A/an ______ circle is a circular centre line on a drawing containing the centres of holes about a common centre.
bolt
Understanding the Bolt Circle in Technical Drawing
The question asks for the specific term used in technical drawings for a circular centre line that shows the location of centres of holes arranged around a common centre. This is a fundamental concept in engineering and technical drafting.
Let's examine the options provided:
- axis: An axis is typically a real or imaginary line about which an object rotates or is symmetrically arranged. While related to the centre, it's not the term for the circular line showing hole centres.
- bolt: The term "bolt circle" is a standard term in technical drawing. It specifically refers to the circle on which the centres of a pattern of holes (often for bolts, hence the name) are located, all sharing a common centre.
- concentric: Concentric means sharing a common centre. While the bolt circle and the pattern of holes it defines are concentric with the main centre, "concentric circle" is a general geometric term and not the specific term used in technical drawing for this feature.
- peripheral: Peripheral refers to the outer edge or boundary. A peripheral circle would be on the outside, not necessarily indicating the centres of internal features like holes.
Based on the definition given in the question – "a circular centre line on a drawing containing the centres of holes about a common centre" – the term that precisely matches this description in the context of technical drawing is a bolt circle.
Therefore, a bolt circle is the correct term.
Explanation of Bolt Circle
In technical drawings, especially for mechanical parts, you often need to show patterns of holes that are equally spaced around a central point. These holes are frequently intended for fasteners like bolts, studs, or pins. To clearly indicate the position of these holes without drawing dimension lines to each individual hole from the centre, a bolt circle is used.
Key features of a bolt circle:
- It is represented as a centre line (a dashed line alternating with long dashes).
- It is drawn concentrically with the main feature or central axis.
- It passes through the exact centres of all the holes in the pattern.
- The diameter of the bolt circle (often abbreviated as B.C.D. for Bolt Circle Diameter) is a critical dimension used to locate the holes.
Using a bolt circle simplifies dimensioning and makes the drawing easier to read and interpret for manufacturing or assembly purposes.
| Term | Definition in Drawing Context | Matches Question? |
|---|---|---|
| Axis | Line of rotation or symmetry | No |
| Bolt Circle | Circular centre line showing centres of holes about a common centre | Yes |
| Concentric Circle | Circle sharing a common centre | No (too general) |
| Peripheral Circle | Circle on the outer boundary | No |
Revision Table: Technical Drawing Terms
Here is a quick revision of related terms in technical drawing:
- Centre Line: A line style used to indicate the axis of symmetry or the centre of a circular feature like a hole or cylinder. Often represented by alternating long and short dashes.
- Bolt Circle: A specific application of a centre line to show the centres of a pattern of holes arranged in a circle.
- Dimensioning: The process of adding measurements and other notes to a drawing to define the size and location of features.
- Layout: The arrangement of views and information on a drawing sheet.
Additional Information: Applications of Bolt Circles
Bolt circles are commonly used in:
- Flanges (for pipes or other connections)
- Wheel hubs (for attaching wheels)
- Gear patterns or sprockets
- Any component requiring multiple fasteners arranged in a circular pattern
The size of the bolt circle is often specified by its diameter, the Bolt Circle Diameter (B.C.D.), and the number of holes on that circle. The angle between adjacent holes can be calculated by dividing 360 degrees by the number of holes.
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