CNC Blueprint Reading & Technical Drawing Interpretation 2 — Questions and Answers
Question 1: On a technical drawing, what does a hidden line (dashed line) represent?
- A surface that is visible from the current view
- An edge or feature not visible from the current viewing direction (Correct answer)
- A centerline for a hole or axis
- A cutting plane for a section view
Correct answer: An edge or feature not visible from the current viewing direction
Hidden lines are dashed and indicate edges or features that exist behind or inside the part as viewed from that projection direction.
Question 2: A GD&T feature control frame reads ⊙ | 0.005 | A | B. What does the ⊙ symbol indicate?
- Flatness
- Cylindricity
- Position (Correct answer)
- True position
Correct answer: Position
The circle with a cross (⊙) is the GD&T symbol for Position, controlling the location of a feature relative to datums.
Question 3: What is the purpose of a revision block on an engineering drawing?
- To list all tolerances used on the drawing
- To document changes made to the drawing after initial release (Correct answer)
- To identify the material specification
- To show the scale of the drawing
Correct answer: To document changes made to the drawing after initial release
The revision block tracks all engineering change orders (ECOs), recording the revision letter, description, date, and approver.
Question 4: In third-angle projection (used in the US), where is the right-side view placed relative to the front view?
- To the left of the front view
- Below the front view
- To the right of the front view (Correct answer)
- Above the front view
Correct answer: To the right of the front view
In third-angle projection, the right-side view is placed to the right of the front view, matching the side from which you are looking.
Question 5: A drawing note specifies 'ALL FILLETS AND ROUNDS R.125 UNLESS OTHERWISE SPECIFIED.' What does this mean for a CNC machinist?
- All external sharp corners must be chamfered at 0.125 inches
- All unspecified internal corners and external rounded edges are 0.125-inch radius (Correct answer)
- Only holes require a 0.125-inch radius break
- The tolerance on all dimensions is ±0.125
Correct answer: All unspecified internal corners and external rounded edges are 0.125-inch radius
This general note sets a default radius for all unspecified internal fillets and external rounds, saving space on the drawing.
Question 6: What does the term 'true profile' refer to in GD&T profile tolerances?
- The actual measured shape of a machined surface
- The theoretically exact geometry of a surface as defined by basic dimensions (Correct answer)
- The maximum material condition of a surface
- The surface finish required on a complex contour
Correct answer: The theoretically exact geometry of a surface as defined by basic dimensions
True profile is the perfect theoretical geometry defined by basic (boxed) dimensions that the profile tolerance zone is centered on.
Question 7: On a CNC blueprint, a dimension shown as 1.500 ± 0.005 means the feature must be between what values?
- 1.490 and 1.510
- 1.495 and 1.505 (Correct answer)
- 1.500 and 1.505
- 1.495 and 1.500
Correct answer: 1.495 and 1.505
Adding and subtracting 0.005 from 1.500 gives a range of 1.495 (minimum) to 1.505 (maximum).
CNC Blueprint Reading & Technical Drawing Interpretation 2
On a technical drawing, what does a hidden line (dashed line) represent?