CAD glossary: design and manufacturing terms

3

3MF

Modern file format for 3D printing. Unlike STL, it contains units, multiple parts, colours and often print settings. Design for 3D printing →

A

Assembly

A CAD file in which several parts are positioned and connected to each other, so the whole product can be checked. Machine and agricultural parts →

B

B-rep

Boundary representation – the way a solid model is described in CAD, with exact faces, edges and vertices. STEP and Parasolid are based on B-rep. STL to STEP and model repair →

Bend radius

The inside radius of a bend in sheet metal. A common guide value is an inside radius roughly equal to the sheet thickness. Sheet metal and photo etching →

Bill of materials (BOM)

A list of all parts in an assembly with quantity, description, material and part number. Technical drawings →

C

Calliper

Measuring tool for external, internal and depth dimensions. Digital callipers typically read to 0.01 mm. Spare parts without drawings →

Chamfer

An angled bevel on an edge, for example 0.5 × 45°. Makes assembly easier and removes sharp edges.

Collision check

A check in an assembly that parts do not overlap, even when moving parts are moved. Machine and agricultural parts →

D

Datum

A face, axis or point from which other dimensions and tolerances are measured. Datums are often labelled A, B and C on the drawing. Technical drawings →

DfAM

Design for additive manufacturing – designing a part for 3D printing, taking overhangs, orientation and layer build-up into account. Design for 3D printing →

DFM

Design for manufacturing – adapting a design so it is simple and cheap to make with the chosen method. Design for injection moulding →

Draft angle

A slight taper on faces in the direction of mould opening so the part can release from the tool. A common guide value is 1–2°. Design for injection moulding →

DXF

Common 2D format for profiles. Used for laser cutting, waterjet cutting, plasma cutting and sheet metal. Should be at 1:1 scale and in millimetres. Sheet metal and photo etching →

F

Fit

The relationship between a hole and a shaft: clearance, transition or interference fit. Specified to ISO 286, for example H7/g6. Machine and agricultural parts →

Fixture

A device that holds a part in place during machining, assembly, gluing or inspection, so every part ends up in the same position. Jigs and fixtures →

Flat pattern

The flat shape of a bent sheet metal part, cut out before bending. Calculated from the bend radius and K-factor. Sheet metal and photo etching →

G

Geometric tolerance (GD&T)

Tolerances for form and position, such as flatness, perpendicularity and position, given in a feature control frame to ISO 1101. GD&T stands for geometric dimensioning and tolerancing. Technical drawings →

I

IGES

Older exchange format for CAD geometry. Handles surfaces well but solids less well. STEP is usually preferable. STL to STEP and model repair →

Infill

How much of the inside of a 3D-printed part is filled with a pattern, given as a percentage. Affects weight, time and strength. Design for 3D printing →

Involute profile

The curved shape of the teeth on most gears. It makes the teeth roll against each other with a constant gear ratio. Machine and agricultural parts →

IP rating

Enclosure rating under IEC 60529 stating protection against dust and water. IP65, for example, means dust-tight and protected against water jets. Electronics enclosures →

ISO 2768

Standard for general tolerances. Part 1 gives the classes f, m, c and v for dimensions without their own tolerance on the drawing. Technical drawings →

IT tolerance grade

The number in an ISO 286 tolerance, for example 7 in H7. It gives the size of the tolerance – the higher the number, the larger the tolerance. Machine and agricultural parts →

K

K-factor

A value stating where the neutral axis lies in bent sheet metal. Used to calculate the flat length, typically 0.3–0.5. Sheet metal and photo etching →

L

Loft

CAD feature that creates a shape between two or more profiles, for example a transition from a round to a square duct.

M

Mesh

A 3D model that describes the surface with triangles, as in STL and OBJ. Good enough for 3D printing but cannot be edited precisely. STL to STEP and model repair →

Module (gears)

Size measure for teeth on metric gears: the pitch diameter divided by the number of teeth. Gears that mesh must have the same module. Machine and agricultural parts →

N

NDA

Non-disclosure agreement that prohibits the recipient from disclosing information about an idea or design. Inventors and patents →

O

Overhang

Part of a 3D print that sticks out with nothing underneath. Up to about 45° usually works without support material. Design for 3D printing →

P

Parametric model

A CAD model driven by dimensions, constraints and a history of features. Changing one dimension updates the whole model.

Parasolid

Geometry kernel and file format (.x_t, .x_b) used by several CAD programs. Gives clean solids when exchanging between them. STL to STEP and model repair →

Parting line

The line where the two mould halves meet in an injection moulding or casting tool. It often shows as a thin edge on the finished part. Design for injection moulding →

Photo etching

A process in which thin sheet metal is etched chemically through a photo mask. Gives very fine, burr-free features, for example nameplates, meshes and precision parts. Sheet metal and photo etching →

Prototype

An early version of a part or product used to test function, form or assembly before series production. Product development and prototypes →

R

Reverse engineering

Recreating a CAD model from an existing physical part, by measuring, photos or scanning. Reverse engineering →

Rib

A thin reinforcement that makes a wall stiffer without making it thicker. Common in injection moulded and 3D-printed parts. Design for injection moulding →

S

Shell

CAD feature that hollows out a solid to a uniform wall thickness, for example to turn a solid body into an enclosure. Electronics enclosures →

Sink mark

A sunken spot on the surface of an injection moulded part, often where the wall is too thick, for example behind a heavy rib. Design for injection moulding →

Snap fit

A flexible hook that locks two parts without a screw. Common in plastic enclosures and lids. Electronics enclosures →

STEP

Standard format for solid CAD models to ISO 10303 (.step, .stp). Read by almost all CAD programs and workshops. STL to STEP and model repair →

STL

The most common format for 3D printing. Describes the surface with triangles and has no units, colour or material. STL to STEP and model repair →

Surface roughness Ra

Arithmetic mean deviation of a surface profile, given in micrometres. Ra 3.2 µm corresponds to a normally milled surface. Technical drawings →

Sweep

CAD feature that moves a profile along a path, for example for pipes, hoses, mouldings and spirals.

T

Thread gauge

Measuring tool with toothed blades to determine the pitch of a thread, for example 1.25 mm or 20 threads per inch. Reverse engineering →

Threaded insert

A metal sleeve with an internal thread that is heat-set or pressed into plastic. Gives a screw joint that survives many assembly cycles. Electronics enclosures →

Title block

The field in the corner of a drawing with title, drawing number, revision, material, scale and general tolerance. Laid out to ISO 7200. Technical drawings →

Tolerance stack-up

Dimensions placed one after another so that the tolerances add up. Avoided by dimensioning from a common datum. Technical drawings →

W

Wall thickness

The thickness of material in a part. In injection moulding it should be uniform, and in 3D printing ideally a multiple of the extrusion width. Design for injection moulding →