The Drawing That Does Not Close
You are given a revision-B drawing of a mounting bracket to make 40 pieces. The overall length is dimensioned 240 mm, and the same hole is located 150 mm from the left edge and 100 mm from the right edge. A 6 mm fillet weld symbol appears on the arrow side where the bracket meets the base plate, but the general note reads: ALL FILLET WELDS 4 mm UNLESS OTHERWISE STATED. The projection symbol in the title block is first-angle, yet the view placed to the right of the front view is labelled VIEW FROM THE RIGHT. A second print marked Rev A lies on the bench and differs in hole position by 5 mm. Scaling the Rev B print with a steel rule gives 145 mm for the 150 mm dimension. The foreman says to cut all 40 pieces because the drawing is roughly right, and the customer's inspector is due in three days.
1. List each conflict on the drawing and state the rule you would apply to it.
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| Conflict | Rule to apply | What it means here |
|---|---|---|
| 150 + 100 = 250 mm against a 240 mm overall | A part must never be over-dimensioned; a dimension is usable only when the chain closes | One of the three is wrong. Do not average, split the difference or divide 10 mm by two - query it |
| Specific 6 mm weld symbol against the general note of 4 mm | The instruction on the feature overrides the general note | Weld 6 mm leg at that joint, 4 mm everywhere else |
| First-angle symbol, but the view placed on the right is labelled VIEW FROM THE RIGHT | In first angle the view from the right is placed on the left of the front view. The symbol is the declared convention | The view arrangement or the label is wrong. If the bracket is symmetric about that axis the error may be harmless - check symmetry before panicking |
| Rev A on the bench, Rev B at the machine | The latest approved revision governs, and superseded prints must be withdrawn from the workplace | Work to Rev B only |
| Scaled 145 mm against dimensioned 150 mm | Dimensions govern; never scale a drawing | Use 150 mm |
2. What must you do before any of the 40 pieces are cut?
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Do not cut the batch. The steps are:
- Raise a drawing query in writing through the foreman to the customer's designer, listing every point with your reading of it and a proposed resolution, for example: confirm 150 mm from the left edge and treat 100 mm as reference; confirm the 6 mm fillet; confirm first-angle.
- Withdraw Rev A from the bench, stamp or write SUPERSEDED on it, and keep only Rev B at the machine with the revision letter visible at every station.
- Make one first-off piece from scrap and trial-fit it to the mating base plate or the assembly drawing. The hole position is almost certainly functional against the mating part, and the assembly drawing shows which dimension matters.
- Get the answer back in writing - an email or a signed note on the print - before releasing the batch, and record the clarification number on the job card.
- Protect the schedule honestly: the 240 overall length is common to both readings of the hole, so blanks can still be cut and marked with the holes left undrilled while the query is open. Warn that the inspector's visit may slip by a day; 40 rejected brackets cost far more than a one-day slip.
3. For the over-dimensioned hole, what is likely intended and how would you settle it without guessing?
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The three dimensions form a closed chain with 10 mm of inconsistency, so at least one is wrong. The likely readings are:
- 240 overall with the hole 150 from the left, and the 100 is a stale dimension left over from Rev A. This is plausible because Rev A differs by 5 mm in hole position, not 10, so the 100 is probably not simply Rev A's value either, but a dimension to a different feature.
- 100 measured from the edge of the base plate rather than from the end of the bracket - common when two parts are dimensioned from different datums.
- 240 is a typing error for 250, which is less likely, since the overall length usually appears elsewhere in the assembly.
How to settle it: check the assembly drawing and the mating part; measure an old bracket if one is available; and look for which dimension carries a tolerance or a fit callout - the functional dimension usually does, while the reference dimension often has none. Then have the designer confirm one dimension as reference and ask for the duplicate to be deleted at the next revision so the error cannot recur. If a decision must be taken on the floor, take the reading supported by the functional dimension and get it signed.