Musings and Experiments on the Art and Science of 3D Printing


KISSlicer 1.6: Fractional Loops - Lunacy or Brilliance?

By Michael Hackney Saturday, September 9, 2017
Now that you have the new KISSlicer 1.6, did you notice the tool tip when you mouse over the Num Loops field on the Style panel? If not, here it is:

Fractional loops!!? "What the heck is that?" you might be asking yourself. You're in luck, I'm going to tell you what it is and explain why this is a brilliant and powerful new feature unique to KISSlicer 1.6!

As the tool tip says, if you enter a fractional value for number of loops (aka perimeters), KISS will add an additional loop "periodically". Here's how it works...

Let's take a simple case and enter 3.5 for fractional loops. This tells KISS to generate 3 loops but 50% (the .5) of the time, add a 4th loop. So, on average, you'll get 3.5 loops in your print. Here's a cut-away drawing to show what this looks like:
The upper drawing labeled 3 Loops illustrates a part sliced with a normal 3 loops - this is what other slicers and KISS 1.6's ancestors do. Now look at the lower drawing labeled 3.5 Loops. See what's happening? See why this is a brilliant new feature? With fractional loops, the resulting overlap with the infill significantly improves bonding of the infill to the perimeter - similar to a finger joint in woodworking. The simple butt joint shown in the upper drawing is a weaker joint by comparison. Here is what the g-code paths look like for a part sliced with 3.5 loops. If you look carefully, you'll see the alternating 3-4-3-4 loops (medium blue paths):
Of course, you can enter other fractions like .25, .33, .75 too. Using 3.x loops as an example, these would create the following patterns:

  • 3.25 loops: 3-3-3-4
  • 3.33 loops: 3-3-4
  • 3.75 loops: 3-4-4-4 

Fractional loops - especially .5 fractional loops - is such a useful feature, all of my default styles have .5 fractional loops.

Now you know about this great new KISS 1.6 feature and how it can create stronger printed parts. It's a brilliant feature, use it with your prints!

EDIT 8/20/2017
A few readers have commented that slicers already support an infill overlap feature and that this is functionally the same thing. Here's a short description in the difference and why fractional loops is a more useful and powerful feature:

Infill overlap actually increases the amount of filament that needs to be squeezed into the same volume. Fractional infill does not. For example, if you used a 50% infill overlap - depending on slicer of course since they each handle this differently - you end up with two times more filament in the area of overlap. This excess filament can create other issues - especially on the first layer and top surfaces. The infill overlap feature was originailly intended to compensate for printer mechanical issues and differences and hysterysis in an effort to reduce/eliminate gaps. In a perfect world, the infill would perfectly connect right at the perimeter interface but mechanical slop and a number of other factors prevent this. KISS supports infill overlap too, for exactly this reason. The fractional loops feature provides a more consistent and reproduceable mechanism for increasing the strength of this critical loop-infill interface that works over all infill percentages.

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