3D printing, laser cutting or CNC milling? Why the process clients ask for is often not the one they need

4 hours ago

5 min read

Many clients come to me with the process already decided. "I need this 3D printed." "Can you laser cut this?" Often that first idea is not the best way to make the part. So before I recommend anything, I ask what the part has to do: carry a load, look beautiful, survive outdoors, be made once or a hundred times, be ready by Friday. The right process follows from the answers. Here is how I decide in my workshop in Berlin.

The short answer

A flat part cut from a sheet, or an engraved surface: laser cutting.

A complex 3D shape, hollow, with internal details or undercuts: 3D printing.

A solid, strong part, true 90 degree edges, very smooth surfaces or a 3D relief in wood or plastic: CNC milling.

Adding material or removing it

The main difference between these processes is simple. 3D printing is additive manufacturing: it builds the part layer by layer and puts material only where it is needed. This is why it can make hollow parts, internal channels and undercuts, with very little waste. The price is that the part is made of layers, which shows on the surface and makes it weaker between the layers.

CNC milling and laser cutting work the other way. They start with a solid block or sheet and remove material until the part is left. The part keeps the full strength and quality of the original material, and the surfaces and edges can be very clean. The limit is that the tool has to reach every surface it shapes, so undercuts and closed cavities are not possible, and the removed material becomes waste.

3D printing: complex shapes, fast changes

I print with FDM technology, which builds the part layer by layer from plastic filament. My printers go up to the size of a Prusa XL, with a build volume of 36 × 36 × 36 cm. My standard materials are PLA and PETG, and other filaments add special properties: TPU for flexible parts, carbon fiber filled filament for extra stiffness, lightweight PLA for light parts, and wood and metal look filaments for a wide variety of finishes.

When it fits: shapes no other process can make, such as hollow parts, internal channels, undercuts and organic forms. Changing the design only means changing the file, which makes 3D printing ideal for prototypes and small series.

Limits: layer lines are visible, and the part is weaker between the layers than along them. Large parts take long, often days. Anything bigger than the build volume has to be printed in sections and joined.

Example: molds for growing mycelium for a laboratory. The set included molds from 10 × 10 × 10 cm up to 25 × 25 × 25 cm, printed in PLA and PETG, and printing took several days. For many different shapes in small numbers, 3D printing is the obvious choice: no tooling, and every mold is simply a file.

Laser cutting: flat parts, clean edges, beautiful engraving

My CO2 laser has a working area of about 100 × 80 cm. It cuts acrylic (Plexiglas) up to 10 mm, wood, MDF, cardboard and paper, and it engraves all of these materials.

When it fits: anything that starts as a sheet, such as panels, signs, light objects and enclosures built from flat parts. Outlines and small holes come out precise, and cut acrylic edges come out clear and polished. Engraving opens great design possibilities: patterns, text and images on wood, acrylic or cardboard turn simple flat parts into eye catching objects.

Limits: the laser only cuts through flat material, so 3D objects have to be assembled from flat parts. Thickness is limited, and in thick material the cut edge is slightly angled rather than exactly 90 degrees. Some materials must never go into a laser: PVC, for example, releases chlorine gas when cut.

Example: a transparent acrylic bar counter with walls to hold the glasses, about 150 × 60 × 50 cm. The design splits the counter into elements that each fit inside the machine and join into one piece. Designing for the machine is half the job.

CNC milling: solid parts, true edges, smooth surfaces

My CNC milling machine works up to 60 × 60 cm, with parts up to about 20 cm high, in plastics, acrylic and wood. A rotating cutter removes material from a solid block or sheet. Unlike the laser, it cuts true 90 degree edges, and unlike 3D printing, it leaves very smooth surfaces.

There are two basic kinds of CNC jobs:

2D cutting: the machine cuts parts out of flat material and can add grooves and pockets. This is quick and suits thick or strong parts that are too much for the laser.

3D milling: the machine shapes a full 3D surface. This takes more time but allows almost unlimited surface shapes, such as reliefs and curved forms.

Limits: CNC milling cannot make undercuts, which 3D printing can. Inside corners always keep a small radius from the round cutter. Every part needs toolpath programming and setup, and the material removed from the block is waste.

Example: a client's 2D logo turned into a 3D relief in natural wood, about 50 × 40 cm. I modelled the relief in 3D and then milled it into the solid board. A laser could only have engraved the surface, and a printer could not have delivered real wood.

Quick comparison

3D printing: complex, hollow and organic shapes, undercuts, prototypes, small series. PLA, PETG, TPU, carbon fiber filled, lightweight PLA, wood and metal look filaments. Up to 36 × 36 × 36 cm. Hours to days.

Laser cutting: flat parts, signs, panels, acrylic objects, engraving. Acrylic up to 10 mm, wood, MDF, cardboard, paper. Up to 100 × 80 cm per sheet. Minutes to hours.

CNC milling: solid parts, true 90 degree edges, smooth surfaces, reliefs. Plastics, acrylic, wood. Up to 60 × 60 × 20 cm. Hours for 2D cutting, longer for 3D milling.

What to send

3D printing: an STL or 3MF file, or STEP if I should adjust the design. STL files carry no units, so tell me the real size. Walls thinner than about 1 mm often fail.

Laser cutting: a vector file (DXF, SVG or PDF) at 1:1 scale, with text converted to outlines, closed shapes and no duplicate lines.

CNC milling: STEP for 3D parts, DXF for 2D contours. For a relief, a vector logo is enough; I build the 3D model.

No file yet? A sketch with dimensions is enough to start.