3D Printing by the Numbers: Layer Heights, Tolerances, Infill and Wall Thickness

3D printing is usually described in terms of what it can make, but the quality and cost of a printed part depend on a handful of settings and measurements. Understanding them makes it much easier to brief a designer, compare quotes and judge whether a part will do its job.

Layer height: detail versus speed

Parts are built up in layers, and layer height has a big influence on both finish and print time. On common FDM printers, layers are typically around 0.1 to 0.3 mm. Thinner layers give smoother curves and finer detail but take longer, because the printer has to lay down more of them. Resin printers can work with much thinner layers, which is why they are often chosen for highly detailed models.

• 0.1 mm: fine detail and smoother surfaces, but slower
• 0.2 mm: a common balance of quality and speed
• 0.3 mm: quick drafts and larger, simpler parts

Tolerances and fit

No printing process is perfectly accurate. For FDM, dimensions are commonly within around 0.2 to 0.5 mm of the design, and holes often print slightly smaller than drawn. Parts that need to slide, clip or press together need clearances designed in, and those clearances are easiest to get right with a test print. That is one reason rapid prototypes are so valuable: a quick first version shows exactly how the fit behaves before the final part is made.

Infill and wall thickness

Most FDM parts are not solid. The outer walls are printed solid, while the inside is filled with a lattice known as infill. A display model might use 10 to 20% infill, while a functional bracket might use 40% or more, sometimes up to fully solid. Wall thickness matters just as much: thin walls can be fragile or fail to print, so designers often work to a minimum of around 1 to 2 mm in structural areas.

Getting these figures right is part of the design, not an afterthought. Professional 3D design takes account of loads, wall thickness and print orientation, which can make a printed part considerably stronger without using more material.

Orientation and strength

FDM parts are strongest along their layers and weakest between them. A bracket printed lying flat may be far stronger than the same bracket printed standing up. Orientation also affects how much support material is needed and how good the visible surfaces look, so the best orientation is always a balance.

Five numbers worth asking about

1. Layer height: chosen to suit the detail needed.
2. Tolerance: and the clearances designed into moving or mating parts.
3. Infill percentage: matched to the load the part will carry.
4. Wall thickness: especially around holes and fixings.
5. Build size: and whether larger parts will be printed in sections.

A few settings make the difference between a part that looks right and one that works. For more on comparing manufacturing and fabrication work, see our manufacturing category.