Whether a model prints comes down to the path you picked at the start and four numbers: wall thickness, overhang angle, clearance and scale. Here are the ranges to design against and the checks to run before slicing.
A model that looks correct in a viewport and a model that comes off the build plate are often two different objects. Printability is decided by a small set of numbers, namely wall thickness, overhang angle, clearance and scale, and by one decision taken before any software is opened: which modelling path you follow.
This tutorial covers the four paths, the tolerance and geometry rules that decide whether a file survives slicing, and the handoff to a slicer, with a symptom list for the failures that show up in the first print.
One question sorts most projects: does the finished part have to mate with something else at a fixed size? A bracket for an M4 bolt or a lid that clicks onto a box is a parametric CAD job, because the dimension is the requirement. A creature or a bust has nothing to dimension and belongs in a sculpting tool; a shape you can describe but cannot sketch is where generative tools earn their place. When a photograph is your only reference, you are on the photo-to-3D path.
In Fusion 360, FreeCAD, Onshape or OpenSCAD the model is a recipe: a 20 mm bore stays 20 mm when the wall around it changes. A printed part rarely fits on the first attempt, and changing one parameter beats re-sculpting a surface. Measure the mating feature with calipers, not a nominal size, and build the clearance into the sketch. Export STL or 3MF at roughly 0.05–0.1 mm surface deviation, or STEP when someone else will edit the file.
Blender, ZBrush and Meshmixer handle faces, fur, cloth folds and armour with organic edges. Sculpt at high resolution, then reduce before printing: decimate to a sane triangle budget and remesh so the surface density is even, because the slicer walks every triangle. Two things decide the outcome. The sculpt must close into a solid volume with no open boundary, and the thinnest feature has to clear the wall thickness rule below. Fingers, spikes and hair strands are the usual offenders.
With a common 0.4 mm nozzle, one FDM perimeter is roughly 0.42–0.45 mm of extruded plastic, too thin to be a wall on its own. Practical ranges: 0.8 mm for a wall that only has to look closed, 1.2 mm for a part a hand will grip, 2.0 mm and up when it carries load or takes a screw. Resin goes thinner, with 1.0–1.5 mm comfortable for a hollow figure; walls below roughly 0.6 mm warp during the cure. Detail finer than the nozzle width disappears, so leave about 0.5 mm of relief on embossed text.
Clearance is the gap you add deliberately between two printed surfaces. It is a process result, not a material constant: the extruder rounds outer corners, the first layer squashes outward and the plastic shrinks as it cools, so a nominally zero gap prints as an interference fit. The values below are starting points; print a stepped coupon in 0.05 mm increments for the fit you need.
| Fit | FDM gap per side | Resin (SLA) gap per side |
|---|---|---|
| Press fit, assembled once | 0.05–0.1 mm | 0.03–0.08 mm |
| Snug fit, pushed by hand | 0.15–0.2 mm | 0.08–0.12 mm |
| Sliding fit, light force | 0.25–0.3 mm | 0.12–0.18 mm |
| Free fit or printed hinge | 0.4–0.5 mm | 0.25–0.35 mm |
| Threaded hole, M3 to M8 | 0.2–0.3 mm extra | 0.15–0.25 mm extra |
A slicer needs a closed surface: every edge shared by exactly two triangles, every normal pointing outward. A mesh can look sealed on screen and still be non-manifold, with T-junctions left by a boolean, duplicate vertices along a seam, normals flipped inside a drilled hole, or a zero-thickness plane left by a cut. Cura, PrusaSlicer, OrcaSlicer and Bambu Studio attempt repair on import, the 3D-Print Toolbox add-on in Blender flags non-manifold edges before export, and Meshmixer can rebuild a solid from a messy surface. Self-intersections are a separate failure that slicers resolve differently.
Photogrammetry in Meshroom or RealityCapture rebuilds geometry from many overlapping photographs and keeps real proportions and texture. Generative image-to-3D predicts a plausible solid from one image or a few views, the only option when the reference is one old photograph. In Open3DAI both paths run through the available engines: one local procedural engine plus optional third-party adapters you connect with your own API keys, and the same image can go through several engines so the meshes can be compared before export. Exports cover GLB, glTF, OBJ, STL, PLY and 3MF. What this does not provide is a dimensioned parametric solid: expect a dense triangle mesh at an arbitrary scale, often with a rounded underside that needs a flat cut and a wall thickness check, and watertight output is not promised.
Engine availability, credit pricing and third-party adapter terms change between releases. Check the vendor page and the current adapter list before committing a budget, and treat a downloaded slicer profile as a starting point, not a validated process.
None of these rules replaces a test print. A printed part is a negotiation between the shape you want and the shape the process can hold, so write the numbers down before you model. Keep the source file too: the STL is an output, and the editable CAD or sculpt file is the asset.
On FDM with a 0.4 mm nozzle, treat 0.8 mm as the floor for a closed-looking wall, 1.2 mm for anything a hand will grip, and 2.0 mm or more when the part carries load or takes a screw. Resin parts are comfortable around 1.0–1.5 mm, and walls below roughly 0.6 mm tend to warp and stay flexible.
Typical starting points are 0.05–0.1 mm per side for a press fit that goes together once, 0.15–0.2 mm for a hand-assembled snug fit, 0.25–0.3 mm for a sliding fit, and 0.4–0.5 mm for a free fit or a printed-in-place hinge. Resin usually needs about half of that. Print a stepped test coupon in 0.05 mm increments before trusting any of these numbers on your machine.
It can generate a plausible solid, but print-ready is a separate step. Generative image-to-3D returns a dense triangle mesh at an arbitrary scale, often with a rounded or hollow underside, and it does not promise watertight geometry. Plan on scaling it to a real measurement, cutting a flat base, checking wall thickness and repairing non-manifold edges before slicing. A part with a critical dimension still belongs in parametric CAD.
Both work in Cura, PrusaSlicer, OrcaSlicer and Bambu Studio. STL stores only triangles, with no units, colour or print settings, so scale is easy to get wrong. 3MF keeps units, multiple objects, colour or material assignments and sometimes process settings, which makes it the better choice for assemblies and multi-colour prints.
Send the same prompt or image to several engines, compare the meshes side by side, then export GLB, glTF, OBJ, STL, PLY or 3MF. Creating an account grants free credits and needs no card.
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Four routes to a figure mesh, the repair pass a slicer quietly expects, and the resin versus FDM decision, with typical numbers for scale, wall thickness and layer height.