Wall Thickness

What wall thickness means

Wall thickness is the distance between the two faces of any wall in a part: the side of a box, the shell of a housing, the web between two holes. Every process has a minimum below which a wall will not form, will warp during the build, or will break in use. That minimum is a limit, not a target. Most parts work best well above it.

Design guides split walls into two kinds. A supported wall joins other walls on two or more sides, like the side of a box. An unsupported wall joins on fewer than two sides, like a fin or a tab. Unsupported walls have nothing to brace them, so give them extra thickness or a rib.

Minimum and recommended thickness by process

These are starting points, not guarantees. The real limit depends on the machine, the material, the height of the wall, and the load it carries. Treat the minimum as a floor and check anything critical with a test part.

FDM: think in extruded lines

An FDM printer builds each wall from lines of melted plastic called perimeters, each roughly as wide as the nozzle. A feature thinner than one line cannot print at all, and a wall that falls between whole numbers of lines prints less cleanly than one that divides evenly.

Formlabs gives 1 mm as the FDM minimum and suggests 1.2 mm on a 0.4 mm nozzle, because 1.2 mm divides into three whole lines. BigRep's rule of thumb is 2 to 3 times the nozzle diameter. Walls, not infill, form the main structure of a printed part, so for parts that carry load, add perimeters before anything else.

SLA: thin is possible, but fragile

Resin printing makes the thinnest walls of the common 3D printing processes. Formlabs lists 0.2 mm (0.008 in) as the minimum for both supported and unsupported walls on its current printers. It also notes that results vary by machine: its Form 3+ offers more design freedom than the older Form 2 because a flexible resin tank lowers the peel forces during printing.

A 0.2 mm wall survives printing, but not much else. Thin resin walls are more likely to creep and crack once the supports come off, and photopolymer resins tend to be more brittle than thermoplastics. BigRep suggests 0.6 to 1 mm for small display models and 1.5 to 2 mm for functional prototypes. Keep resin walls as uniform as you can, because sudden changes in thickness can warp or crack during curing.

CNC: walls have to survive the cutter

A machined wall is the material left behind after the cutter clears both sides of it. Thin walls are weak and vibrate as the tool passes, which costs accuracy. A common guideline for metal parts is a minimum of about 0.8 mm (0.031 in).

Height matters as much as thickness. The taller a thin wall, the more it flexes under the cutter, so keep tall walls thicker or brace them with ribs. Deep pockets create tall walls, and end mills have limited reach: a common guideline keeps pocket depth within about 3 to 4 times the cutter diameter.

Thicker is not always better

Extra thickness has costs too. Formlabs notes that overly thick printed walls cost more, take longer to print, and can crack, and BigRep lists warping and internal stress as symptoms. Where a wall needs to be stiffer, a rib often does the job with less material than a thicker wall.

Checks before you upload

• Find the thinnest wall in CAD before you export. Most CAD tools have a wall thickness analysis.
• Recheck scaled models. Details that work at full size can become too thin when a model is scaled down.
• Round FDM walls to a whole number of extruded lines.
• Keep walls as uniform as the design allows, especially in resin.
• Thicken or rib tall walls, long unsupported spans, and freestanding tabs.