Check your own drawing against a fixed list. Looking at it again and hoping to spot errors does not work. Five checks cover both the dimensions and the agreement between views.
This lesson is part of SPM subjects and learning resources. It assumes you know the alignment rules from checking consistency between views.
The five-check routine
Run the checks in this order, marking your sheet as you go.
- Totals: do the parts add up to each overall dimension?
- Once only: is each feature dimensioned a single time?
- Coverage: can a reader build the object without measuring the drawing?
- Placement: are dimensions outside the views, clear of the lines, with the overall size outermost?
- Agreement: do width, height and depth match across the views?
Use three marks. A tick means the check passed, a circle means there is a problem, and a question mark means you are unsure and need to find out.
Worked example: a chain that does not add up
This is an original drawing of a flat base plate. The student’s front view shows an overall width of 80. Along the bottom, the dimension chain reads 15, 30 and 40 for a slot, a block and a gap.
Check 1: totals. Add the chain: 15 + 30 + 40 = 85. The overall width says 80. The numbers disagree by 5, so the student circles the chain.
Finding the fault. The top view shows the gap measured from the slot edge to the right edge. Re-measuring on the drawing gives the gap as 35, and 15 + 30 + 35 = 80. The mistake was a misread when copying the size.
Check 2: once only. The student finds that the 30-wide block is dimensioned in both the front and top views. One of the two is removed, so the reader sees the size only once.
Check 3: coverage. The slot has a width in the chain, but its height was never dimensioned. The student adds the height in the side view.
The sheet now passes the first three checks. Checks 4 and 5 are still to do.
The mistake that costs marks
Many students treat the overall dimension as “extra” and skip the addition. The overall size and the chain then disagree without anyone noticing, and the reader cannot tell which one is wrong.
The fix takes about ten seconds. Each time you finish a chain, write the sum in the margin in pencil and compare it with the overall figure before you move on.
Check yourself
A drawing of a rectangular frame has an overall height of 120. The side dimension chain reads 25, 50 and 35.
The top rail is listed as 25, the window opening as 50 and the bottom rail as 35. Does it pass the totals check? What should the student do?
Answer
Add the chain: 25 + 50 + 35 = 110. The overall height is 120, so the chain is short by 10.
The student should not change a number at random. Go back to the brief or the original object and find which part is 10 larger. If the window opening is really 60, the chain becomes 25 + 60 + 35 = 120 and the drawing passes. If the overall height is wrong, the overall figure is changed to 110.
Whichever number is corrected, repeat the agreement check, because the height also appears in the other views.
What to study next
Test yourself across the whole skill set with the original practice questions. You can also use the structured-answer self-review tool to check the written parts of an answer.
If you want a teacher to go through your own drawing with you and show which checks you skip, see online one-to-one Technical Communication Graphics tuition.