Craftsman Computer Aided Mechanical Drawing flashcards

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

A1 sheet size

Under ISO 5457, A1 measures 841 × 594 mm. It is obtained by halving the larger dimension of A0 (1189 × 841 mm) and is a preferred size for mechanical assembly drawings.

First-angle projection symbol

The truncated cone symbol drawn with its small circle on the left of the side view declares first-angle arrangement, where views are placed on the far side of the object from the observer.

ISO 5455 preferred scales

Recommended reduction scales are 1:2, 1:5, 1:10, 1:20, 1:50 and 1:100; enlargement scales are 2:1, 5:1 and 10:1. Non-preferred scales should be avoided on production drawings.

Chain thin line

A thin line of long dashes separated by short dashes. It marks centre lines, pitch circles, axes of symmetry and cutting plane traces, and extends slightly beyond the feature it locates.

Model space versus paper space

Model space contains geometry at full size, one unit equalling one millimetre. Paper space layouts hold the sheet border, title block and scaled viewports for plotting.

Relative polar coordinates

Entered as @distance<angle. The @ marks the offset from the last point and the angle is measured counter-clockwise from the positive X axis, so @50<90 draws 50 units straight up.

Block definition behaviour

A named block is a single reusable definition. Re-editing the definition updates every insertion in the drawing, whereas exploded copies become independent geometry and lose the update link.

Layer freeze versus off

Turning a layer off hides its objects but they are still regenerated. Freezing also hides them but suppresses regeneration, which speeds up work in large drawings.

DXF exchange format

DXF is a documented, largely text-based CAD exchange format that preserves layers, blocks and geometry. It allows drawings to move between different CAD systems without the native DWG format.

Perpendicular bisector construction

With radius greater than half the segment, strike arcs from both endpoints. The two arc intersections define a line that bisects the segment at 90 degrees.

Hexagon from circumscribed circle

Stepping the compass around a circle at a radius equal to the circle radius produces six points. Joining them gives a regular hexagon whose side equals the circumradius.

Tangent perpendicularity rule

A tangent line touches a circle at exactly one point and is perpendicular to the radius drawn to that point of tangency, which is the basis for tangent constructions.

Ellipse four-centre method

A close approximation of an ellipse drawn with four arcs. Centres are found on the axes using the difference between the semi-major and semi-minor axes, giving a smooth ovoid curve.

Involute of a circle

The curve traced by a point on a taut string unwound from a circle. It forms the standard profile of gear teeth because rolling contact between involutes gives constant angular velocity ratio.

Third-angle view arrangement

In third-angle projection the top view is placed above the front view and the right-side view to the right. The view is placed on the same side as the observer.

View alignment rule

Adjacent views share projection lines: front and top align in width, front and side align in height, and top and side align in depth. Misalignment indicates a projection error.

Front view selection

The front view is chosen to show the most characteristic contour of the part, the fewest hidden features, and the part in its normal operating or machined position.

True length condition

A line appears at true length only in a view where the line of sight is perpendicular to it. A line perpendicular to a projection plane appears as a single point.

Hidden line convention

Hidden edges use a dashed thin line. They are omitted where a visible edge or centre line coincides, and are avoided in favour of a section or auxiliary view when clarity suffers.

Limit dimensions calculation

Given 30 with deviations −0.020 and −0.041 mm, the upper limit is 29.980 mm and the lower limit 29.959 mm. Tolerance equals the difference, 0.021 mm.

Hole-basis fit system

The hole is held at a constant tolerance grade and letter, usually H, while the shaft letter and grade are varied to obtain the required clearance or interference. Marked as H7/g6.

Clearance fit condition

A fit is a clearance fit when the smallest hole is larger than the largest shaft, so a gap always exists. Transition and interference fits occur when the tolerance zones overlap or the shaft exceeds the hole.

Maximum material condition

MMC is the largest permissible shaft or the smallest permissible hole, that is, the size leaving the most material. Departing from MMC toward LMC yields bonus geometric tolerance.

Feature control frame order

The frame reads left to right: geometric characteristic symbol, tolerance zone value with diameter symbol if applicable, material condition modifier, then datum reference letters in order of precedence.

Full section view

A view produced by a single cutting plane passing completely through the object. Hatching covers only material intersected by the plane, not surfaces visible behind it.

Half section application

Used on symmetrical parts. One quarter is removed to reveal internal detail while the opposite half retains the exterior, the two halves separated by a centre line rather than a visible edge.

Rib not hatched in section

When a cutting plane passes longitudinally through a thin rib, web or spoke, the feature is not hatched and no visible edge is drawn across it, avoiding a false impression of thickness.

Auxiliary view purpose

An auxiliary view is projected on a plane parallel to an inclined surface, so that surface appears in true shape and size. It is projected perpendicular to the inclined face from a primary view.

Parts list contents

The parts list on an assembly drawing records item number, part number, description, quantity, material or standard designation, and remarks, matching the balloon numbers on the views.

Thread conventional representation

External threads show a thick continuous line at the crest and a thin continuous line at the root, placed about 0.85 of the major diameter. Threaded holes reverse the line weights.

Detail drawing requirements

A detail drawing of one part carries all dimensions, tolerances, fits, surface finish symbols, material, heat treatment, part number and quantity per assembly needed for manufacture.

Paper space plot scale

When plotting from a layout, the plot scale is 1:1 because the sheet is drawn full size. The drawing scale is set by the viewport scale applied to model space geometry.

CTB versus STB plot styles

Colour-dependent plot style tables map each object colour to a pen width and screening. Named plot style tables assign styles independently of colour, decoupling lineweight from drawing colour.

Revision table purpose

A revision table lists revision letter, date, description of change and approver, while clouds and triangles mark changed areas so readers can identify the current state of the drawing.