Sectioning and dimensioning a ribbed cast bracket
A cast bracket is 120 mm long, 70 mm wide and 40 mm high, with a vertical web 12 mm thick, two Ø14 mm through holes on a 90 mm pitch, a central Ø30 mm bore with a keyway 8 mm wide, and a triangular rib 10 mm thick joining the web to the base. The part is symmetrical about the longitudinal vertical plane. The proposed drawing sheet uses a full section A–A along the longitudinal plane, hatches the rib, dimensions the Ø14 holes in both the plan and the section, gives the keyway width as 8 without a tolerance, and places the section arrows pointing away from the viewing direction. The checker must decide whether a half section would communicate the bore and keyway better, whether the rib should be hatched, and which dimensions are redundant. The drawing must follow UNE-EN ISO 128 and ISO 129; the workshop reads only the views on the sheet, so missing or duplicated information is costly.
1. Should the triangular rib be hatched in section A–A? Evaluate the full section against a half section for this symmetrical bracket.
Read the worked answer
The rib should not be hatched in section A–A. The cutting plane runs lengthwise through the 10 mm rib, and ISO 128-40 treats ribs, webs and similar thin features cut longitudinally as not sectioned: they are left unhatched, outlined with continuous thick lines, and separated from the adjacent hatched material by a continuous line. Hatching the rib would falsely suggest a solid mass across the cut and would obscure the web-to-base junction.
For the symmetrical bracket, a half section is often more informative: one half shows the exterior and the other half shows the bore, web and base in section, reducing the number of views. However, the keyway is a local feature. If it lies on the unsectioned half, a half section may show it only as a hidden line or omit it. The better judgement is a half section for the overall form plus a local or aligned section through the keyway, or a full section if the keyway lies in the cutting plane. In either case the rib remains unhatched. A transverse cut through the rib would be hatched, but that is not the proposed cut.
2. Identify at least four errors or weaknesses in the proposed dimensioning and section indications, and state the correction for each.
Read the worked answer
Duplicate Ø14 dimensions: the two holes are dimensioned in both plan and section. Dimension them once, on the view that shows them most clearly, as “2 × Ø14” with the 90 mm pitch; delete the repeat.
Keyway width “8” without qualification: dimension it on the section that shows its true width, not on a hidden or foreshortened view. If the keyway mates with a key, give the fit or tolerance (for example 8 H9) or invoke the general tolerance standard; a bare 8 is ambiguous for manufacture.
Section arrows point away from the viewing direction: the arrows must point in the direction of sight, and the section view is placed behind the cutting plane. Reverse the arrows and keep the A–A labelling consistent on both the cutting line and the section view.
Rib hatched: remove the hatching as explained above and outline the rib separately.
Missing thickness dimensions: the 12 mm web and 10 mm rib should be dimensioned where their true thickness is visible, not left to scale or to a hidden line. Do not dimension to hidden edges when a section or local view can show the feature.
The general rule is one dimension per feature, placed on the view that shows the feature in true shape, with symbols Ø and R used correctly and no closed dimension chains that duplicate the same information.
3. Specify a corrected cutting-plane arrangement and section-view presentation that would show the bore, keyway and rib without ambiguity.
Read the worked answer
Use the longitudinal vertical plane of symmetry as the cutting plane, passing through the axis of the Ø30 bore and through the keyway. Label it A–A on the plan or front view, with arrows pointing in the direction of sight. If a full section is chosen, place the section view in the standard projection position behind the cutting plane; hatch the web and base, but leave the 10 mm rib unhatched and outline it.
If a half section is preferred because the bracket is symmetrical, use the same cutting plane but draw one half in section and the other half as an exterior view. The dividing line between the two halves is a thin chain centre line, not a continuous thick line. Make sure the keyway falls in the sectioned half; if it does not, add a local section through the keyway or rotate the half-section boundary so that the keyway is shown.
Dimension the bore as Ø30 with its depth or through condition, the keyway width on the section with its tolerance or general-tolerance note, and the two Ø14 holes once as “2 × Ø14” with the 90 mm pitch. State the general tolerance standard and remove all duplicated dimensions.