JCE Technical Drawing flashcards

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

Perpendicular bisector construction

Draw equal-radius arcs from both endpoints of a line with radius greater than half the length; the line through the two arc intersections is perpendicular to the original line and bisects it.

Dividing a line into n parts

Draw an auxiliary line at any angle from one endpoint, step off n equal divisions, connect the last division to the other endpoint, and draw parallel lines through each division point.

Ellipse by concentric circles

Draw major and minor circles sharing a center; draw radial lines; from each radial intersection with the major circle drop a vertical, from the minor circle draw a horizontal; intersections lie on the ellipse.

First-angle projection arrangement

The object lies between observer and plane; the view from above (plan) is placed below the front view, and the left-side view is placed on the right of the front view.

Third-angle projection arrangement

The plane lies between observer and object; the top view is placed above the front view, and the right-side view is placed on the right of the front view.

Alignment of orthographic views

Front and top views share width and align vertically; front and side views share height and align horizontally; top and side views share depth, transferred by a 45° mitre line.

Hidden line convention

Hidden edges are drawn as short dashes of uniform length and spacing, thinner than visible outlines; they are omitted when they would clutter the view or when a section clarifies the feature.

Isometric axes

Three axes spaced 120° apart, drawn with the vertical axis vertical and the other two at 30° above the horizontal; true lengths are measured along each axis in an isometric drawing.

Non-isometric line

A line in an isometric view that is not parallel to any isometric axis; its endpoints are located on isometric lines and connected, and its true length cannot be scaled directly.

Cabinet oblique projection

An oblique pictorial with the front face true shape and the receding axis at 45° drawn at half scale to reduce the distortion of depth.

Four-center isometric ellipse

An approximation of an isometric circle using four arcs: centers at the corners of the isometric square for the large arcs and at the midpoints of the sides for the small arcs.

Freehand line technique

Keep the eye on the endpoint, move the whole arm from the shoulder, and rotate the paper for long strokes; construction lines are light and final outlines are darkened.

Missing-view reconstruction

Project known features from two views to the third; each point must appear at the same height in front and side views and the same depth in top and side views.

Proportion in sketching

Establish a unit length from a known dimension, compare all other dimensions to that unit by eye or with the pencil at arm's length, and block in the bounding box before detailing.

Extension line gap

A small gap of about 1.5 mm is left between the object outline and the start of the extension line; the extension line extends about 3 mm beyond the dimension line.

Diameter and radius symbols

A diameter is indicated by the symbol Ø placed before the number; a radius by R; a spherical radius by SR; a spherical diameter by SØ.

Representative fraction (RF)

The ratio of drawing length to actual length, written as a fraction; for scale 1:50 the RF is 1/50, meaning one drawing unit represents 50 actual units.

Diagonal scale

A scale that provides three levels of subdivision: main units along the base, tenths along the first division, and hundredths by diagonal lines across a small rectangle.

Cutting plane line

A thick chain line with arrows at the ends showing the direction of sight, labeled with letters such as A-A, used to indicate where a sectional view is taken.

Hatching convention

Thin continuous lines at 45° to the horizontal, equally spaced, used to indicate cut material; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

Ribs not hatched

Ribs, webs, and similar thin features are not section-lined when cut longitudinally; they are shown in outside view to avoid a false impression of solidity.

Half section

A sectional view in which one quarter of the object is removed, showing half the view in section and half in outside view; used for symmetrical objects.

Parallel-line development

A development method for prisms and cylinders in which parallel lines represent the surface elements; the true width equals the circumference or perimeter.

Cone development sector angle

For a right cone, the development is a sector of radius equal to the slant height; the sector angle equals 360° multiplied by the base radius divided by the slant height.

Triangulation development

A development method for oblique or non-developable surfaces in which the surface is divided into triangles, true lengths of sides are found, and triangles are laid out in sequence.

Development of truncated cylinder

Divide the base circle into equal parts, project each element height to a rectangle of width equal to the circumference, and plot the curved edge through the projected points.

Pencil grades for drafting

H or 2H for construction and guidelines; HB or B for visible outlines and lettering; harder leads give lighter, sharper lines and softer leads give darker, broader lines.

Alphabet of lines

Standard line types: continuous thick for visible outlines, continuous thin for dimensions and hatching, dashed for hidden edges, chain for center and cutting planes, phantom for alternate positions.

A-series sheet sizes

ISO A0 is 841×1189 mm; each subsequent size halves the previous area: A1 594×841, A2 420×594, A3 297×420, A4 210×297 mm.

Title block contents

A title block records drawing number, title, scale, date, drafter, checker, projection symbol, and any general tolerances or notes required to interpret the drawing.

Bill of materials

A tabulated list of parts in an assembly giving part number, description, quantity, and material; it is placed above the title block or on a separate sheet.

Flowchart symbols

Oval for start or end, rectangle for process, diamond for decision, parallelogram for input or output, and arrows to show the direction of flow between steps.