# How to prepare a model for 3D printing

A practical checklist before you upload: file format, units, wall thickness, overhangs, tolerances, splitting large parts and the most common mistakes.

## Start with the right file

Our quote calculator accepts STL, 3MF and OBJ files. STL is the most common and works well for a single solid part; like OBJ, it carries no units. 3MF is a better container: it stores the units and keeps the model in one tidy file. OBJ also works, but it is less common for printing.

If your model lives in a CAD program, export the part as STL or 3MF. Other formats, such as STEP, cannot go through the calculator; attach them to a custom request instead and we will tell you what is possible. Files can be up to 50 MB. Send one model per file. A file with several separate parts, an assembly or multi-colour painting is priced by hand instead of instantly.

## Check units and scale

The calculator works in millimetres. One of the most common mistakes is a model exported in the wrong unit: a part drawn in inches arrives about 25 times too small, and one drawn in metres a thousand times too small. After the upload, the calculator shows the dimensions of your model. Look at them before anything else and compare them with the size you expect.

The maximum size of a single part is 256 × 256 × 256 mm. A single part larger than that does not fit and has to be split, which is covered below.

## Wall thickness

Prints are built from lines of plastic about 0.4 mm wide, so walls work best as multiples of that width. A few rules of thumb:

- Walls thinner than about 0.8 mm are unreliable and may not print at all.
- For parts that will be handled, aim for at least 1.2 mm; for parts that carry a load, 2 mm or more.
- Text and relief should be at least 0.6 mm wide and about 0.4 mm tall to stay readable.
- Pins and thin posts break easily; make them thicker than you think you need, or add a fillet at the base.

In the calculator you can also pick the number of walls and the infill. More walls and more infill make a part stronger and also heavier, slower and more expensive.

## Overhangs and supports

Plastic is laid down layer by layer, so each layer needs something underneath it. Surfaces leaning out more than about 45 degrees from vertical start to sag, and a flat ceiling needs support. Short bridges of a few millimetres usually print fine without help.

The calculator chooses supports automatically by default, and you can switch them off. Supports cost extra, leave marks where they touched the part and take time to remove, so the best fix is to design them out:

- Give the part a large flat face that can sit on the plate.
- Replace flat overhangs with chamfers of about 45 degrees.
- Split a complex shape in two so that each half prints flat.

Orientation in the calculator is fixed, so the face you want on the plate should be the bottom of your model.

## Tolerances and fitting parts

A printed hole comes out slightly smaller than drawn, and a printed pin slightly larger. If two parts must fit together, add clearance in the model rather than hoping for a perfect match:

- Press fit: about 0.1 to 0.2 mm of clearance on each side.
- Sliding fit: about 0.2 to 0.3 mm.
- Loose or moving parts: 0.3 to 0.5 mm.

These are starting points, not guarantees. Material, size and the shape of the part all change the result, and small holes shrink more than large ones. If a fit is critical, order a small test piece first and adjust.

## Splitting large parts

When a part is bigger than 256 mm in any direction, cut it into pieces that each fit the plate. Cut where the seam is least visible or where a joint is natural. Add alignment features such as pegs and matching holes, or a dovetail, so that the pieces register correctly when glued. Remember the clearance rule: a peg and its hole need a small gap.

A model that does not fit the plate gets no instant price. The calculator says so and points you to a custom request, where we look at how to split it.

## Common errors

- **Open or non-manifold meshes.** The model has holes, loose faces or edges shared by more than two faces. Most CAD and modelling programs have a repair or check tool; use it before export.
- **Zero-thickness surfaces.** A single sheet with no thickness cannot be printed. Give every surface real thickness.
- **Overlapping bodies.** Several solids that cross each other can confuse the slicer. Merge them into one body.
- **Faceted curves.** An STL exported at very low resolution makes round shapes look like polygons. Raise the export quality, but avoid huge files with millions of triangles.
- **Tiny details.** Features finer than the nozzle simply disappear. Enlarge or simplify them.
- **Wrong orientation of the model.** The part is drawn lying on its side with an awkward overhang. Rotate it so the flattest face points down.

## Before you upload

Go through this short list: the file is STL, 3MF or OBJ; the units are millimetres; the dimensions look right; walls are thick enough; flat overhangs are avoided; fits have clearance; and nothing is larger than 256 mm. If a model passes, the calculator will slice it and show you a price within a few minutes. If something looks wrong, you will see the warning before you commit to anything.

**Upload your model**

Open the quote calculator, add your file and check the dimensions and the price. If something does not fit or looks unusual, send it as a custom request.

[Get a quote](https://nori3d.com/en/quote/)