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I have this wing design that I want to print:

wing

You can notice that its walls have a thickness, which is 1.0 mm. I want to print it so that the perimeters are inside that thickness. Here is the wing sliced with 1 perimeter and 0% infill:

wing detail

You can notice a gap between the perimeters. That gap is what I want filled and not the perimeters in the image. With 0 perimeters and 100% infill I got this zig-zagged line:

Zigzag filled gap between perimeters

I want the gap to be filled; but, I don't want it to be zig-zagged like in the image. I want it to be smooth like the perimeters in the other image.

Basically I want a smooth infill that goes around the curves just like the perimeters. The reason why I don't want to print both the perimeters and the infill is because I want to save as much weight a possible as this is a wing of a model plane that must fly, so the lighter it is the more efficient it will be.

Any ideas how I can slice this?

The images are screenshots in Slic3r, but I can use Cura as well. This is just a test slice. The wing model is not finished yet.

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I found a great solution!

In Cura, there is a setting under Shell called Horizontal Expansion. What this does is it controls the distance between the two perimeters. A negative value in this field will make them come closer together, thus removing the gap between them.

Horizontal Expansion settings dialog

I found that -0.1 is the perfect value for 1 mm thick walls like the ones in my design. So I set it to -0.1, then set the infill to 100% because in some spots the thickness is a little bit more than 1 mm, so the infill closes the gaps in those places. Here is the result:

Image of Solid perimeters

You can see the perimeters are now sticking to each other and there is no gap between them. The result estimated weight is 71 g, which is a quite good reduction from the estimated 92 g when not using horizontal expansion.

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    $\begingroup$ What you're doing here is in effect asking for a 0.8mm wall thickness. The other variable you can adjust is the extruder width you provide to cura (so you might achieve 3 lines making 1mm - but possibly with worse adhesion, since you're under-extruding) $\endgroup$ – Sean Houlihane Jun 4 '17 at 16:08
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Consider to create a test print using the settings you've presented in the sliced output rendering. It could be something as small as a 4 or 5 mm tall cross section, enough to get clear of the bed and establish a stable base. You may find that your goal is achieved.

Also consider that a common nozzle diameter is 0.4 mm and with an extrusion multiplier, you may not reach a clean integer combination. That is to say, a 0.4 mm nozzle and a 1.05 extrusion factor results in (theoretically) a build thickness of 0.42 mm. Take two of those and you have 0.84, but three of them are 1.26 mm.

You can increase number of wall thicknesses or reduce them as needed to avoid infill or the attempt by the printer to create infill. It may be necessary to adjust your model parameters to achieve a clean combination.

I know that Slic3r supports concentric infill, which will effectively trace the walls rather than turn them into zig-zag shapes. On a base layer, having such a pattern may make for a weaker layer, but you can adjust so many things in that respect that you should be able to accomplish your objective.

Experimentation is useful in a situation such as this. What Slic3r shows you isn't necessarily what will hit the bed.

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  • $\begingroup$ still a small gap, even if not visible in the print, might make the 2 perimeters not join well together thus making the part less strong. Also increasing the extrusion multiplier will result in more material extruded, resulting in more weight, so just using both infill and perimeters might result in a final part that is a little bit heavier but much stronger than a part with just the perimeters and a higher extrusion multiplier. $\endgroup$ – Tooniis Jun 3 '17 at 23:47
  • $\begingroup$ You will always have a "gap" in the sliced rendering. The gap is to distinguish one perimeter from another. As noted in the answer, what you see on the screen isn't what you'll get on the print bed. Granted, the zig-zag lines will likely be created as an infill, but if the rendering shows two perimeters and no infill, that's what will print. The print settings will determine how well one perimeter joins another. There are a number of 3D printed RC planes "out there" which means others have been successful. If extreme light weight is your goal, your tools may not be well chosen. $\endgroup$ – fred_dot_u Jun 4 '17 at 0:00
  • $\begingroup$ Oh, yeah, it may be necessary to adjust your inside rib thickness in order to prevent infill and to turn that part of the model into perimeters, but the original suggestion of experimentation applies. Such changes would not likely be easily accomplished within the printer slicer settings, as those changes apply to the entire model and not a particular segment. If you have wing skins of 1.26 mm, three perimeters should meet that specification, but an inner rib of 1.00 mm will fail for the aforementioned reasons. $\endgroup$ – fred_dot_u Jun 4 '17 at 0:03
  • $\begingroup$ Thanks for the explanation. Now I have a better understanding of what you mean. I will perform 1 or more small print tests and report the results. $\endgroup$ – Tooniis Jun 4 '17 at 0:38
  • $\begingroup$ There is definitely a gap between the perimeters in the 3D print. The render is accurate because I have already set the extruder width in Slic3r to match my printer's, which is 0.4 mm. Concentric infill works well for a cylinder, but not for my wing design. $\endgroup$ – Tooniis Jun 4 '17 at 12:03

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