# Slicing a non-closed mesh - extrude only on faces, no volume

I have a seemingly unique problem. I'm trying to design models that print with single extrusion walls and are not closed volumes. For example, a topographical map model printed on an edge. It has height and width, but no depth. I want the model to print with a single, non-closed extrusion per layer. Printing back and forth as it moves up the model.

When slicers cut up a model, historically each plane must result in a closed shape. The slicer then determines the tool path to create that shape. But what if, instead of a closed shape, the slice results in lines. No area or volume, just lines. Couldn't the slicer then create a tool path at each line?

Is there anything like this available anywhere?

Also, to be clear, I've been doing this 3D printing thing for a long time and know pretty well how slicers work and their resulting models. I've also been 3D modelling for a long time.

The simplest solution I can think of would be to modify a slicer or find a plugin or something that already does what I'm looking for. The second possible solution would be to find 3D software that can "extrude" an arbitrarily complex surface in such a way that normal slicing software with the "detect thin walls" setting enabled would result in a single extrusion resulting in the desired outer surface. I haven't found either in my searching.

The solution should work with nearly any extrusion width or any nozzle. You have a 0.4mm nozzle, you can print the part with wall widths anywhere from ~0.4mm wide to around 1mm. Your choice when slicing. If you have a 1mm wide nozzle, you could print the part with much thicker walls. It would be configurable in the slicer because the model only defines the surfaces, no volume data.

Like I said, this is a seemingly unique problem.

Use Cura to slice and check out the "Surface Mode" option (might be hidden by default; if so, search for and unhide it). Also known as magic_mesh_surface_mode. The "Surface" choice sounds close to what you want and might suffice.

• This sounds very promising! Thanks for the pointer. I'll check it out! Sep 20 '21 at 15:53
• Yes, this is what I want! I've been looking for something like this for so long and now you've found it for me! So exciting! Sep 20 '21 at 17:30

If you are designing a model that has single extrusion walls, you are constructing a design which has volume. A single extrusion wall will be dependent on the nozzle diameter and extrusion multiplier. For the sake of discussion, consider the theoretical nozzle 0.4 mm with a true 0.4 mm extrusion and a 0.2 mm layer thickness.

Your design should reflect this fact. You can/should design your non-dimensional lines to be 0.4 mm wide and 0.2 mm thick in whatever manner you use to create models.

Slicer settings can be adjusted to permit single extrusion walls. A common example is vase mode, in which the printer is directed to construct a single extrusion wall in a specified pattern, usually with an appropriately thick base.

The caveat in this case is that the model file was created to match these requirements. It will be represented as a solid with a thickness to the wall appropriate to the nozzle size.

If you create test models representing a small sample of your overall project and slice them with your preferred slicer, you can examine the resulting g-code, or use the preview feature common in slicers to determine if your objective is accomplished.

In summary, every 3D printed model has all three dimensions. This cannot be avoided, other than in a virtual/simulated environment.

• You see, I don't care what the volume of the resulting print is, I only care about the surface I model. So no, I'm not designing a model with a volume, but a model with a surface. Yes, the resulting printed model will have a volume, but I'm not designing it. Conceptually, it is quite simple to take a non-closed model, and put an extrusion such that the surface of the extrusion matches the model surface, using the face normal to determine which side of the model surface the extrusion is placed. The extrusion thickness setting in the slicer can be used to determine the offset of the tool path. Sep 20 '21 at 1:01

You can also have a look at Chisel, it basically does what you want - creates G-code directly from parametric patches (Bezier, Nurbs), you have fine control over extrusion width in every part of your model (perimeter, infill...).

It's optimised for efficient structural panels so currently always expects 2 faces + infill configuration (could be none for hollow structure), but I will very soon add features like specifying arbitrary number patches with no infill, that way you will have full freedom to design part however you like.