Correct answer.
  4. Two

Explanation

A plane is defined by three non-collinear points, so the primary simulator contacts the high points of the datum feature at a minimum of three locations. Additional contact may occur, but at least three points are needed to seat the part and establish the plane.

Question 30Datum reference frames, datum features, and datum selection

A datum reference frame is normally made up of which of the following?

  1. Three mutually perpendicular planes that intersect at the origin Correct answer.
  2. Two parallel planes separated by the size of the datum feature
  3. Three planes that may be oriented at any angle to one another, as drawn on the part
  4. One plane plus the axis of the largest hole on the part

Explanation

The datum reference frame consists of three mutually perpendicular planes that intersect at a common origin. Measurements and tolerance zones are oriented and located from these planes.

Question 31Datum reference frames, datum features, and datum selection

How is the precedence of datum features determined in a feature control frame?

  1. By the size of the tolerance stated in the feature control frame
  2. By reading the datum letters from left to right Correct answer.
  3. By the alphabetical order of the datum letters
  4. By the physical size of the datum features on the part

Explanation

The datum letters are read left to right, and that order sets precedence. The leftmost letter is the primary datum, the next is secondary, and the last is tertiary. The letters themselves need not be alphabetical.

Question 32Datum reference frames, datum features, and datum selection

A position tolerance is shown as |POS|DIA 0.25|C|A|B|. Which datum feature is primary?

  1. B
  2. C Correct answer.
  3. A
  4. The datum tied to the size dimension of the hole

Explanation

The first datum letter after the tolerance block is the primary datum. Here C appears first, so C is primary, A is secondary, and B is tertiary, regardless of the alphabetical order of the letters.

Question 33Datum reference frames, datum features, and datum selection

In a datum reference frame established by three mutually perpendicular planes, the tertiary datum plane removes which remaining freedom?

  1. Two rotational degrees of freedom
  2. One translational degree of freedom Correct answer.
  3. Three translational degrees of freedom
  4. One rotational degree of freedom

Explanation

For a three-plane frame, the primary removes three degrees of freedom (one translation and two rotations) and the secondary removes two more. Only one translation remains, and the tertiary plane removes it.

Question 34Datum reference frames, datum features, and datum selection

What is a datum feature simulator?

  1. A CAD model of the datum feature used to program the coordinate measuring machine
  2. The tolerance zone within which the datum feature must lie
  3. A precise surface that contacts the datum feature to establish the datum Correct answer.
  4. The actual part surface that contacts the inspection equipment

Explanation

The datum feature simulator is a surface of adequately precise form, such as a surface plate, mandrel, chuck, or gage pin, that contacts the datum feature and establishes the theoretical datum. Examples include a surface plate for a flat face and an expanding mandrel for a hole.

Question 35Datum reference frames, datum features, and datum selection

A long cylindrical feature is designated as the primary datum. How many degrees of freedom does its datum axis remove?

  1. Six
  2. Two
  3. Three
  4. Four Correct answer.

Explanation

A primary datum axis prevents translation in two directions and rotation about two axes perpendicular to it. That leaves only translation along the axis and rotation about the axis, so four degrees of freedom are removed.

Question 36Datum reference frames, datum features, and datum selection

A hole is referenced as the primary datum at RMB. The datum axis is the axis of which of the following?

  1. The largest inscribed cylinder that contacts the hole surface Correct answer.
  2. The cylinder at the hole's least material condition size
  3. The cylinder at the hole's maximum material condition size
  4. The smallest circumscribed cylinder that contacts the hole surface

Explanation

At RMB the simulator expands inside the hole until it contacts the surface, producing the unrelated actual mating envelope. For an internal feature this envelope is the largest inscribed cylinder, and its axis is the datum axis.

Question 37Datum reference frames, datum features, and datum selection

In a feature control frame, a circled M following a datum letter, such as B with a circled M, means which of the following?

  1. The datum feature must be produced at its maximum material condition to be accepted
  2. The datum feature simulator is fixed at the datum feature's virtual condition Correct answer.
  3. The datum applies only when the toleranced feature is at maximum material condition
  4. The size tolerance of the datum feature is removed from the drawing requirement

Explanation

The circled M after a datum letter specifies the maximum material boundary for that datum feature. The simulator is a fixed boundary equal to the datum feature's virtual condition, and the datum feature may shift within the available clearance.

Question 38Datum reference frames, datum features, and datum selection

A hole is referenced as a datum feature at MMB, and the hole is produced larger than its virtual condition. What is the outcome?

  1. The part is rejected because the datum feature exceeds its virtual condition
  2. The datum reference frame is no longer valid for the part
  3. Datum feature shift is permitted, so the part may shift relative to the simulator Correct answer.
  4. The position tolerance of the toleranced feature is increased by the shift amount

Explanation

At MMB the simulator is fixed at virtual condition, so any clearance between the actual mating envelope of the hole and the simulator may be used as datum feature shift. The part can move within that clearance while the toleranced feature is being verified.

Question 39Datum reference frames, datum features, and datum selection

Datum targets are most appropriate in which situation?

  1. When the datum feature is irregular or full contact is impractical Correct answer.
  2. When the datum feature is a clearance hole used for assembly
  3. When the designer wants to eliminate the datum reference frame
  4. When a flat, machined datum feature makes full contact with a surface plate during inspection

Explanation

Datum targets are designated points, lines, or areas used when a datum feature cannot be contacted reliably over its whole extent, as with cast, forged, or warped surfaces. They make the established datum repeatable from part to part and between design and inspection.

Question 40Datum reference frames, datum features, and datum selection

Two coaxial holes are identified as datum features A and B and referenced together as A-B. What does this mean?

  1. Both features together establish one common datum axis Correct answer.
  2. A is primary and B is secondary, in that order
  3. The datum axis is located midway between A and B only if both are at MMC
  4. Either A or B may be used, whichever is more convenient for inspection

Explanation

A-B is a compound datum. The two features are used simultaneously to establish a single common datum axis, and neither feature alone establishes the datum.

Question 41Datum reference frames, datum features, and datum selection

A machined rectangular bracket has a large flat mounting base, a long machined side face, and a short machined end face. Which is normally selected as the primary datum feature?

  1. The short end face, because it is the easiest surface to machine
  2. The face carrying the tightest size tolerance on the drawing
  3. The long side face, because it is the longest machined surface on the part
  4. The large flat mounting base, because it gives stable functional support Correct answer.

Explanation

The primary datum should be the functional mating surface that seats the part most stably, which is usually the largest and flattest face. Secondary and tertiary datums then remove the remaining freedom.

Question 42Datum reference frames, datum features, and datum selection

A cast surface with significant waviness is designated as the primary datum without datum targets. What is the main consequence during inspection?

  1. The datum plane passes through the average of the surface's high and low points
  2. The datum plane is established at the lowest point of the surface
  3. The datum rests on the high points, so it may rock Correct answer.
  4. The surface is automatically rejected by the datum requirement

Explanation

A simulator contacts only the high points of a datum feature, so a wavy surface can seat differently from one setup to the next. The resulting datum reference frame is not repeatable, which is why datum targets or a form control on the datum feature are used.

Question 43Datum reference frames, datum features, and datum selection

What does the datum translation modifier, shown as a circled T after a datum letter, permit?

  1. The datum feature may translate within its size tolerance
  2. The toleranced feature may translate within its tolerance zone
  3. The simulator of a datum feature of size may translate from its basic location Correct answer.
  4. The datum reference frame may rotate about the primary datum

Explanation

The translation modifier allows the datum feature simulator of a datum feature of size to translate away from its basic location. It is applied where the location of that datum feature is not constrained by higher-precedence datums.

Question 44Datum reference frames, datum features, and datum selection

After the primary datum (a flat face) and the secondary datum (a hole perpendicular to that face) are established, which freedom remains that a tertiary datum must remove?

  1. Translation normal to the primary plane
  2. Tipping of the primary plane off the surface plate
  3. Rotation about the axis of the secondary hole Correct answer.
  4. Translation along the axis of the secondary hole

Explanation

The primary plane removes translation normal to it and two rotations, and the secondary hole removes the two translations in the plane. Only rotation about the hole axis remains, so a tertiary feature such as a slot or second hole clocks the part.

Question 45Datum reference frames, datum features, and datum selection

A functional gage is built to verify a position tolerance referenced to |A|B|C|. How must the gage simulators be arranged?

  1. With each simulator sized at the least material condition of its datum feature
  2. To contact only primary datum A and the toleranced feature
  3. To contact A, B, and C in the same precedence as the feature control frame Correct answer.
  4. In any order, as long as all three datum features are contacted

Explanation

The gage must reproduce the datum reference frame of the feature control frame. The simulators contact the datum features simultaneously in the stated precedence, and their sizes follow the applicable boundary, such as MMB, LMB, or RMB.

Question 46Datum reference frames, datum features, and datum selection

A hole datum feature B is toleranced DIA 10.0-10.2 and is controlled by a position tolerance of DIA 0.2 to datum A. B is referenced as a datum at MMB. What pin size establishes the datum feature simulator for B?

  1. DIA 9.8 Correct answer.
  2. DIA 10.2
  3. DIA 10.4
  4. DIA 10.0

Explanation

For an internal datum feature at MMB, the simulator is fixed at the virtual condition, which is the MMC size minus the geometric tolerance: 10.0 minus 0.2 equals 9.8. The pin of that size defines the boundary within which the datum feature may shift.

Question 47Datum reference frames, datum features, and datum selection

A flat face is primary datum A and a hole is secondary datum B. The hole is drilled slightly out of square with A. Which statement about datum axis B is correct?

  1. Datum axis B follows the axis of the hole as produced on the part
  2. The part must be rejected because the hole is not square to A
  3. Datum axis B is tilted from perpendicular by the amount of the squareness error
  4. Datum axis B is perpendicular to A because its simulator is normal to A Correct answer.

Explanation

In a datum sequence, each simulator is oriented by the higher-precedence datums. The secondary simulator is therefore normal to datum plane A, and the part is adjusted until the hole contacts it, so the datum axis is the simulator axis and is perpendicular to A regardless of the hole's as-produced tilt.

Question 48Datum reference frames, datum features, and datum selection

A shaft rotates in two bearings that are separated along its length. Which datum scheme best reflects the function of the part?

  1. The large end face as the primary datum
  2. The two bearing journals as a common datum establishing one axis Correct answer.
  3. The largest diameter as the primary datum
  4. The keyway as the primary datum

Explanation

Datum features should be the surfaces that functionally locate the part in assembly. In service the two bearing journals locate the shaft axis, so using them together as a compound datum produces a datum axis that matches the function and the mating conditions.

Question 49Datum reference frames, datum features, and datum selection

Where is the origin of a datum reference frame located?

  1. At the intersection of the datum planes set by the simulators Correct answer.
  2. At the point on the datum feature closest to the toleranced feature
  3. At the center of the largest feature on the part
  4. At the centroid of the part's volume

Explanation

The datum planes are established by the datum feature simulators in contact with the datum features, and the datum reference frame origin is their intersection. It is a theoretical point that does not depend on the part's mass properties or feature sizes.

Question 50Datum reference frames, datum features, and datum selection

A hole is position toleranced with reference to |A|B| only, where A is a flat face and B is a hole perpendicular to A. What is the effect of omitting a tertiary datum?

  1. The position tolerance zone is not located relative to datum B
  2. The position tolerance must be changed to a profile tolerance
  3. The tolerance zone may rotate about datum axis B, so clocking is not controlled Correct answer.
  4. The position tolerance zone is not oriented to datum A

Explanation

With only a primary plane and a secondary axis, rotation about that axis remains unconstrained. The tolerance zone can therefore rotate about datum axis B, so rotational location of the feature is not controlled until a tertiary datum is added.