Discontinuity in Cura Fill Behavior vs. Fill Setting

[calinb 11]

The photo sequence is:

1. 24% (single layer)

2. 25% (single layer)

3. 25% (two layers)

Note that Cura prints a full hatch pattern per layer at 24% but only "half" a hatch pattern per layer at 25%. More significantly, the overall hatch density increases disproportionately at 25%, compared to the 24% fill setting. I'm trying to obtain a hatch density somewhere between 24% and 25%. Is there a way to do it?

I printed it both ways and the Rep-Host depiction is correct and accurate.

For reference, the grid is the standard Rep-Host grid (10 mm).

Thanks!

 

[illuminarti 18]

Yes, this is a known behavior. At around 25% (it's related to the bead-to-gap spacing ratio, iirc) Cura changes from doing both directions on a layer to only doing one direction at a time. The spacing gets closer together then to maintain the volumetric infill percentage, given that in any given direction, every other layer is empty. i.e., the closer spacing is needed to ensure that 25% of the internal volume still contains plastic, taking into account that the vertical density is now half what it was.

 

[owen 19]

Not sure what you're trying to do Cal but I know that 25% is the cut off point in Cura where it changes from cross hatching on the same layer to cross hatching on 2 layers.

[calinb 11]

Thanks, guys.

Regardless of whether Cura does both directions per layer or only one direction, I'd like the final cross-hatch density to be roughly half-way in between the 24% and 25% settings. Just eyeballing the diagonals on the grid, Cura approximately doubles the hatch density from about 2-3/4 cross hatch lines / diagonal (14.14mm) to about 6 cross hatch lines / diagonal (or ~5.1 mm spacing to ~2.4 mm spacing. I'd like to print something with around 3 or 4 mm spacing.

This is a manufacturing die that must withstand pressures somewhere in the range of 100 to 500 psi. I'm printing nylon for its chemical resistance, strength and, to some extent, the desirable properties of flexibility and compressibility. However, I must balance the compression of a sparse hatch density against the significant propensity of printed nylon to warp. Cura doesn't seem to support the "sweet spot" that I need.

Like support, there's always the option to just design the cross hatch into the model (and I've found this to be necessary for support in Cura nylon prints), but it's nice when a slicer can produce these features automatically, as necessary.

 

[illuminarti 18]

Yes, I agree that it would be nice to have more control over the spacing: having something in the range that you're looking for would be useful; the wider gaps can be a bit too wide for easy bridging, while the close ones are unnecessarily close.

[gr5 2,178]

For this very specific need I recommend Cura 13.04 or a different slicer all together (like kisslicer).

Older versions of cura here:

http://software.ultimaker.com/old/

Cura switched to a whole new slicing engine at version 13.05 so version 13.04 or older will do a good job with your infill. You can choose hex infill, or other patterns. Or the default "random lines" pattern.

 

[calinb 11]

Sure--I have Kisslicer Pro and I use all the slicers, including netfabb. They all have their strengths and weaknesses. Cura is now the fastest slicer, but it is currently lacking features (speed and limited feature set both being related to the newness of the core engine, I'm sure). Kisslicer is unreasonably fault-intolerant of model imperfections. My models are often very complex and it's impossible to process very complex models in Kisslicer without some weirdness occurring somewhere in the gcode. Netfabb is very buggy and poorly supported by its commercial owner (which I've mostly learned to workaround) and it can produce unacceptable inaccuracies in dimensions (it's "Pythagorean-challenged" when printing on a diagonal, for example) but it offers the most control off all the slicers by far. Slic3er provides an average of all the other slicer's traits.

That's my very brief summary of slicers, as I see them. This model has about 100,000 triangles, which isn't too bad, and the old Skeinforge Cura will probably be my next choice, even though it will take a lot longer to slice than with Steamengine Cura.

 

For this very specific need I recommend Cura 13.04 or a different slicer all together (like kisslicer).

Older versions of cura here:

http://software.ultimaker.com/old/

Cura switched to a whole new slicing engine at version 13.05 so version 13.04 or older will do a good job with your infill. You can choose hex infill, or other patterns. Or the default "random lines" pattern.

 

[calinb 11]

For sure, but at least PA6 and 618 nylon bridge large gaps wonderfully!

 

Yes, I agree that it would be nice to have more control over the spacing: having something in the range that you're looking for would be useful; the wider gaps can be a bit too wide for easy bridging, while the close ones are unnecessarily close.

 

[Daid 306]

Right now the code works like this, the distance between infill lines is calculated for the line infill. This distance is between the center-line of the lines. If this distance is more then 4x the extrusion width then it does the grid infill at double that distance.

This logic was made to prevent the grid infill from happening at high densities, because at high densities the corners of the grid would get too much material and cause problems. If 4x distance is the best option, I'm not sure. I just picked something that made sense in my head.

There is always the battle between fine grain control and ease of use. I'm still pondering to make the main logic of the slicer scripted, so you can tweak things like this at will...