To explain your choice of drawing, name the job the drawing must do, name who will use it, and say what the chosen type shows well and what it shows less well. One clear sentence for each is enough.
This lesson is part of SPM subjects and learning resources. It goes well with reading spatial information from views, because you must understand what each drawing type shows before you can argue for it.
Why do different drawings exist for the same part?
Each type answers a different question. Orthographic views give exact sizes and true shapes. A pictorial drawing gives a quick impression of the whole solid, and a sectional view shows what is inside.
Every type has a trade-off. Orthographic views are precise but make the reader combine three pictures. A pictorial view is easy to read but distorts some lengths and angles.
A three-part frame
Use this frame for any “explain your choice” question.
- Purpose: what must the drawing do?
- Reader: who will use it and what do they need?
- Trade-off: what does this choice show well, and what does it show less well?
The frame fits into two or three sentences, so you can write it quickly in an exam.
Worked example: one part, two situations
The part is a small original shelf bracket, made from flat metal with two screw holes and a bent lip.
Situation A: a workshop will cut and drill the bracket. The best choice is orthographic views with dimensions. The workshop needs true lengths, hole positions and the bend location, and orthographic views show each of these without distortion. The trade-off is that the worker must combine the views mentally to picture the bent part.
Situation B: a shop wants a picture for a customer who is choosing a shelf. The best choice is a pictorial drawing such as isometric. The customer needs to see the shape at a glance, and a single view shows the lip and the holes together. The trade-off is that some lengths are not shown at true size, so it is unsuitable for manufacturing.
The part stayed the same. Only the purpose and the reader changed, and that change is the reason for the different choice.
The mistake that costs marks
A weak answer is: “I chose isometric because it looks better.” It gives a preference, not a purpose, and it would fit any part in any situation.
| Weak | Strong |
|---|---|
| “It looks better.” | “The customer needs to see the whole shape at a glance.” |
| “It is easier.” | “It shows the lip and holes in one view, but not every length at true size.” |
| “It is more detailed.” | “The workshop needs exact hole positions, which views with dimensions give.” |
To test a reason, cover the part name. If the sentence would still fit any other part, make it more specific.
Check yourself
An original part is a wooden stool with a round seat and three legs. Explain why an orthographic set with dimensions suits the carpenter, and why a pictorial drawing suits a catalogue, using the three-part frame for each.
Answer
Carpenter: the purpose is cutting and joining wood to size. The reader is the carpenter, who needs seat diameter, leg length and leg angle at true size. Orthographic views with dimensions show these directly. The trade-off is that the carpenter must join three views to picture the stool.
Catalogue: the purpose is helping a buyer see the finished stool. The reader is a customer who does not read dimensions. A pictorial view shows the round seat and three legs in a single image. The trade-off is that the leg angles are not shown at true size, so it cannot replace the working drawing.
If your answer only said one is “clearer”, add the reader and the trade-off.
What to study next
Next, learn to check consistency between views, so the drawing you justify is also correct. The original practice set mixes reading, choosing and checking questions.
If you want a teacher to question your reasons live and help you sharpen them, see online one-to-one Technical Communication Graphics tuition.