"Not watertight." "Non-manifold edges." "Model has holes." Your slicer, or another add-on, will not take the model. Print Fix finds what is wrong, repairs a copy, and checks the copy again before it tells you it is printable.

What you get

• Check Model. Lists everything that can stop a print: open edges (holes), non-manifold edges, flipped faces, inside-out solids, solids buried inside solids, faces that pass through each other (like Suzanne's eyes), models with no volume, plus loose parts and duplicate vertices. It also reports the thinnest wall and how many faces are under your limit.
• Make Printable. Repairs a copy from gentlest to most drastic: remove loose parts, weld, fix face direction, remove fins, fill holes, drop buried solids, exact boolean union of intersecting shells, and only if you allow it, a voxel rebuild. It stops at the first step that gives a printable mesh.
• It checks its own work. Every result is re-tested. It only says "printable" when the copy passes every check; otherwise you get a message saying what is still wrong and nothing is created.
• Safe by design. The original is hidden, never changed. One click on Discard Fixed Copy brings it back. A model that was already fine comes back unchanged, and a real cavity inside a hollow model is kept.
• Select Problem Edges in Edit Mode, so you can repair by hand when you would rather.
• Works with Bed Fit Splitter (sold separately): it refuses models that are not watertight, so repair first, then split.

See it work

The download includes a 300 mm Suzanne damaged the way real models are. Check Model reports 110 open edges, 1 non-manifold edge, 32 flipped-face edges and 163 intersecting faces. Make Printable takes about a second and the copy passes every check ("no problems found"). Its volume is within 0.04% of the same model undamaged. Dense meshes are fine: a 600,000 face model with holes was repaired in about 20 seconds.

Tested

28 automated tests (each defect type built on purpose, exact volumes, the original never modified, hollow models kept, dense meshes, units) plus a full buyer-path test of this exact download: installed from the zip into a clean Blender, sample imported, checked, repaired, and passed on to Bed Fit Splitter. Run on Blender 4.2.9 LTS and 5.1.2.

Who it is for

Anyone sending Blender models to a 3D printer, especially models imported from STL files, sculpts, or models assembled from separate pieces.

Who it is not for

• You want a large missing area or a strongly curved hole rebuilt beautifully. Holes are filled with flat triangles; the result is watertight, not sculpted.
• You want thin walls thickened automatically. Print Fix reports them but does not change the design.
• Your model is a flat sheet with no thickness. It tells you to add thickness first.

Honest limits

• The voxel rebuild is a last resort and loses detail below the voxel size. You can switch it off, and a rebuild that would change the volume by more than 3% is refused.
• Overlapping shells are merged into one solid. If you wanted separate parts, split the model first.
• No overhang, support or orientation checks; your slicer does those.
• Tested on Linux. It is plain Python on Blender's own libraries, so Windows and macOS should behave the same, but I have not run them yet (untested on Windows and macOS).
• STL files have no units and Blender's default scene counts one unit as one metre. Set 1 Blender unit = 1 mm when you import an STL (the add-on reminds you if a model looks absurdly large).

Requirements

Blender 4.2 LTS or newer. Nothing else to install. Includes a step-by-step guide (HTML), the damaged sample model, and the add-on (GPL-3.0-or-later, like most Blender add-ons: use it commercially, modify it as you like).

Free updates to v1.x. Questions or a model that misbehaves: message us through Superhive or open an issue at https://github.com/RoseCompanion/print-fix/issues.

Also by us: Bed Fit Splitter, Print Fix, Asset Preflight.