3D Printing and CNC Glossary

3D printing terms

FDM (fused deposition modeling)

A 3D printing process that melts plastic filament in a heated nozzle and lays it down line by line, building the part one layer at a time. It is also called fused filament fabrication (FFF), because FDM is a Stratasys trademark. More on FDM 3D Printing

SLA (stereolithography)

A resin 3D printing process that uses light to cure liquid photopolymer resin into solid plastic, one thin layer at a time. SLA gives smooth surfaces and fine detail, and parts are washed and post-cured after printing. More on SLA 3D Printing

Slicer

Software that turns a 3D model into instructions for a printer. It cuts the model into layers, plans the walls, infill, and supports, and writes the result as toolpaths, usually in G-code.

Layer height

The thickness of each layer a 3D printer lays down. Thinner layers show finer detail on curves and slopes but take longer to print. More on Infill and Layer Height

First layer

The layer printed directly onto the build plate. Everything else is built on it, so a first layer that is uneven or poorly stuck often leads to warping or a part that comes loose.

Perimeter (wall)

One of the outline paths that form the outer and inner walls of each layer in an FDM print. The number of perimeters sets the wall thickness, and more perimeters usually make a stronger part. More on Wall Thickness

Infill

The internal structure printed inside an FDM part, set by a pattern, such as grid or gyroid, and a percentage from 0% (hollow) to 100% (solid). Infill mainly holds up the top surfaces; the walls carry most of the strength. More on Infill and Layer Height

Nozzle

The heated tip that extrudes melted filament in an FDM printer. Its diameter, 0.4 mm as standard on desktop printers, sets the width of each printed line and the thinnest wall the printer can make. More on Wall Thickness

Build plate

The surface a print is built on, also called the print bed or, on a resin printer, the build platform. FDM build plates are usually heated to help the first layer stick.

Brim

Extra loops printed around the base of a part on the first layer. A brim enlarges the contact area with the build plate to improve adhesion and resist warping, and is removed after printing.

Raft

A disposable base of several layers printed under a part, which is then built on top of it. A raft helps parts with small or uneven footprints stay stuck down, then peels away after printing.

Supports

Temporary structures printed under overhangs and other features that would otherwise start in mid-air. They are removed after printing and leave marks where they touched the part. More on Overhangs and Supports

Overhang

Any part of a model that extends outward over empty space. In FDM, surfaces that lean up to about 45 degrees from vertical usually print without supports; flatter overhangs need them. More on Overhangs and Supports

Bridging

Printing a horizontal span across open air between two supported points, such as the roof of a slot. Short bridges print without supports; long ones sag. More on Overhangs and Supports

Stringing

Fine hairs of plastic left across gaps in an FDM print when molten material oozes from the nozzle as it travels between areas. It is reduced with retraction and temperature settings and mainly affects appearance.

Warping

Distortion caused as printed plastic cools and shrinks unevenly, most often seen as corners lifting off the build plate. Materials that shrink more as they cool, such as ABS, warp more than PLA.

Anisotropy

Having different properties in different directions. FDM parts are anisotropic: like wood, they are stronger in one direction than another, and weakest when a load pulls the layers apart.

Resin vat (resin tank)

The container of liquid resin in an SLA printer. Light passes through its clear bottom to cure each layer, and the part is pulled away from the bottom as the build platform rises.

Post-curing

The final step for SLA parts. After uncured resin is washed off, parts are exposed to light and heat so the resin finishes curing and reaches its full material properties.

CNC machining terms

CNC machining

A subtractive process in which computer-controlled cutting tools remove material from a solid block, called stock, to make a part. CNC stands for computer numerical control. More on CNC Machining

G-code

The most widely used programming language for CNC machines and 3D printers. Each line tells the machine where to move, how fast, and along what path.

Toolpath

The route a cutting tool or print nozzle follows. CAM software generates toolpaths for machining, and a slicer generates them for printing.

End mill

A rotating cutter with cutting edges on its end and its sides, and the most common tool on a CNC mill. Flat, ball-nose, and corner-radius end mills leave different shapes at the bottom of a cut.

Spindle

The rotating shaft of a machine tool that holds and drives the cutter. Spindle speed is measured in revolutions per minute (RPM).

Feed rate

The speed at which the cutter advances through the material, usually given in millimetres or inches per minute for milling. With spindle speed, it sets how much material each cutting edge removes per turn.

Setup

Each time a part is clamped in a new position or orientation on the machine. Features that cannot be reached from one side need another setup, and each extra setup adds time and cost.

Fixture (workholding)

The vice, clamps, or custom fixture that holds a part rigidly while it is machined. A design with flat, accessible faces to grip is quicker and more accurate to hold.

Internal corner radius

The rounded inside corner left by a rotating cutter. An end mill cannot cut a sharp vertical inside corner, so internal corners carry at least the tool's radius, and a radius slightly larger than the tool gives a better surface.

Burr and deburring

A burr is a small raised edge or sliver of material left on a part after cutting or drilling. Deburring removes it, so edges are safe to handle and mating parts seat properly.

Files and CAD terms

STL

A common mesh file format for 3D printing that describes only the surface of a part as a list of triangles. It stores no colour, material, or units, so the software that opens it has to assume the units. More on STL File

STEP

A neutral CAD format, defined in ISO 10303 and saved as .step or .stp, for exchanging exact solid models between CAD systems. Unlike STL, it keeps true curves, which makes it the usual choice for CNC machining. More on STEP File

Mesh

A 3D surface made of many small flat polygons, usually triangles. STL, OBJ, and 3MF files store meshes, so curved surfaces become many small flat facets. More on 3MF File

Tessellation

Converting exact CAD surfaces into a mesh of triangles, which happens whenever a model is exported to STL. A coarse export turns round holes and curves into visible flat sides, so check the export resolution. More on STL File

B-rep (boundary representation)

The way CAD programs and STEP files describe a solid: by its bounding faces, edges, and vertices, defined with exact surfaces such as planes, cylinders, and splines rather than triangles. More on STEP File

Watertight (manifold) mesh

A mesh that fully encloses a volume, with no holes, gaps, or stray internal faces, so every edge is shared by exactly two triangles. Slicers need a watertight model to tell inside from outside.

Bounding box

The smallest rectangular box that fully contains a part, given as length, width, and height. It is the quick check for whether a part fits a printer's build volume or a machine's working area.

Chamfer

A flat, angled cut across an edge, often at 45 degrees. On printed parts, a 45 degree chamfer on an edge facing the build plate prints cleanly without supports, where a fillet starts as a steep overhang.

Fillet

A rounded edge or corner. Fillets spread stress, and inside corners on machined parts get one from the cutter anyway; on printed parts, fillets facing the build plate start almost flat and print poorly.

Draft

A slight taper on faces so a part can release from a mould or die, typical of moulded and cast parts. Printed and machined parts do not need it.

Measurement and quality terms

Tolerance

The permitted variation in a dimension, written as a range such as 10 mm ±0.1 mm. Tighter tolerances take more time to make and check, so they belong only on features that need them. More on Tolerances and Fits

Fit

The designed relationship between two mating parts, such as a shaft in a hole. A clearance fit leaves room to move, an interference fit grips, and a transition fit sits between the two. More on Tolerances and Fits

GD&T (geometric dimensioning and tolerancing)

A symbolic language on engineering drawings and 3D models for controlling form, orientation, and location, such as flatness, perpendicularity, and position, relative to datums. It is defined in ASME Y14.5 and in the ISO GPS standards.

Datum

A theoretically exact point, line, axis, or plane used as the reference for dimensions and measurement. Good datums match the faces a part locates on when it is in use.

Surface roughness (Ra)

A measure of the fine texture of a surface. Ra is the average deviation of the surface profile from its mean line, given in micrometres (µm) or microinches.

First article inspection (FAI)

A full check of the first part from a new or changed production process against every requirement on the drawing, to confirm the process makes conforming parts. In aerospace it follows the AS9102 standard.