Auxiliary Views

≈ 36 min

Auxiliary Views

A face that is inclined to all three principal planes appears foreshortened in every standard view — front, top and side all show it shorter than it really is. To show its true shape you need an auxiliary view: a view taken looking squarely at that inclined face.

The method: set up a new projection plane parallel to the inclined face, project each corner of the face at 90° onto it, then transfer the depth measurements from an existing view.

Worked example. A block with a 30° sloping face carrying two holes. In the front view the sloping face is a line; in the top view the holes appear as ellipses at the wrong spacing. Only the auxiliary view, taken perpendicular to the slope, shows the face at true size with the holes correctly round and correctly spaced — which is what a machinist needs to drill them.

Core checkpoint: Project perpendicular to the inclined surface. Any other direction gives another foreshortened view, not a true shape.

Why is an auxiliary view needed for a face inclined to all three principal planes?

Because the face is foreshortened in every standard view, so none of them shows its true shape.

Because the face cannot be dimensioned at all otherwise.

Because standard views cannot show holes.

Because it makes the drawing look more complete.

In which direction must the auxiliary view be projected?

Perpendicular to the inclined face.

Parallel to the front view.

At 45° to the horizontal.

In any convenient direction with space on the sheet.

A learner dimensions the sloping face using its length as it appears in the front view. What happens to the manufactured part?

The sloping face comes out shorter than intended, because the front view shows it foreshortened.

The part is correct — the front view shows true length.

The part comes out too long.

Only the surface finish is affected.

How do circular holes on an inclined face appear in the standard top view, and why does that matter?

As ellipses at incorrect apparent spacing, so they cannot be used to set out the drilling positions.

As perfect circles at correct spacing, so the top view is sufficient.

They do not appear at all in the top view.

As squares, because of the projection angle.