The Overall Length That Reads 170 on a 180 mm Lever
A 180 mm long, 30 mm wide lever is detailed on an A3 sheet at 1:2. One end carries an R10 corner fillet; the other end has a 2 × 45° chamfer around the end face. The drawing's overall-length dimension reads 170.00. The inspector rejects the first article because his calipers read 180 on the finished part. He also measures the chamfer in the 2:1 detail view as 4 mm on the printed sheet and writes it up as a second nonconformance. The drafter maintains that the model is correct and that the drawing was produced 'straight from the model with smart dimensions and it rebuilt clean'.
1. Where does 170.00 come from, and what does the drafter need to select instead?
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Check the delta first: 180 − 170 = 10 mm, exactly the R10 fillet radius. That is the diagnosis. The dimension was attached to the tangent (silhouette) edge where the fillet arc meets the flat end face, not to the end face itself. The tangent edge sits a full radius inboard of the true end of the part.
Why it happened: in a shaded or hidden-line-removed view, tangent edges are selectable and look like real edges, especially at a corner. Smart dimension will happily attach to whichever edge the cursor lands on. The model is indeed correct; the annotation is attached to the wrong topology.
Fix: attach the dimension to the end face edge (the true extremity), or use Find Intersection / a sketch point on the theoretical sharp corner, or hide tangent edges (Display Style → Tangent Edges Removed / With Font) so the wrong edge cannot be picked. Then rebuild and confirm 180.00.
General check: any dimension whose error equals a known fillet or chamfer size is a tangent-edge or chamfered-edge attach error, not a modelling error. Look for that signature rather than re-modelling the part.
2. The inspector measured the 2 mm chamfer as 4 mm on the printed detail view. Explain what is going on and what the correct response to the nonconformance is.
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Sheet and view scale change the size on paper, never the dimension text.
- The detail view is placed at 2:1. A 2 mm chamfer is drawn 4 mm long on the sheet. The inspector's ruler is measuring the drawing, not the part.
- The main view is at 1:2, so a 180 mm part is drawn 90 mm long.
- A correctly created drawing dimension always reports the model value, regardless of view scale or sheet scale. So a chamfer dimension on that detail should read 2.00, even though it measures 4 mm on the paper.
Correct response: reject the nonconformance as a measurement error, and state the rule explicitly - a drawing is not to scale and shall not be scaled; only the dimension text is authoritative. Then check the part itself with a caliper at the chamfer or by optical comparison against the 2.00 dimension.
Worth checking while you are there: confirm the detail view's scale is set in the view properties (not just the annotation note), because a hand-typed '2:1' label over a view that is actually 1:1 is a real defect, and it would produce exactly this confusion with no excuse.
3. What would you add to the drawing standards for this team so the same two problems do not recur?
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Both defects came from annotation practice, not modelling, so the fix belongs in the drawing standard:
Edge and tangent control
- Set Tangent Edges → Removed or With Font in the document template, so silhouette edges of fillets and rounds cannot be picked accidentally.
- Dimension overall sizes to true extremities or theoretical intersections; never to a tangent edge.
- Teach the tell: if a dimension is off by a value that matches a known radius or chamfer, look at edge attachment before touching the model.
Scale discipline
- Sheet scale and view scale set in properties, never typed into a note by hand.
- A note on the template: Do not scale drawing.
- Detail views must carry their scale from the view properties so the label and the geometry cannot disagree.
Release check
- Dimension the overall envelope first and confirm it against the model's bounding box; any mismatch stops the release.
- Have one person other than the drafter check the extremes - the person who attached the tangent dimension will not see it again.