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Infill percentage seems crazy

Posted by StlLooking 
Infill percentage seems crazy
March 13, 2018 07:39AM
Maybe I am not understanding what 20% means. I assumed it meant to only take up 20% of the infill-area.

It seems like it might be leave 20% of the infill-area clear.

The image is for 20% Rectilinear. Those are 2mm (yes, Two) square/diamond holes.

Is this something I am doing wrong or is this screwed up?

open | download - infill-20.jpg (69 KB)
Re: Infill percentage seems crazy
March 13, 2018 10:14AM
Then your nozzle must be 0.4mm, because 2mm *20% = 0.4mm.
Re: Infill percentage seems crazy
March 13, 2018 03:56PM
Then your nozzle must be 0.4mm, because 2mm *20% = 0.4mm.

Umm, is that supposed to help me understand what 20% infill means? If so, it is way to obscure, care to elaborate.

I just ran a 10% infill and got squares that are around 7mm. Still not grasping this concept.

I hate to have to use Cura as my selected Slicer, but it does infill in a logical way to this old Engineer's mind.
Re: Infill percentage seems crazy
March 13, 2018 08:02PM
Ignore the squares for now; just think of one layer.

If your nozzle does 0.4mm wide strips across an area, at 2mm intervals, 20% of the area will be filled. (0.4mm/2mm = 0.2 = 20%). You can calculate the interval, given the nozzle width and infill percentage (0.4mm/0.2 = 2mm)

If you're wanting 10% infill, then the calculation is 0.4/0.1 = 4mm intervals. If you're actually getting a 7mm interval, then something is wrong.

Getting back to the squares... there are 2 alternating layers, with strips at right angles to each other. Each layer is 10% full or 20% or whatever, so the whole volume is filled by the correct percentage.

Since the nozzle size is fixed, decreasing the infill percentage increases the interval between extruded material.
Re: Infill percentage seems crazy
March 14, 2018 05:24AM
If you compare 100% to 20% then 20% is 1/5th the material. So if 100% is complete infill (with every print run touching its neigbour) 20% only prints 1 of every 5 runs. So you are not printing 4 runs - a run is (nominaly) a nozle width so for a 0.4 nozle the runs are spaced 4 x 0.4 = 1.6mm apart. If you use auto or set the extrusion width to about 0.48 then the spacing is 4 x 0.48 = 1.92mm.
frankvdh points out that the layers are alternating so no one layer prints a square. The square shape appears after printing at least 2 layers.

Hexagonal does print hexagones on each layer - more time and vibration due to direction changes.
Re: Infill percentage seems crazy
March 14, 2018 06:52AM
@frankvdh and @MCcarman

Thanks for the explanations, it seems overly complex to define when all I want is 20% of the open space to be taken up with plastic. I should not need to do calculations. This method is programmer's esoteric-gibberish and having employed many of programmers in my businesses, I know it well. smiling smiley

The 7mm measured through the top-layers so might have been 5mm or 6mm inside.

By trial and error, I have found that 12% seems a good default to prevent Pillowing but also not waste plastic.
Re: Infill percentage seems crazy
March 14, 2018 07:05AM
Slicer's infill % has always been a little weird. It used to be there was a huge jump in density going from 24 to 25%. It looks like that jump has moved under 20% based on the photos. The 7mm squares at 10% infill seem typical to me.

Whatever the number, you can always look at the rendered gcode using the preview window and make sure the fill density makes sense for the part you're printing.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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