To infer a missing view, first describe the object in words, using width, height and depth from the two views you have. Then project that description into the third view.
This lesson is in orthographic views and follows relating front, top and side views.
What is the routine?
Use four steps every time.
- Read the two given views and list width, height and depth.
- Describe the object in one sentence.
- Imagine standing where the missing view is taken, and sketch only what you would see.
- Add dashed lines for any edge covered by a nearer part.
Worked example: an L-shaped block
The given views are in first angle projection.
The front view is an L-shape: a tall part on the left, 30 mm wide and 40 mm high, and a lower part on the right, 30 mm wide and 20 mm high. The total width is 60 mm. The top view is a rectangle 60 mm wide and 30 mm deep, with a vertical line at x = 30.
The missing view is the view from the left.
Step 1. Width 60, height 40, depth 30.
Step 2. The object is a block 30 mm deep, with a full-height column on the left (30 × 40) and a lower step on the right (30 × 20). Both parts are the full depth of 30 mm, since the top view shows one rectangle 30 deep.
Step 3. From the left, the tall column hides the lower step. The outline is a rectangle 30 mm wide (depth) and 40 mm high.
Step 4. The top of the lower step is at height 20 mm. It is behind the tall column, so it is drawn as a dashed line across the rectangle at height 20.
The finished side view is a 30 × 40 rectangle with one dashed line at height 20 mm.
The mistake: drawing only the silhouette
A quick sketch stops at step 3, leaving a plain rectangle. The outline is right, but the view is incomplete because it says the object has no edge at height 20.
| Step | Wrong | Right |
|---|---|---|
| Outline | 30 × 40 rectangle | 30 × 40 rectangle |
| Dashed line at 20 | Missing | Present |
| What it implies | A solid column all the way | A column with a lower step behind |
A view that omits hidden edges describes a simpler object than the one given.
A second example: swapping the side
Keep the same block but ask for the view from the right. The lower step is now nearest the viewer and the tall column is behind it.
The outline is still 30 × 40, but the line at height 20 is now a solid line, because the step’s top edge is fully visible. The only change is the line type, so the direction of viewing decides what is hidden.
Check yourself
The front view is a rectangle 40 wide and 25 high, with two dashed vertical lines 10 mm apart, centred, running from the top edge to the bottom edge. The top view is a rectangle 40 wide and 20 deep with a circle of diameter 10 at its centre. Describe the object and draw the side view.
Answer
The object is a block 40 × 20 × 25 mm with a round hole of diameter 10 mm, centred, going through the full height. The dashed lines in the front view sit 15 mm and 25 mm from the left edge, because (40 − 10) ÷ 2 = 15.
The side view outline is a rectangle 20 wide and 25 high. The hole is hidden from the side, so it appears as two dashed vertical lines 10 mm apart, 5 mm in from each side edge, running the full height.
What to study next
Practise hidden-line decisions in distinguishing visible and hidden features, then use the practice set.
If you want a teacher to give you pairs of views and mark your third view, see online one-to-one Engineering Drawing tuition.