FDM 3D Printing: The Complete Part Preparation Checklist

Orient critical features perpendicular to the load direction

Layer bonds are the weakest point. Tensile loads parallel to layers will cause delamination.

Keep overhangs under 45° from vertical — or plan supports

Beyond 45°, unsupported material sags. Design chamfers or self-supporting angles wherever possible.

Minimum wall thickness: ≥ 1.2 mm for FDM (ideally a multiple of your nozzle diameter)

A 0.4 mm nozzle prints walls best at 0.8 mm, 1.2 mm, 1.6 mm etc. Thinner walls may not slice correctly.

Add a 0.2–0.4 mm tolerance to all mating holes and press-fit interfaces

FDM parts shrink slightly during cooling and holes come out undersized. Always test-print a calibration piece first.

Avoid fully enclosed voids — leave a drain or vent hole

Trapped air during printing can cause delamination or pressure buildup in the part.

Replace sharp internal corners with fillets (≥ 0.5 mm radius)

Sharp corners concentrate stress and are often under-extruded. Fillets improve both strength and print quality.

Keep tall, thin features short or add a rib/gusset for stability

Tall thin columns oscillate during printing and cause layer misalignment (also known as "ringing" or "ghosting").

Export in STL (binary preferred) or 3MF format

3MF preserves colour, scale and slicer metadata. STL is universally compatible. Avoid OBJ for FDM — it lacks watertight guarantees.

Set export units to millimetres and verify scale in the slicer

An STL exported in inches will appear 25.4× larger. Always confirm dimensions after import.

Check that the mesh is watertight (manifold) — no open edges or holes

Use Meshmixer, Netfabb or PrusaSlicer's built-in repair tool to detect and fix mesh errors.

Remove internal geometry, duplicate faces and intersecting bodies

Boolean unions in CAD don't always export cleanly. Inspect in a mesh viewer before slicing.

Verify surface normals are all pointing outward

Inverted normals cause slicers to misinterpret solid regions as voids, resulting in missing walls.

Set STL export resolution: chord deviation ≤ 0.01 mm, angle ≤ 0.5°

Too coarse and curved surfaces look faceted. Too fine and the file is unnecessarily large with no quality gain.

Layer height: 0.1–0.15 mm for detail; 0.2 mm for standard; 0.3 mm for speed

0.2 mm is the best all-round choice for most functional parts. Use 0.1 mm only for visible cosmetic surfaces — it triples print time.

Perimeter/wall count: minimum 3 for structural parts, 2 for visual prototypes

Perimeters carry most of the load in an FDM part. For high-stress parts use 4–5 perimeters and reduce infill instead.

Infill density: 15–20% for aesthetics; 40–60% for functional; 80%+ for load-bearing

Gyroid and cubic patterns are most efficient. Rectilinear is fastest. Grid is weakest in diagonal directions.

Enable supports only where necessary — prefer self-supporting design

Support interfaces at 0.2 mm Z-gap improve removal. Use tree supports (auto) for organic shapes.

First layer: 0.2–0.3 mm height, 100–110% line width, bed temperature +5–10 °C

A well-calibrated first layer is the single biggest factor in print success. Level your bed and run a Z-offset calibration before each new material.

Bed adhesion: brim (5–8 mm) for tall parts; raft for warping-prone materials like ABS/ASA

Brims are easy to remove and work for 90% of cases. Rafts add significant print time but are worth it for ABS on unheated beds.

Print speed: 40–60 mm/s for quality; up to 200 mm/s on modern printers with input shaping

Reduce speed for overhangs, bridges and the first layer. Quality degrades before the printer physically fails.

Enable cooling fan at 100% for PLA/PETG; 20–40% for ABS/ASA; 0% for PC/Nylon

Insufficient cooling causes stringing and drooping overhangs. Too much cooling on crystalline polymers (Nylon, PC) causes layer delamination.

PLA — visual prototypes, low-stress parts, indoor use only

Easy to print. Biodegradable. Brittle above 60 °C. Do not use near heat sources or in outdoor environments.

PETG — functional parts, light mechanical loads, food-safe applications

Tougher and more heat-resistant than PLA (up to ~80 °C). Slightly stringy — reduce retraction and lower print speed by 10–15%.

ABS / ASA — high heat, impact resistance, outdoor UV exposure (ASA)

Warps significantly — requires enclosure, high bed temp (100–110 °C) and no cooling fan. ASA is a direct upgrade over ABS for outdoors.

TPU — flexible parts, gaskets, grips, vibration dampers

Disable retraction or minimise it (0.5–1 mm). Print slowly (20–30 mm/s). Shore hardness 95A is a good all-rounder.

Nylon (PA12) — high mechanical strength, wear resistance, hinges

Absorbs moisture aggressively — dry filament at 70 °C for 8–12 h before use and print from a dry box.

Carbon-fibre composites (CF-PLA, CF-PETG, CF-Nylon) — stiffness-critical parts

Requires hardened steel nozzle (0.4 mm minimum). Brittle in the Z-axis. Excellent specific stiffness for lightweight structural components.

Store all filaments in sealed bags with silica gel between uses

Moisture-absorbed filament produces bubbles, poor layer adhesion and stringing. A food dehydrator at 50–65 °C dries most filaments in 4–6 h.

Let the part cool completely on the bed before removal — do not force it

Forcing a hot part off the bed causes warping and can crack the first layers. For stubborn adhesion, cool the bed to 20–25 °C.

Remove supports carefully with flush cutters and needle-nose pliers

Support scars are normal. Work from multiple directions and avoid prying against delicate walls.

Measure critical dimensions with calipers before declaring success

FDM parts are typically accurate to ±0.2–0.3 mm. If tighter tolerances are needed, machine critical interfaces or post-process with a drill/tap.

Sand progressively: 120 → 240 → 400 → 800 grit for cosmetic surfaces

Wet sanding above 400 grit gives the smoothest results. Always sand parallel to layer lines to avoid highlighting them.

Apply filler primer (spray) and re-sand at 400 grit for paint-ready surfaces

2–3 thin coats of filler primer fill layer lines more effectively than heavy sanding alone. Let each coat fully dry (1 h) before re-sanding.

Anneal PLA/PETG parts (60–70 °C for 1–2 h) to relieve internal stresses

Annealing improves dimensional stability and slightly increases heat deflection temperature. Use a food oven — parts may deform slightly so compensate in the model.

Thread metal inserts (M3–M5) using a soldering iron for bolt connections

Heat-set inserts provide 3–5× stronger threaded connections than printing threads directly. Set at ~210 °C for PLA, ~230 °C for PETG.