Millwright Certification Blueprint Reading 2 — Questions and Answers

Question 1: On a mechanical drawing, what does a centerline (alternating long and short dashes) through a circular feature indicate?

A cutting plane
The axis of symmetry for the feature (Correct answer)
A hidden edge
A break line

Correct answer: The axis of symmetry for the feature

Centerlines show the axis of symmetry for circular features like holes, shafts, and bores, and are essential for dimensioning and locating features.

Centerlines use an alternating long-dash, short-dash pattern and indicate the geometric center or axis of circular and symmetrical features. They serve as reference points for dimensioning, such as bolt circle diameters and hole locations. Centerlines extend slightly beyond the feature outline and cross at the center point. They are distinct from hidden lines (short dashes only), cutting planes (thick with arrows), and break lines (zigzag).

Question 2: What does the welding symbol designation 'E7018' tell a millwright about the electrode?

It is for TIG welding with 70 PSI gas
It has 70,000 PSI tensile strength, all-position, low-hydrogen (Correct answer)
It is a 70mm diameter electrode for flat position only
It requires 18 volts for proper arc

Correct answer: It has 70,000 PSI tensile strength, all-position, low-hydrogen

In E7018: E=electrode, 70=70,000 PSI minimum tensile strength, 1=all-position capability, 8=low-hydrogen potassium with iron powder coating and AC/DC current.

AWS electrode classification for SMAW follows a standard numbering system. E7018 breaks down as: E (electrode), 70 (70,000 PSI or 480 MPa minimum tensile strength), 1 (usable in all positions: flat, horizontal, vertical, overhead), 8 (low-hydrogen potassium coating with iron powder, suitable for AC or DCEP). E7018 is the most commonly specified electrode for structural and industrial millwright work because its low-hydrogen properties resist cracking in medium and high carbon steels.

Question 3: In GD&T, what does the position tolerance symbol (a crosshair within a circle) control?

The surface finish of a feature
The location of a feature relative to datum references (Correct answer)
The roundness of a cylindrical surface
The straightness of an edge

Correct answer: The location of a feature relative to datum references

The position tolerance controls how far a feature's actual center may deviate from its true (theoretically exact) position relative to specified datum references.

Position is the most commonly used GD&T tolerance. It defines a tolerance zone (usually cylindrical for holes) within which the actual axis of a feature must lie. The true position is established by basic (boxed) dimensions from datum features. For example, a hole with a position tolerance of 0.25 mm diameter at MMC means the hole center must fall within a 0.25 mm diameter cylinder centered at the theoretically exact location. This replaces the older bilateral coordinate tolerancing method.

Question 4: What information does a section view on a mechanical drawing provide that a standard view cannot?

The weight of the part
Internal features and material thickness revealed by an imaginary cut (Correct answer)
The color of the materials used
Electrical wiring routing

Correct answer: Internal features and material thickness revealed by an imaginary cut

Section views show the internal structure of a part by depicting it as if cut along a plane, revealing hidden features, wall thicknesses, and internal passages that would otherwise be shown as hidden lines.

Section views are created by passing an imaginary cutting plane through a part and removing the material in front. The exposed cut surface is shown with section lining (cross-hatching) to indicate solid material. This technique is invaluable for complex parts where numerous hidden lines would make the drawing unreadable. Common types include full sections, half sections, offset sections (cutting plane changes direction), and removed sections. The cutting plane line on the parent view shows where the cut is made.

Question 5: A dimension on a drawing reads '25.00 plus or minus 0.05'. What is the total tolerance range for this dimension?

0.05 mm
0.10 mm (Correct answer)
25.05 mm
24.95 mm

Correct answer: 0.10 mm

The bilateral tolerance of plus or minus 0.05 means the acceptable range is from 24.95 to 25.05, giving a total tolerance range of 0.10 mm.

Bilateral tolerances allow variation in both directions from the nominal dimension. Here, the part may be as large as 25.05 mm (25.00 + 0.05) or as small as 24.95 mm (25.00 - 0.05). The total tolerance is the difference between the maximum and minimum limits: 25.05 - 24.95 = 0.10 mm. Understanding tolerance stacking is critical for millwrights when fitting multiple components together, as individual tolerances accumulate and can affect assembly fit.

Question 6: On an assembly drawing, what does a bill of materials (BOM) provide?

Step-by-step assembly instructions
A list of all parts with quantities, part numbers, and descriptions (Correct answer)
The cost breakdown for the project
Maintenance schedules for the assembly

Correct answer: A list of all parts with quantities, part numbers, and descriptions

A bill of materials lists every component in the assembly including item numbers, part numbers, descriptions, material specifications, and required quantities.

The BOM (bill of materials) is typically shown as a table on the assembly drawing, often above or adjacent to the title block. Each item is numbered with a balloon reference on the drawing. The BOM includes: item number, part number or drawing number, description, material specification, quantity required, and sometimes vendor information. For millwrights, the BOM is essential for verifying all components are available before beginning assembly and for ordering replacement parts during maintenance.

Millwright Certification Blueprint Reading 2

On a mechanical drawing, what does a centerline (alternating long and short dashes) through a circular feature indicate?