Basic Blueprint Reading

Drawings are the common language of the workplace

If you say "please cut this part by 5mm," people will understand it differently. Drawings are an agreement made so that everyone who reads it produces the same object.

Third Angle Projection — the standard in Korea, Japan, and the U.S.

This is a method of arranging a 3D object viewed from multiple directions onto a flat surface. Place the view where it is seen.

              ┌─────────┐
              │ Top View │   ← View from above
              └─────────┘
   ┌─────────┐┌─────────┐┌─────────┐
   │Left View ││ Front View ││Right View │
   └─────────┘└─────────┘└─────────┘
              ┌─────────┐
              │ Bottom View │
              └─────────┘

What is seen from above is placed above, and what is seen from the right is placed on the right. It's intuitive.

It is different from First Angle Projection

Europe and China use First Angle Projection, and the arrangement is completely opposite (what is seen from the right is placed on the left). If you misread the drawing, you will end up with a part that is mirrored left and right.

That is why the projection symbol must always be present in the drawing title block.

Third Angle Symbol        First Angle Symbol
  ⊂|⊃                ⊂|⊃
 (The narrow side of the cone faces the circle)       (The wide side of the cone faces the circle)

> When you receive drawings from overseas, check the projection method first. Especially drawings from Chinese and European suppliers often use First Angle Projection.

Line types convey information

The more hidden lines there are, the more complex the drawing becomes. That is why cross-sectional views are used.

Cross-sectional View

It shows the inside of an object by cutting it. The cut surface is marked with hatching (cross-hatching).

> Do not cut axles, bolts, ribs, keys, or pins vertically. There is nothing to see inside, and it can cause confusion.

Auxiliary View

When viewed with an orthogonal projection, inclined surfaces appear distorted. To see the actual shape, an auxiliary view that is viewed perpendicular to that surface is needed.

Scale

1:1   Full size (actual size)
1:2   Reduced scale (drawn at 1/2 of actual size)
2:1   Enlarged scale (drawn at 2 times actual size)

Important: Do not measure the size drawn on the drawing with a ruler and use that. Always follow the dimension numbers that are explicitly written. There are cases where the scale and actual dimensions differ (NS, Not to Scale).

Title Block — the first place to check

It is located at the bottom right of the drawing.

> Checking the revision number is really important. It is common for old drawings to be floating around the site, and using them for processing can lead to total rejection. Proper drawing management (only the latest version on site) is the basis of quality.

New Employee Practical Steps

1. Title Block — Part name, drawing number, Rev, material, scale, projection method
2. Understand the overall shape — Start with the front view
3. Main dimensions — Overall length, width, height
4. Machining areas — Holes, threads, slots
5. Identify tight tolerance areas — These are important dimensions
6. Read the notes (NOTE) — Instructions such as heat treatment, plating, burr removal

> It is common to make mistakes by not reading the notes (NOTE), such as forgetting heat treatment. Even text in a corner of the drawing is part of the drawing.