How do you determine the correct scale for an orthographic drawing?

Short Answer:

The correct scale for an orthographic drawing is determined by considering the actual size of the object and the available drawing sheet size. The goal is to make sure the drawing fits neatly on the sheet while still being large enough to show all important details clearly.

Scales can be full scale (1:1), reduced (like 1:2 or 1:10), or enlarged (like 2:1 or 5:1) depending on the object. By analyzing the overall dimensions, detail requirements, and drawing sheet size, we can select the most suitable scale for clear and accurate representation.

Detailed Explanation:

How to Determine the Correct Scale for an Orthographic Drawing

In engineering drawing, a scale is the ratio between the size of the object in real life and the size shown in the drawing. Since mechanical components can be very large or very small, it’s not always practical to draw them at full size. So, we use a scale to reduce or enlarge the size while still maintaining accuracy and proportions.

Orthographic drawings include multiple 2D views (front, top, side, etc.), and all of them must be drawn to the same scale so that they can be understood together. Choosing the correct scale is very important for a clear, readable, and professional-looking drawing.

Steps to Determine the Correct Scale

  1. Check the Actual Size of the Object
  • Start by finding out the overall dimensions of the object (length, width, height).
  • This helps in estimating how much space the drawing will take on paper if drawn full size (1:1).
  1. Choose the Drawing Sheet Size
  • Standard sheet sizes include A0, A1, A2, A3, and A4.
  • The choice of sheet depends on the type of drawing, complexity, and company standards.
  • Make sure to leave room for title block, dimensions, notes, and views.
  1. Compare Object Size to Sheet Size
  • Now check whether the full-size drawing fits on the selected sheet.
  • If the object is too large, choose a reduced scale (e.g., 1:2, 1:5, 1:10).
  • If the object is very small, use an enlarged scale (e.g., 2:1, 5:1).

Example:
If a component is 1000 mm long and your sheet width is only 420 mm (A3), then drawing it at full scale won’t fit. A scale of 1:2 or 1:5 would be better.

  1. Consider Level of Detail Needed
  • If your part has fine features or small holes, the scale should be large enough to show them clearly.
  • Don’t choose a scale that makes details too small to see or dimension.
  1. Follow Standards or Company Guidelines
  • Use BIS, ISO, or company standards for recommended scales.
  • For mechanical drawings, common scales include:
    • Full scale (1:1)
    • Reducing scales: 1:2, 1:5, 1:10, 1:20, 1:50
    • Enlarging scales: 2:1, 5:1, 10:1
  1. Keep All Views to Same Scale
  • In orthographic projection, all views (front, top, side) must be to the same scale for correctness.
  • If additional detail views are needed, they can use a different scale, but this should be clearly mentioned.
  1. Mention the Scale Clearly in the Title Block
  • Always write the scale used in the title block of the drawing.
  • If more than one scale is used (e.g., a detail view), label each view properly (e.g., “DETAIL A SCALE 2:1”).

Tips for Choosing the Right Scale

  • Prefer to use full scale (1:1) when possible.
  • If reduced, choose the largest scale that fits the drawing.
  • Avoid making parts too small or too large—the goal is clarity and fit.
  • Use enlarged scale for showing tiny features like threads or micro-components.
Conclusion

Determining the correct scale for an orthographic drawing depends on the real size of the object, the available sheet size, and the clarity needed for the viewer. By checking dimensions, sheet space, and detail level, the right scale can be selected to ensure the drawing is accurate, clear, and professional. Using the proper scale also helps in communication, manufacturing, and inspection by providing the right level of visual information without crowding the sheet.