3D printing glossary
Every term below appears somewhere on a quote, on a material page or in a reply from an engineer here. They are defined in the sense this shop uses them, which is not always the sense a general dictionary would give.
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- FDM (fused deposition modelling, FFF, filament printing)
- Building a part by extruding molten plastic filament through a moving nozzle, one layer at a time. It is the process behind almost every functional printed part, and it is what the great majority of this fleet runs.
- SLA (stereolithography, resin printing)
- Building a part by curing liquid photopolymer with light against a plate that lifts out of a vat. It resolves finer detail than an extrusion nozzle can and leaves a surface that needs no finishing.
- Layer height (resolution, layer thickness)
- How thick each printed layer is. Thinner layers mean a smoother surface and a longer print, and the choice is a trade between the two. This fleet runs 0.12 mm to 0.28 mm on filament, with 0.20 mm as the default.
- Infill (fill density)
- The internal lattice that fills the space inside a part's walls, given as a percentage. It is not solid plastic and it is not empty. Raising it adds weight, time and cost, and beyond a point it adds far less strength than adding a wall would.
- Wall thickness (perimeters, shell)
- The solid skin around the outside of a part, printed as a whole number of 0.42 mm nozzle passes. Walls carry the load in a printed part, so a structural part is better served by another wall than by more infill.
- Support material (supports)
- Scaffolding printed under overhanging geometry so it does not sag, then removed. Removal always leaves a rougher surface than the rest of the part, which is why an overhang designed at 45 degrees is cheaper than one that needs support.
- Build volume (build plate, print volume)
- The largest box a given machine can print inside. A part larger than the biggest machine on the floor is split and bonded rather than refused.
- Watertight (manifold, closed mesh)
- A mesh with no holes in its surface, so it encloses a definite volume. A mesh that is not watertight has no unambiguous volume, which means it has no unambiguous weight or price, so it has to be repaired before it can be quoted or printed.
- STL (stereolithography file)
- The most common 3D printing file format. It stores a surface as a mesh of triangles and nothing else: no units, no colour, no material, no tolerance. That is why an STL is quoted on geometry alone and why the units it was exported in matter.
- STEP (STP, ISO 10303)
- A CAD interchange format that stores true curved surfaces rather than a triangle approximation. It is the better format to send when it exists, because nothing has been thrown away yet.
- Lead time (turnaround, production time)
- The time from an order being confirmed to it leaving the building, separate from courier transit. Printing here runs seven days a week, so production days are consecutive rather than business days.
- Warping (lifting, curling)
- A printed part pulling away from the plate or curling at its corners as it cools, because the plastic shrinks as it goes from molten to solid. It is worst on large flat parts in materials that shrink most, and splitting the part at a designed joint usually removes it.
- Anisotropy (layer adhesion)
- A printed part being stronger along a layer than between two layers. It means orientation is a design decision and not a detail, because the same file printed two ways gives two different strengths.
- Heat-set insert (threaded insert, brass insert)
- A knurled brass sleeve pressed into a printed hole with a hot iron, giving a machine thread. It is the standard answer for any printed part that will be unscrewed more than once.
- Bridging (spanning)
- Printing a horizontal span between two supported points with nothing underneath. Short bridges print cleanly because the extrusion is stretched taut as it lays; long ones sag and want support.
- Post-processing (finishing)
- Everything done to a part after it comes off the machine: support removal, washing and curing on resin, sanding, and any inserts. It is real work and it is part of what a part costs.
Where these come up
Layer height, infill and wall thickness are all settings on the quote form, so they change the price directly. What each one is worth changing is covered under design rules. Which process a term belongs to is under processes, and the materials themselves are on the materials page.
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