A fillet is like a rounded corner but on the inside of the corner.

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


If your part needs structural support, then the word is: absolutely. 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 stress riser 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.

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    $\begingroup$ Chamfers (flat corner cuts) are a better option for printability, unless the corner is in the XY plane. $\endgroup$
    – Trish
    Jun 16 '19 at 18:46
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    $\begingroup$ @Trish - chamfers are not really any more printable than a fillet In my (admittedly limited) experiance, and they still leave two stress points. $\endgroup$
    – SiHa
    Jun 18 '19 at 10:40
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    $\begingroup$ Please check out Makers Muse on fillets & chamfers. $\endgroup$
    – Trish
    Jun 18 '19 at 11:38
  • $\begingroup$ @SiHa Fillets are less printable than chamfers (depending on the printing plane), please read this answer. $\endgroup$
    – 0scar
    Nov 15 '19 at 8:03

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.

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.

  • $\begingroup$ So the nozzle can keep it's speed around corners better, and X-Y fillets are better than Z fillets. Kewlio. $\endgroup$
    – user77232
    Jun 16 '19 at 16:13

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