<p>A fillet is like a rounded corner but on the inside of the corner.</p>

<p><a href="https://i.stack.imgur.com/XDTnd.png" rel="noreferrer"><img src="https://i.stack.imgur.com/XDTnd.png" alt="enter image description here"></a></p>

<p>Does it make a difference (structurally) to use fillets on a 3d printed part?</p>

[{'answer_id': 10273, 'author': 'Pᴀᴜʟsᴛᴇʀ2', 'author_id': 11242, 'author_profile': 'https://3dprinting.stackexchange.com/users/11242', 'pm_score': 4, 'selected': True, 'text': '<p>If your part needs structural support, then the word is: <strong>absolutely</strong>. Fillets provide the added support when you need it. If your part has a meeting line which is sharp - 90° (or perpendicular), there is a natural <a href="https://mechanics.stackexchange.com/q/18183/4152">stress riser</a> in your design. This is a weak spot where a crack can form. If strength is needed and the fillet won\'t interfere with the design, it\'s definitely something you should include with your part. </p>\n'}, {'answer_id': 10278, 'author': 'jpa', 'author_id': 16776, 'author_profile': 'https://3dprinting.stackexchange.com/users/16776', 'pm_score': 3, 'selected': False, 'text': '<p>Fillets in X-Y plane (i.e. between two vertical surfaces) work great for 3D prints and increase the strength a lot. They usually also improve the print quality, because the print head can keep a constant speed in the curve instead of slowing down to a sharp corner.</p>\n\n<p>However fillets that extend in Z direction (i.e. between a vertical and a horizontal surface) suffer from layer artifacts. Sometimes they can look worse than a sharp corner would. While they do still increase the strength significantly, they are not as strong as similarly sized fillets in X-Y plane are.</p>\n'}]
['https://3dprinting.stackexchange.com/questions/10272', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/12857/']