Punjab PSEB Matric Mechanical Drawing and Painting flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Representative fraction (RF)

The ratio of a length on the drawing to the corresponding actual length, written as a fraction such as 1:50, meaning one drawing unit represents fifty real units.

Compass lead point shape

Compass leads are sharpened to a chisel or wedge point, not a needle point, so the line stays of even width as the compass rotates around the centre.

Long-dash-dot line

A thin continuous line of long dashes separated by single dots, used for centre lines, axes of symmetry and pitch circles, and extended slightly beyond the outline.

Standard lettering height

Minimum height of lettering on a technical drawing is 2.5 mm; preferred heights are 2.5, 3.5, 5, 7, 10 and 14 mm, with lowercase about 0.7 times the capital height.

Extension line gap

Extension lines begin about 1 mm clear of the object outline and run 2 to 3 mm past the dimension line, so they never touch the object they locate.

Diameter and radius symbols

A dimension preceded by the symbol Ø denotes a diameter and R denotes a radius; SR and SØ denote spherical radius and spherical diameter respectively.

First-angle projection arrangement

In first-angle projection the object lies between observer and plane, so the front view is placed above the top view and the left-side view appears on the right.

Point in first quadrant

A point above the HP and in front of the VP has its front view above the XY line and its top view below XY, with distances from XY equal to height and depth.

True length of an inclined line

True length appears only in a view where the line is parallel to a reference plane; it is found from a right triangle of plan length and elevation difference.

Horizontal and vertical traces

HT is the point where a line or plane meets the HP and VT where it meets the VP; a line parallel to HP has no HT and one parallel to VP has no VT.

Section plane representation

A cutting plane is shown in the view where it appears as an edge, drawn as a thin long-dash-short-dash line with arrows showing the direction of sight and letters at the ends.

Frustum versus truncated solid

A frustum is cut from a solid by a plane parallel to the base; a truncated solid is cut by an inclined plane, so its cut face is not parallel to the base.

Isometric foreshortening factor

In true isometric projection all three axes are foreshortened equally by 0.816; isometric drawing uses full lengths, making it 1.22 times the true projection.

Isometric ellipse axes

A circle of diameter D drawn in isometric has an ellipse with major axis 1.22 D and minor axis 0.71 D, the major axis lying perpendicular to the cylinder axis.

Cavalier versus cabinet oblique

Cavalier oblique draws the receding axis at full scale, usually at 45 degrees; cabinet oblique draws it at half scale to reduce the apparent distortion of depth.

Isometric versus isometric projection

Isometric drawing sets off true lengths along the three axes; isometric projection applies the 0.816 foreshortening factor, so the same object appears smaller on paper.

Parallel-line development

Used for prisms and cylinders: the base perimeter is divided into equal parts and laid along a straight line, with perpendiculars of the solid's height erected at each division.

Cone development sector angle

The development of a right cone is a sector of radius equal to the slant height L, with sector angle 360 degrees multiplied by base radius r divided by L.

Intersection of equal cylinders

When two cylinders of equal diameter intersect at right angles and share axes in the same plane, the curve of intersection appears as two straight lines crossing at the centre.

Triangulation development

A method for oblique and transition pieces: the surface is divided into triangles, each side's true length is found, and the triangles are laid out in sequence.

Pencil-sight proportion check

Holding a pencil at arm's length, one dimension of the object is measured against another on the pencil and the resulting ratio is transferred to the drawing.

Bounding box in sketching

The object is first enclosed in a light rectangular box or simple solid, and its parts are then cut out of that envelope to keep proportion correct.

Ellipse minor axis direction

In perspective, the minor axis of an ellipse representing a circle always points towards the vanishing point of the cylinder's axis, and the ellipse closes as it nears eye level.

Tint and shade

A tint is a colour lightened by adding white; a shade is a colour darkened by adding black; both change value while the hue stays the same.

Complementary colour pairs

Red with green, yellow with violet and blue with orange; side by side they intensify each other, and mixed in pigment they neutralise towards grey or brown.

Fat over lean rule

In oil painting each successive layer contains more oil and less solvent than the one beneath, so the upper layers dry flexibly and do not crack.

Watercolour white

Watercolour is transparent and takes its lights from the white paper; opaque white pigment is not used as a body colour, so light areas are left unpainted.

Rule of thirds

The picture is divided into thirds horizontally and vertically, and the centre of interest is placed near one of the four intersections rather than at the centre.

Aerial perspective

Distant objects appear lighter in value, cooler in colour, lower in contrast and less detailed than foreground objects because of atmosphere between viewer and subject.

Asymmetrical balance

An informal composition balances unequal shapes or numbers by adjusting their visual weight through size, tone, colour intensity or placement relative to the centre.

Still life light source

A single light from one side of the group gives consistent shadows, a clear light-and-dark pattern and a readable form for each object in the arrangement.

Focal point in composition

The area of greatest contrast or detail that first attracts the eye; leading lines, repeated shapes and tone edges direct the viewer towards it.