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3D Printing Design Guidelines: Wall Thickness, Overhangs, Holes and Fits
Most 3D printing problems start in CAD, not on the printer. A wall that is too thin, a hole with no clearance or an overhang with nothing under it can turn a good idea into a failed part, a support-scarred surface or a higher quote. This guide gives you practical design rules for the four processes you will meet most often: FDM , SLA , SLS and MJF .
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The numbers below are typical starting values used across the industry. Machines, materials and part sizes vary, so treat them as safe defaults and check anything critical with your print service before you order.
Quick reference: design rules by process
Rule FDM SLA (resin) SLS (nylon powder) MJF (nylon powder)
Minimum wall (supported) 0.8 mm 0.5 mm 0.7 mm 0.5 mm
Recommended wall 1.2–2 mm 1–2 mm 1–2 mm 1–2 mm
Minimum hole diameter 2 mm 0.5–1 mm 1.5 mm 1 mm
Unsupported overhang About 45° Needs supports below about 30° No supports needed No supports needed
Clearance between moving parts 0.3–0.5 mm 0.2 mm 0.4–0.5 mm 0.4–0.5 mm
Escape holes for hollow parts Not needed 3.5 mm or more 5 mm or more 5 mm or more
1. Wall thickness
Thin walls are the most common reason a file is rejected or a part breaks. In FDM, a wall is built from extruded lines (perimeters). With a standard 0.4 mm nozzle, a 0.8 mm wall is just two lines, which is fine for a cosmetic shell but weak for anything that takes load. For functional parts, aim for 1.2–2 mm .
In SLA, very thin walls can warp as the resin cures, so keep walls of large flat areas at 1 mm or more. In SLS and MJF, thin walls survive printing but can bend during powder removal and cooling, so 1 mm is a safer minimum for anything bigger than your hand.
Tip: keep wall thickness as even as possible. Sudden jumps from thin to very thick sections cause uneven cooling, which leads to warping and sink marks, especially in SLS and MJF.
2. Overhangs and supports
FDM and SLA build parts layer by layer on top of the layer below. When a surface leans out too far, there is nothing to print on, so the printer adds supports. Supports add cost and leave marks where they are removed.
FDM: overhangs up to about 45° from vertical usually print cleanly without supports. Short horizontal bridges (under about 10 mm) are often fine too.
SLA: almost every part needs some supports. Design so the support marks land on surfaces that do not matter.
SLS and MJF: the loose powder supports the part, so overhangs are free. This is a big reason to choose powder processes for complex shapes.
Simple ways to avoid supports in FDM: replace flat ceilings with a 45° chamfer, turn round horizontal holes into a teardrop shape, and split very complex parts into two pieces that print flat and bolt together.
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