Short Answer:

In a freehand sketch, hidden edges are represented using dashed or broken lines. These lines show the parts of the object that are not visible from the current viewing direction but still exist behind or inside the solid object. The dashes are evenly spaced and drawn lightly compared to the visible outlines.

Using hidden lines in freehand sketches is important because it helps to show the complete shape and features of the part, even those that are not seen directly. This gives a clear understanding of holes, slots, or inner walls in mechanical components.

Detailed Explanation:

Representation of Hidden Edges in Freehand Sketch

When engineers or draftsmen create technical drawings or freehand sketches, they aim to show the true shape and structure of a part. But many objects have internal or back-side features that are not visible from the outside. These are called hidden edges, and they must be shown using a special line style so the viewer understands the full shape of the part.

In engineering, correct use of hidden lines is very important to ensure clear communication, especially during manufacturing, inspection, or assembly. Even in freehand sketching, following this rule gives a more accurate and complete sketch.

How Hidden Edges Are Represented

Hidden edges are shown using dashed lines, also called hidden lines.
The dashes are uniform in length, and equally spaced.
They are drawn lighter and thinner than visible outlines so that the main shape remains dominant.

For example:

A hole at the back of a block is shown as a dashed circle.
A slot inside a body is shown with dashed lines to indicate its position.

These lines tell the reader: “This part is not visible from the outside but still exists behind.”

Steps to Draw Hidden Edges in Freehand Sketch

Sketch the visible edges of the object with dark continuous lines.
Visualize or imagine the hidden part inside or behind the object.
Use a light touch to draw the dashed lines in the correct location and size.
Make sure the dashes are uniform and do not connect into solid lines.
Avoid overusing hidden lines to keep the drawing clear and neat.

Note: In some cases, if too many hidden lines make the sketch confusing, it’s better to add a sectional view to show inner features.

Rules and Conventions to Follow

The length of each dash should be around 2 to 3 mm.
The gap between dashes should be around 1 mm.
Avoid starting or ending a hidden line with a gap—start and end with a dash when possible.
In corners, do not connect hidden lines to solid lines directly.
Hidden lines should not overlap dimension lines.

Following these rules ensures your freehand sketch is clear, professional, and easy to understand.

Importance of Showing Hidden Edges

Helps in showing the complete geometry of a part.
Essential for parts with holes, internal slots, or recesses.
Avoids misunderstanding or error in fabrication.
Makes the sketch look technically correct and complete.
Builds good habits for detailed drafting and CAD work.

Even though freehand sketches are rough, they should still follow standard practices to communicate correctly.

Common Examples Where Hidden Edges Are Used

A drilled hole that doesn’t go all the way through.
A rectangular slot on the back face of a cube.
Internal ribs or supports in casting.
Grooves or channels hidden from view.

By using dashed lines, you make these hidden features visible to the reader without opening or cutting the object.

Conclusion

In a freehand sketch, hidden edges are represented using dashed lines to show features that are not directly visible. This method helps the viewer understand the complete structure of the object, including internal and back-side elements. Proper use of hidden lines improves the clarity, professionalism, and technical correctness of the drawing. Every engineer and student should practice this to make their sketches more meaningful and complete.