Doubts of how the software slice....

  • Regards,

    I have doubts about how the software behaves when I slice a stl to print it ... and also, if everyone does it in the same way, or they do it differently, I have made a scheme so that it can be better understood.
    Let's imagine that I want to print an extrusion of this profile:


    Let's imagine that I want to print in 3D an extrusion of that figure, filament of 1.75 mm and Nozzle 0.4 mm.

    When I prepare that piece to print:

    • The measurements of the printed piece are:
      o A x A and hole diameter D
      o (A-1/2 nozzle) x (A-1/2 nozzle) and hole diameter (D-nozzle) : (A-0.2) x (A-0.2) and hole diameter (D-0.4)
      o (A-1/2 extrusion with) x (A-1/2 extrusion width) and hole diameter (D-extrusion width) : (A-0.24[my profile]) x (A-0.24[my profile]) and hole diameter (D-0.48[my profile])
      o Other: Explain please.

    • All the slicers do the trajectories in the same way?

    In most cases it does not matter ... but in 5% ... sandpaper, drill and / or Dremel ....

    Thanks in advance

  • administrators

    In theory, it's A x A and hole diameter D. However, small holes always come out smaller in practice, for several reasons. Selecting "External perimeters first" or "Outside-in" printing order reduces this effect, but doesn't eliminate it. So get used to asking for larger holes than you actually want.

  • I use single outlines and make all my holes polyholes, see Then they always come out the exact size I want.

  • Hi....

    Something like this?

    Hole slice

  • Yes but you also need to limit the number of sides to about twice the hole diameter in mm.

    When the nozzle turns a corner the filament likes to take a shortcut and cut the corner, making it rounded. When you have a less corners they are further from the desired circle, so when they get rounded they are still outside it. I found empirically that when the number of sides is twice the diameter the rounded corners just about lie on the circle, so you get the roundest hole that is still the right size.

    Since I design exclusively on OpenSCAD it is not problem for me to make all holes with poly_cylinders instead of cylinders. My STL files then print correctly with any slicer and toolchain.

    When printing other peoples designs, my old machines that run from my own host and firmware have the ability to detect circles in the g-code and convert them. That enabled me to print thousands of Mendel parts without having to ream all the holes.

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