STL, 3MF, OBJ or STEP: which file?
Four formats can be supplied. They differ in what the file contains:
- STL: the most widely used format. The shape is made of small triangles. It contains no units; the size is read in millimetres.
- 3MF: a more modern format that also stores the unit, and often colours and multiple parts.
- OBJ: like STL, a mesh of faces, widely used in modelling and scanning software.
- STEP (.step or .stp): the format of CAD software. It describes the exact shape, with true curves instead of triangles. Useful if the design still needs changes.
Exporting an STL from CAD software? Choose a fine resolution. Otherwise curves and holes turn visibly angular.
Check the size before you upload
A common mistake is the wrong scale: a design in inches read as millimetres, or the other way round. In the quote form, the 3D preview shows the dimensions of your file straight away. If the size is right, the scale is right.
In one piece it can be up to 256 × 256 × 256 mm. Larger is possible in parts, by arrangement.
Wall thickness: not too thin
In FDM printing, the part is built from lines of plastic, about 0.4 mm wide with the usual nozzle. A wall thinner than one such line cannot be printed. As a rule of thumb:
- at least about 0.8 mm (two lines) for a wall that only gives shape;
- 1.2 to 2 mm or more for a wall that carries load;
- pins, hooks and small protrusions preferably no thinner than a few millimetres.
Thicker is not always better. A thick wall takes more material and print time, and ABS and ASA are less suited to large, solid parts.
Tolerances and clearance
A printed part always deviates slightly from the design. Holes often come out a little smaller and pins a little thicker. If two parts have to fit together, give them clearance:
- about 0.2 to 0.3 mm per side for parts that should slide together loosely;
- less clearance for a tight fit; test it first with a small test piece;
- a hole that has to be exact, for example for an axle or bearing, can also be drilled out after printing.
Not sure whether something fits? State in your request which dimensions matter. Your file is checked before printing; if something does not fit, you hear about it in advance.
Overhangs and supports
A printer builds up layer by layer, from the bottom up. Parts that stick out far with nothing underneath need supports. As a rule of thumb, a slope up to about 45 degrees prints without supports. Supports are removed after printing and can leave a rougher surface in that spot.
A 45-degree chamfer instead of a flat ceiling, or a horizontal hole shaped like a teardrop, often prints without supports.
Print direction determines strength
A printed part is strongest along its layers and weakest between them. A hook printed upright snaps off more easily than the same hook printed flat on the bed. The print direction is therefore a trade-off between strength, surface and supports.
Does a direction or side matter, because force acts on it or because that side has to look good? Put it in the note with your file.
Layer height and details
The standard layer height is 0.20 mm; finer is possible by arrangement. A smaller layer height gives smoother curves, but takes more print time. Small details, such as text, come out sharper when designed slightly larger or deeper.
Small errors in the file, such as a hole in the model, are repaired free of charge where possible. More about 3D printing your file.