Infill density change when changing layer thickness

Hi,
I am experiencing unexpected behavior in Slic3r when I change the layer thickness.
The finer I make the layer the less infill I get. I am not changing the Infill percentage!
0.1mm Layer height gives 50% less infill than 0.2mm. 0.05mm has again 50% less infill
Why is that?

Chipmunk

You will possibly find that the infill percentage (as a volume) has not changed, but the the extrusion width of the infill has increased with the smaller layer height, which means that the infill pattern must be spaced further apart to give the same infill percentage. For example, imagine an infill of 50% with an extrusion width of 0.05mm The lines of infill will be 0.1mm apart to give equal lines and gaps for the required 50% infill. If however the extrusion width is 0.1mm, the infill lines will be 0.2mm apart, which is still 50% infill but will appear to be less dense.

You can easily tell if the infill volume is different. Check the G-code files with a text editor and look for the line that gives the total filament length used. If the filament used is approximately the same for both layer heights, then the infill percentage must also be the same.

Dave

What is your extrusion width set for the infill?

@ Mikk36: The extrusion width for infill is zero
@Dmould: That is not logical, as a thinner layer should result in less material deposited per layer - 0.1 mm should deposit half as much material than 0.2 mm per layer
Otherwise the width of the deposited filament would be doubled for half the layer hight which would result in incorrect dimensions.

Chipmunk

Quote
Chipmunk
@ Mikk36: The extrusion width for infill is zero
@Dmould: That is not logical, as a thinner layer should result in less material deposited per layer - 0.1 mm should deposit half as much material than 0.2 mm per layer
Otherwise the width of the deposited filament would be doubled for half the layer hight which would result in incorrect dimensions.

Chipmunk

Setting a line width of zero means that Slic3r will select an appropriate width to use - you can find out what it has selected by looking at the comments in the G-code files.
The total amount of material used for a print is approximately the same regardless of layer height (for a given infill density). Halving the layer height will halve the amount of material for each layer. If you keep the line width the same but decrease the layer height, there will be half the amount of material deposited per line (because even though the width is the same, the height is less, requiring less extrusion to achieve that width).

If the extrusion width is doubled that will indeed increase the amount of material used *in that line of infill* - which is why there will then be half as many infill lines drawn, thus increasing the spacing between the lines and giving the illusion that the infill is less dense. Increasing the extrusion width or number of the perimeters will increase the total amount of material used (and increase the density of the print slightly because it will have thicker walls) - but that has nothing to do with infill density.

Line width will not affect the finished dimensions - Slic3r calculates the paths so that the outside dimensions are correct no matter what the perimeter line width. Note that perimeter width and infill width are not necessarily the same.

Dave

Dave
That supports my statement: If I ONLY change the layer hight, why does that change the density of infill pattern?
By the way Slic3r is the only slicing program that does that and it is not logical.

Chipmunk

What makes you believe that the infill density has changed?

Dave

Because, where I get a nice raster for e.g. 10% infill at 0.2mm layer height, the raster degenerates to just one line when setting the height to 0.05mm and gets near solid when setting 0.4mm height.
At least the preview displays it this way.
Chipmunk

Quote
Chipmunk
Because, where I get a nice raster for e.g. 10% infill at 0.2mm layer height, the raster degenerates to just one line when setting the height to 0.05mm and gets near solid when setting 0.4mm height.
At least the preview displays it this way.
Chipmunk

Just one line? How small is the object? Could you perhaps attach an image showing the paths.

Dave

The dimensions are aproxemately 4x4x8cm
The Pictures are for 0.4mm, 0.2mm 0.1mm and 0.05mm layer height.
Infill density is set to 10%, I changed only the layer height.

Chipmunk

Edited 1 time(s). Last edit at 06/03/2016 12:48PM by Chipmunk.

Infill is 10% on all of those, the extrusion width is changing.
If you don't want it to change automatically, set its value yourself from the Print -> Advanced page.

Ok, thanks, that explains it.

Chipmunk

Yes, the images make it clear that it is exactly the issue I described, and your infill percentage is not changing. As Mikk36 says, set a fixed extrusion width and they will all look the same - the wider the width, the fewer infill lines you'll get.

Dave