To compare a flawed section with its correction, walk through six checks and record each difference in words. Naming each difference is how you avoid it next time.
This lesson is part of sections and spatial reasoning. It applies what a section reveals taught you.
What are the six checks?
- Label: do the letters under the section match the cutting plane line?
- Cut face: is only the cut material hatched?
- Voids: are holes and slots left clear?
- Angle and spacing: is the hatching uniform across one part?
- Boundaries: does hatching stop at outlines without crossing them?
- Hidden lines: are dashed lines left out unless asked for?
Worked example: a bracket block
An original solid is 70 mm wide and 30 mm high, with a through slot 20 mm wide, centred, running the full height. A plane A-A cuts across the width through the slot. A student’s section has four faults.
Fault 1. The slot is hatched over, although it is empty. The plane cuts only the two side strips, each (70 − 20) ÷ 2 = 25 mm wide.
Fault 2. The left strip is hatched at 45° but the right strip at 135°. The two strips belong to one part cut by one plane, so the angle must match.
Fault 3. The label below the drawing reads B-B, but the plane line in the top view says A-A.
Fault 4. The slot’s walls are drawn as dashed lines. After cutting, the walls are visible edges at the plane, so they are thick continuous lines.
The corrected section has two hatched strips, 25 mm wide and 30 mm high, in one direction, a clear 20 mm gap with solid sides and the label A-A.
The mistake: marking as right or wrong
The habit is to judge the whole drawing as one piece. A drawing with four faults and two correct features still gets called wrong, with no indication where.
| Check | Flawed | Corrected |
|---|---|---|
| Label | B-B | A-A |
| Slot | Hatched | Clear |
| Hatch angle | Two angles | One angle |
| Slot walls | Dashed | Solid |
| Strip width | 25 mm | 25 mm |
The last row is correct in both. Seeing which rows agree stops you redrawing parts that were right.
Two faults that hide behind each other
Sometimes a fault is invisible until another is fixed. If the slot is hatched over, you cannot judge its wall lines. Fix voids first, then check the walls. That is why the checklist runs in order.
Check yourself
A student’s section of a 40 mm wide, 20 mm high solid, cut by plane C-C through a central hole of diameter 10 mm, shows the hole hatched at 45°, the side strips hatched at 45°, and the label C-C. Which checks fail, and what are the strip widths?
Answer
Check 3 fails: the hole is empty and must be left clear. Labels and angles are correct.
The plane passes through the centre, so each side strip has width (40 − 10) ÷ 2 = 15 mm, and height 20 mm.
What to study next
Apply the six checks to your own drawings in the sections practice set, or return to interpreting a stated cutting plane if the labels still confuse you.
If you want a teacher to compare your drawings with corrected ones, see online one-to-one Engineering Drawing tuition.