Layer height, infill, walls and supports: which settings matter for a functional part
Most slicer settings change how a print looks or how long it takes. A handful decide whether a functional part survives: which way the layers run, how many walls it has, then infill. This guide ranks them, gives starting points for brackets, enclosures and clips, and uses the names of the options in SpeakCAD's online slicer.Rank the settings before you touch them
For a part that has to hold, clip or close, the settings matter in roughly this order:
- Orientation, because it decides which way the layers run.
- Walls, the cheapest strength there is.
- Material, covered in print settings by material.
- Infill, which matters less than most people expect.
- Layer height, which changes looks and time far more than strength.
- Supports and adhesion, which decide whether the print succeeds and how much cleanup it needs, not how strong the part is.
Speed comes last. It changes time and surface finish, and the printer's own limits cap it anyway.
Orientation: which way the layers run
A printed part is a stack of layers fused together, and the bond between layers is weaker than the plastic along a layer. A hook printed standing up tends to break along a layer line at the bend; the same hook printed on its side carries the load along the layers.
The online slicer's Optimise the orientation option turns the part to its flattest base and fewest overhangs. That is the right call for a print that succeeds, and often for strength too, but not always. For a bracket, a hook or a clip where you know the direction of the load, switch it off: the part is then sliced the way it sits in the file. If that is the wrong way round, export the STL lying the right way. To tell whether the slicer rotated a part, compare the printed height in the result with the model's own height.
Walls: the cheapest strength
Walls (wall loops in OrcaSlicer, perimeters in PrusaSlicer, wall line count in Cura) are the solid outlines of every layer. Bending and twisting loads are carried mostly by the outer material of a part, so an extra wall adds more strength per gram than extra infill. Screws grip walls too: self-tapping screws and heat-set inserts hold much better with three or more walls around the hole.
The Walls option offers the profile default or 2 to 6. Most stock profiles print two. For functional parts:
- 2 walls: light enclosures, trays, covers.
- 3 walls: general parts and anything with screws.
- 4 to 5 walls: brackets, hooks, mounts, parts that take a steady load.
- 6 walls: rarely worth it. If a part needs that much, the design wants thicker sections or a fillet.
Each wall is one more loop around every outline on every layer, so the time it adds depends on the part's outline, not its volume. The result of each slice gives the print time; compare before you commit.
Infill: less than you think
Infill fills the inside with a sparse pattern. It holds up the top surfaces and resists crushing, but past about 25 to 30% it adds strength slowly compared with walls. Common starting points:
- 10 to 15%: enclosures, covers, display pieces.
- 15 to 25%: general functional parts.
- 30 to 50%: brackets and parts under a steady load.
- 100%: small parts that take a lot of force in a small volume, such as spacers.
A section thinner than two sets of walls is solid anyway, so infill changes nothing in a thin clip arm. The infill pattern comes from the print profile. Time and filament grow with the percentage, and the grams on the result tell you by how much.
Layer height: looks and time, not strength
The Print profile sets the layer height from the printer's own presets, usually between 0.08 and 0.28 mm on a 0.4 mm nozzle. Halving the layer height doubles the number of layers and roughly doubles the print time. Within the usual range, layer height changes strength far less than walls and orientation, so do not choose fine layers to make a part stronger.
Choose 0.12 to 0.16 mm for small text, shallow curved tops where steps would show, threads and small snap features. Choose 0.24 to 0.28 mm for big boxes and brackets that nobody inspects closely. 0.20 mm is the default for a reason.
A larger nozzle is the other lever: a 0.6 mm nozzle lays a thicker line per wall and prints large functional parts faster. Select it in Nozzle only if it is the one installed.
Supports: print success, not strength
Supports offers Auto (only where needed), Always and Never. Auto generates supports only where an overhang is steeper than the print profile allows, and the result tells you whether any were printed and how much they weigh. The profile's limit is usually well past 45°, so Auto often lets a 50° overhang print in the air. Always puts supports under every overhang past 45°, small ones included: choose it for PETG, ABS or a printer that droops on overhangs, or for a part whose overhangs must keep their exact shape. Support style is Tree (less material, easier to remove) or Normal (grid), which is steadier under large flat overhangs. Only from the build plate keeps supports off the part's own surfaces, which also keeps them out of horizontal holes and side cutouts.
Supports cost material, time and cleanup, and leave a rougher surface where they touched. The better fix is usually the part: a flat base, chamfers instead of ledges. Why does my print need supports? explains the 45° rule and how Auto decides.
Adhesion and speed
Adhesion: Auto adds a brim when the part needs one. Choose Brim for ABS and ASA, tall parts on a small base, and parts with sharp corners that tend to lift. Skirt draws loops around the part to prime the nozzle without touching it. None prints nothing extra.
Speed: Normal uses the profile's speeds. Quiet runs the wall, infill, top and support speeds at 0.6 times, for a finer surface and a quieter printer. Fast runs them at 1.3 times, capped by the printer's and the filament's limits, and acceleration, travel moves and the minimum time per layer do not change, so the print time drops by less than the factor suggests. Fast is fine for drafts and test fits; for a part that must be accurate, stay on Normal.
Starting points by part
| Part | Walls | Infill | Print profile | Notes |
|---|---|---|---|---|
| Wall bracket, shelf support, hook | 4 to 5 | 30 to 50% | 0.20 mm | Print it on its side so the load runs along the layers; PETG if it gets warm |
| Enclosure, box, lid | 2 to 3 | 10 to 15% | 0.20 mm (0.16 mm for text on the lid) | Open side up; Only from the build plate keeps supports out of port cutouts |
| Clip, snap fit, latch | 3 or more | Any | 0.16 to 0.20 mm | Print the arm lying flat; PETG or nylon flexes without cracking |
| Knob, spacer, small high-load part | 4 | 50 to 100% | 0.16 to 0.20 mm | Brim if the base is tiny |
| Test fit coupon | Same as the final part | Same | Same | Change nothing, or the test tells you nothing |
Compare two slices before you print
Every slice reports the print time, the filament in grams and meters, the layer count, the printed height and the supports. Re-slicing the same file with other settings within 10 minutes spends nothing, so it takes a minute to see what 5 walls instead of 3, or 0.16 mm instead of 0.20 mm, does to the clock. Open the online slicer with your part and try it; the online slicer page lists every option and printer. To weigh time and cost before you slice, without an account, the print time and cost calculator runs the same slicer and returns the numbers only, with the filament and electricity cost.
Settings cannot rescue a design with 0.8 mm walls or a hook without a fillet. The wall thickness guide and the design rules cover the geometry, and when the part itself has to change, SpeakCAD's AI editor rebuilds the STL as an editable model and makes the change you describe.