3D Printing · File Preparation · Beginner’s Guide
From CAD to Print:
A Beginner’s Guide to
File Preparation
File preparation is where most 3D printing problems start — long before the machine does anything. Once you understand what’s happening under the hood, most failures become straightforward to prevent.
Understanding file formats
The default format. Converts your model into triangles. Carries no scale info — always verify units on export.
Supports colour and texture. Useful for visual models; no advantage over STL for functional parts.
Modernised STL. Retains scale, units, colour, and multi-material data. Use it if your slicer supports it.
2D vector format — belongs in laser cutting, not 3D printing. Sometimes used to extrude 2D geometry in CAD.
Designing for printability
CAD software lets you design things that are geometrically perfect and physically unprintable — and it won’t warn you. Know these constraints before you finalise anything.
Wall thickness
- FDM: min 1.2mm, ideally a multiple of nozzle diameter (0.4mm typical)
- Resin: walls under 0.8mm become brittle and warp during post-cure
Overhangs & supports
- Features overhanging more than ~45° need support structures
- Use chamfers and gradual slopes to eliminate supports
- Consider designing tearaway geometry vs auto-generated supports
Tolerances & fit
- A 10mm CAD hole often prints slightly undersized
- Add 0.2–0.3mm clearance to mating dimensions for FDM
- Always print a test peg-and-hole before a full run
Scale & units
- STL carries no unit info — mm vs inches is a silent 25× mismatch
- Check units every export — it takes 5 seconds and saves hours
FDM vs resin: different rules
FDM file prep
- Layer height: 0.2mm standard, 0.1mm for finer detail
- Infill: 15–20% visual, 40%+ structural
- Orientation affects strength, finish, and supports
- More perimeters = stronger part
Resin file prep
- Supports are never optional — poor placement fails prints and damages FEP film
- Hollow large models; add 2–4mm drain holes for uncured resin
- Calibrate exposure for each resin brand and printer model
Common mistakes
Non-manifold geometry
Holes in the mesh, overlapping faces, inverted normals. Fix with Meshmixer, Netfabb, or PrusaSlicer’s built-in repair.
Unit mismatch on export
Metres vs millimetres is the classic one — especially coming from architectural or civil engineering software.
Ignoring print orientation
FDM parts are weakest along Z. Orient so the load runs parallel to layers, not against them.
Designing to exact tolerances
Snap-fit parts designed to exact CAD dimensions almost never work on the first print. Prototype, measure, adjust.
Skipping the slicer preview
Step through the layer-by-layer view before every job. Missing walls and bad supports show up here — before they waste filament.
Free software to get started
The team at GeoSaffer works with clients across New Zealand — from single prototypes to batch production through Plastixel, with file review built into every job.
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