Let's begin with:  USE AT YOUR OWN RISK!!!!

This is version 6 of my brush cutter.  It attaches to a Ryobi 18V String Trimmer (THIS ONE).  It is designed to cut down thicker brush that may grow in your yard, and this version seems to be able to handle large weeds about the diameter of my pinky finger (average adult male).  I did break it when I hit the cedar fence, but it's not meant to take that amount of force.

PRINTING

I recommend printing this at 100% infill.  As long as you don't abuse it, it probably won't break.  You can then sharpen it by  sanding it if it starts getting dull.  Also, 100% infill adds to the rigidity of the design, and you want that.

0.2 mm resolution works just fine.

BONUS:  Here's a video of Version 5, which definitely broke:  https://youtu.be/4e7GXS0hwms

The version 6 brush cutter blades are twice as thick, and it tore through those weeds.