How does 3D printing work? From file to finished part

3D printing turns a digital model into a physical object one layer at a time. Instead of cutting a part from a larger block, the process adds material only where the geometry requires it.

The principle is simple. The result depends on decisions made before the machine starts: model quality, orientation, process, material and production settings.

1. The process starts with a 3D model

The source is usually a CAD or mesh model. It should describe a closed solid with an unambiguous inside and outside. Open edges, intersecting surfaces and accidental internal shells can produce missing or unexpected geometry.

Common input formats include STL, 3MF, STEP and OBJ. STL describes the shape as triangles but carries limited design information. STEP preserves CAD geometry and can be more useful when the part needs an engineering adjustment.

2. Geometry is analysed and oriented

Before production, the model is checked for thin walls, gaps, overhangs, enclosed spaces and support requirements. It is then oriented on the build platform.

Orientation affects:

• strength in different directions,
• surface appearance and layer visibility,
• supports and the marks left after removal,
• production time and material use,
• accuracy of holes and mating surfaces.

There is no universally correct orientation. A project must prioritise strength, appearance, accuracy or cost. Our guide to orientation, layers and infill explains the trade-offs.

3. Slicing turns geometry into machine instructions

A slicer divides the model into hundreds or thousands of horizontal sections. For each layer, it calculates either a toolpath for the nozzle or an area to be cured by light.

This stage defines layer height, wall paths, infill, support structures and material-specific parameters. The result is no longer just a model: it is a production instruction for a particular process and machine.

Decision	Main effect on the part
Layer height	Surface steps, production time and fine shape changes
Wall paths	Stiffness, surface durability and behaviour around holes
Infill	Mass, support for top surfaces and part of the mechanical response
Supports	Printable overhangs, but also marks and finishing time

4. FFF and SLA create layers differently

In FFF/FDM, filament is heated, pushed through a nozzle and deposited as adjacent paths. It is a practical process for prototypes, enclosures, fixtures and many functional parts.

In SLA/MSLA, light selectively cures liquid resin. It can reproduce finer features and a smoother surface, but the part needs washing, post-curing and a resin selected for its actual use.

Read FFF versus SLA if you are deciding between the two.

5. Post-processing is part of manufacturing

The machine finishing its cycle does not always mean the part is ready. Supports may need removing, resin needs washing and curing, visible surfaces may need sanding, and functional holes may require controlled finishing.

A presentation model may need primer and paint. A technical part is more likely to need dimensional inspection, threads, inserts or a fit check. Define the expected finish before quoting, not after printing.

6. Inspection asks whether the part meets its purpose

Inspection covers completeness, critical dimensions, support marks and the agreed use case. For mating or high-value parts, a small test coupon or first article can prevent an entire batch from repeating the same issue.

What to remember

1. 3D printing builds in layers, so direction matters.
2. Material name alone does not guarantee part performance.
3. Supports, layer marks and dimensional variation are natural process considerations.
4. A good file speeds up analysis; a clear use case improves decisions.
5. A test part often costs less than correcting a complete batch.

Next, read about the real limitations of 3D printing or use the model preparation checklist.