Skills practice questions.

A full section is taken through an assembly along the length of a solid shaft and of the bolt that retains it, so that the cutting plane runs down the axis of both. How are the shaft and the bolt shown in that sectional view?

• Hatched in the same direction as the housing around them
• Left unhatched and drawn as outside views
• Hatched at 30 degrees so that they read as fixings
• Omitted from the section and shown on the plan only

Answer: Left unhatched and drawn as outside views

Shafts, bolts, nuts, pins, keys, ribs and webs are conventionally not sectioned when the cutting plane runs along their length, because hatching them adds nothing and hides their form. They are hatched only where the plane cuts across their axis.

On an engineering drawing a chain line of alternating long and short dashes runs through the middle of a drilled hole. The line is thin over its whole length, is not thickened at its ends and carries neither viewing arrows nor reference letters, and it stops a short distance beyond the outline. What does this line represent?

• An edge that is hidden behind the visible surface
• The visible outline of the machined bore
• The centre line or axis of the hole
• The boundary of the area covered by a surface finish note

Answer: The centre line or axis of the hole

A chain line that stays thin from end to end marks an axis or a line of symmetry and is extended slightly beyond the feature it locates. The cutting plane of a section uses the same dash pattern but is thickened at its ends and at every change of direction and carries viewing arrows and reference letters.

A detail drawing of a small bracket carries the note SCALE 2:1. A hole on the drawing measures 24 mm across. What is the true diameter of the hole on the finished part?

• 12 mm; the drawing is twice full size
• 24 mm; the drawing is full size
• 48 mm; the drawing is half full size
• 6 mm; the drawing is four times full size

Answer: 12 mm; the drawing is twice full size

In the notation drawn size to true size, 2:1 means the drawing is twice as large as the part, so 24 mm on paper is 12 mm of metal. The reduction 1:2 is the case that doubles the drawn dimension.

In a sectional assembly drawing, two touching components are hatched with lines sloping in opposite directions. What does this convention communicate?

• They are made from the same material
• The view is a half section rather than a full section
• Those surfaces are machined after casting
• They are two separate components meeting at a joint

Answer: They are two separate components meeting at a joint

Hatching direction, angle and spacing are varied only so that the reader can see where one part ends and the next begins on the cut plane. A single component is hatched identically wherever it is cut in the drawing.

A hole on a detail drawing is dimensioned 12 +/- 0.05 mm. What does the figure 0.05 state?

• The surface roughness of the bore in micrometres
• The clearance between the hole and its mating shaft
• The scale to which the hole has been drawn
• The permitted variation on the size of the hole

Answer: The permitted variation on the size of the hole

The figure is the tolerance, so any hole between 11.95 mm and 12.05 mm is acceptable. It describes the manufacturing limits of this feature alone and says nothing about surface finish or about the fit with a shaft, which depends on the shaft tolerance as well.

At what angle to the horizontal are the two receding base edges of a rectangular block constructed in an isometric drawing?

• 30 degrees on both sides of the vertical front edge
• 45 degrees on both sides of the vertical front edge
• 30 degrees on one side and 60 degrees on the other
• 60 degrees on both sides of the vertical front edge

Answer: 30 degrees on both sides of the vertical front edge

An isometric drawing uses two axes at 30 degrees to the horizontal plus one vertical axis, and all three are measured at the same scale, which is what makes lengths readable from the drawing. Converging receding edges belong to perspective instead.