How do you take the 3D model you just downloaded from Thingiverse and convert it to a set of instructions your 3D printer can read? That's a question that baffles many a newcomer to 3D printing. The good news is it's really simple, and you can use free software to do it in just a few minutes.

G-Code is the standard language for most 3D printers, but note that some machines use other formats such as .x3g. In this tutorial we explain how to turn STL files into G-Code printing instructions.

How to convert STL to G-Code using Ultimaker Cura 

It's likely that your 3D printer was supplied with some software such as Cura that facilitates .stl to .gcode conversion, but we recommend downloading the latest version directly from the vendor's website. At the time of writing that's Cura 3.3.1 - download it free here. Double-click the .exe file to install Cura.

How to add printer in Cura

With Cura installed on your computer you need to configure it for your 3D printer. Go to Settings, Printer, Add Printer. You might find your printer is in the list, though ours was not.

We're using a Creality3D Ender 3, a great budget 3D printer that you can buy now from GearBest for just £183.10 (reviewed here). We selected Other, Creality CR-10, entered Ender 3 as the printer name and then clicked Add Printer. 

If you have to manually add a printer, you'll also want to specify the dimensions of your printer bed. Go to Settings, Printer, Manage Printers and, with your model selected, click Machine Settings. We set X and Y to 220mm, and Z to 250mm. Cura will remember these settings, so you won't have to add them each time.

Download or create a 3D model

Now you're ready to bring in a 3D model to prepare for printing. There are dozens of sources online, and you may even choose to create your own in a separate 3D modelling app. We're using Thingiverse as an example, from which you can freely download 3D models in STL format under a Creative Commons licence.

If you choose to download a 3D model from Thingiverse you should find a model and then click the 'Download all files' button. Files are free to download, but you can tip the designer if you like. 

On your computer find the file in the Downloads folder using File Explorer, then right-click it and choose Extract all. You need only the .stl file, which will be in the Files folder. Double-click this file to open it in Cura, or launch Cura and go to File, Open Files and browse to it on your computer.

Prepare your 3D model for printing

In Cura you should click the 3D model to select it, then choose the Scale icon from the menu on the left. Use the options here to specify how large you want the model to be printed. Any changes you make will be applied proportionately. 

Cura Scale 3D model

Over on the right side of the page you'll see you can adjust the layer height, which affects the print speed. If each layer is 0.06mm your model will take longer to build than if each layer were 0.2mm (the default). The smaller the layer height the better the quality; the larger the layer height the lower the quality but the faster the print.

Cura Adjust Quality

When you're ready to 'Slice' the model (prepare it for print) click the Prepare button at the bottom right of the screen. You'll see how long it will take to print the model at those settings, as well as how much plastic the model will use. (Naturally the latter will not change when you adjust the print speed or layer height.)

Cura Slice File

If you want to reduce the print time you should increase the layer height or reduce the size of the model, then click Prepare once again. Otherwise you can go ahead and click Save to file.

Cura Prepare G-Code

Cura will save to your computer a .gcode file that will be recognised by your printer as a set of instructions for recreating that model in 3D. You can now transfer this file to the printer and select it for printing.

Learn more about 3D printing.