Assam ASSEB HS Skill Engineering Drawing flashcards

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

A0 sheet size

A0 measures 1189 mm by 841 mm with an area of one square metre. Each lower size in the ISO A series halves the longer side, giving A1 841 × 594 mm and A2 594 × 420 mm.

Line precedence rule

Where lines coincide, draw the visible outline first, then hidden line, then centre line, then dimension and extension lines, and lastly the cutting-plane line. This keeps the most informative line visible.

Pencil grade selection

Use 2H or H for construction and projection lines, HB for lettering and freehand sketching, and 2B or softer for final visible outlines where a dark, heavy line is wanted.

Title block location

The title block is placed at the bottom-right corner of every sheet and records drawing number, title, scale, sheet size, projection symbol, date, and approval signatures.

Aligned versus unidirectional dimensioning

In the aligned system numerals are written parallel to the dimension line and read from the bottom or right edge. In the unidirectional system all numerals stay horizontal regardless of line direction.

Dimensioning hidden lines

Dimensions are not placed on hidden lines because the value cannot be read clearly and the line is broken by dashes. Locate the feature with a section view or a visible edge instead.

Ellipse construction methods

The concentric-circle method projects points from circles drawn on the major and minor axes. The foci method uses the constant sum of distances from the two foci to any point on the curve.

Regular polygon construction

Divide the vertical diameter of the circumscribing circle into n equal parts, then draw lines from the top vertex through the division points; where they cut the circle are the polygon vertices.

First-angle projection layout

The object lies between the observer and the plane. The top view is therefore placed below the front view, and the view seen from the left is placed on the right of the front view.

True length of an inclined line

A line shows true length in the view where it is parallel to the reference plane. A line parallel to HP and inclined to VP shows true length and true inclination in the front view.

Apparent versus true angle

The angle a line makes with a plane in projection is only apparent unless the line's other view is parallel to XY. Apparent angles are always larger than the true inclination.

Horizontal and vertical traces

HT is the point where a line or plane meets the horizontal plane, and VT is where it meets the vertical plane. A line parallel to a plane has no trace on that plane.

Simple position of a solid

A solid is first drawn with its axis perpendicular to one reference plane, resting on HP or parallel to VP. Tilting to the required angle is done in a second stage.

Cone section shapes

A plane parallel to the base gives a circle, a plane inclined less than the slant gives an ellipse, a plane parallel to a generator gives a parabola, and a steeper plane gives a hyperbola.

True shape of a section

Project the section points onto an auxiliary plane parallel to the cutting plane, then measure distances perpendicular to the cutting-plane line to obtain the true shape.

Section hatching convention

The cut surface is hatched with thin continuous lines at 45° to the main outline, evenly spaced. Adjacent parts in an assembly are hatched in opposite directions.

Cylinder lateral development

The lateral surface of a right cylinder unfolds into a rectangle whose width equals π times the diameter and whose height equals the cylinder height.

Cone development sector

The lateral surface of a right cone develops into a sector of radius equal to the slant height L, with sector angle 360° × R / L, where R is the base radius.

Triangulation development

Used 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 to form the development.

Equal cylinder intersection

Two cylinders of equal diameter whose axes intersect give two straight lines as the line of intersection in the front view, because the surfaces meet along plane curves that project as lines.

Isometric axes and angles

The three isometric axes are 120° apart and are drawn at 30° to the horizontal. All three are equally foreshortened by about 0.816 in true isometric projection.

Isometric ellipse axes

A circle of diameter D on an isometric face becomes an ellipse with major axis about 1.22 D and minor axis about 0.71 D. The major axis is perpendicular to the axis normal to that face.

Cavalier versus cabinet oblique

Both draw the front face true shape. Cavalier uses full scale on the receding axis and looks deep; cabinet uses half scale, which reduces distortion and is preferred for most drawings.

Non-isometric line

A line not parallel to any of the three isometric axes. Its true length cannot be scaled along the axes, so its endpoints must be located by coordinates and then joined.

Metric thread designation

M20 × 2.5 denotes a metric thread of 20 mm nominal diameter and 2.5 mm pitch. The minor (root) diameter is roughly d minus 1.2268 times the pitch.

Sunk key function

A sunk key sits half in the shaft keyway and half in the hub keyway, transmitting torque by shear and bearing. A saddle key relies on friction and suits light loads only.

Flange coupling parts

Two flanges keyed to the shaft ends are bolted together, so torque passes through the keys and bolts. A protective circumferential projection on one flange acts as a safety guard.

Ball bearing bore number

The last two digits of a bearing designation give the bore in units of 5 mm, so a 6205 bearing has a 25 mm bore. The preceding digits indicate the series and type.

Floor plan wall convention

Walls appear as two parallel lines at the wall thickness, with door openings shown by a leaf and swing arc, and windows shown by lines drawn across the wall thickness.

Building drawing scales

Site plans use 1:500 or 1:1000, floor plans 1:100, and enlarged details 1:20 or 1:10. Every drawing states its scale in the title block.

Staircase proportion rule

The relation 2 × riser + tread ≈ 600 mm gives comfortable stair proportions, with risers typically 150–190 mm. Minimum headroom above the stair is about 2.1 m.

CAD relative polar entry

Typing @distance<angle specifies a point at that distance and angle from the previous point. The @ prefix makes the coordinate relative rather than absolute.