What size file is too big?

Most STL files under 50 MB are fine. Above 100 MB they get slow to handle — reduce mesh resolution if you can while keeping detail.

Can my maker fix a broken file?

Yes, usually. Most makers can repair common mesh issues, sometimes with a small fee for complex repairs. Sending a clean file is faster and cheaper.

Do I need to design supports?

No — slicers generate supports automatically. Just send the geometry of the part itself.

How to Prepare a File for 3D Printing

Step-by-step file prep for 3D printing — repairing meshes, choosing units, exporting STL/3MF/STEP and what makers actually want.

A good file makes for a good print. Most quoting delays and re-prints come from preventable file problems: wrong units, broken meshes, missing detail or files that don't match the part you actually wanted. Here's how to send your Australian maker a file they can print first time.

Step 1 — Use the right format

STL is universal and what most makers expect. 3MF is better (it carries colour, units and metadata) and increasingly preferred. STEP is best for engineering parts because it preserves true CAD geometry. OBJ is fine but rarely necessary. See our STEP vs STL vs OBJ guide for the full comparison.

If in doubt, export 3MF and STEP and let your maker choose.

Step 2 — Get the units right

STL files don't carry units — a '50' could be 50 mm or 50 inches. Most slicers assume millimetres. Always design and export in millimetres, and tell your maker explicitly in the job description: 'Designed in mm, expected size ~120 × 60 × 20 mm.'

3MF carries units, so this problem disappears if you use it.

Step 3 — Check the mesh is watertight

A printable mesh has to be 'manifold' — every edge belongs to exactly two faces, with no holes or flipped normals. Free tools like Microsoft 3D Builder, Meshmixer or PrusaSlicer's repair feature can fix most issues in one click. If your slicer complains about your STL, run a repair before sending.

Step 4 — Orient and scale sanely

Place the part flat-side-down at the origin (Z=0) so the maker can see how you intend it to print. If a specific orientation matters for strength or finish, say so in the job notes.

Double-check overall size in your CAD before exporting. Slicers and viewers can scale a model accidentally.

Step 5 — Send useful context

Along with the file, tell your maker: the intended material (or 'please recommend'), where the part lives (indoor/outdoor/car/wet), expected loads, the most-important dimension (e.g. 'the hole must be 8.0 mm to fit a bolt'), and the finish you want (sanded, painted, raw).

A 30-second screen recording with measurements drawn over the part is incredibly useful and almost no one sends one.

Step 6 — Multiple parts

If you have several different parts in one job, export each as a separate file with a clear name (top-bracket-v2.stl, base-plate-final.stl). Don't combine them into one mesh — that makes it harder for the maker to slice and to quote.