PrusaSlicer - Control Slicer stepping
Hi,
I'm looking for a way to control the slicer to approximate my true geometry in a "maximum" approach.
Imagine the stepping of an inclined plane - you could either
- lay all slices centered to the surface
- lay all slices above the surface (approximate "from below" - like the upper sum in Riemann's integral) << This is what I want to do
- lay all slices underneath the surface (approximate "from above" - like the lower sum in Riemann's integral)
This looks to me similar to a scaling by up to half of the slice thickness in Z and half of the extrusion width in X and Y, but I can't seem to find a parameter that's controlling exactly what I described above.
RE: PrusaSlicer - Control Slicer stepping
I don't think what you are asking for is possible with FDM. With FDM you are stacking bricks on top of something: either the bed, support, or the prior part layer. The option you do have for improving the appearance of the steps is to reduce layer height.
RE: PrusaSlicer - Control Slicer stepping
Oh, it seems that I wasn't able to correctly describe what I mean.
Here is an attempt to visualize the three cases (with a slightly bent "true" surface):
RE: PrusaSlicer - Control Slicer stepping
That's a much clearer explanation 🙂 I also didnt have any idea what you wanted to do until those images.
I have never seen any setting anywhere to do anything like that in SlicerPE or Plicer.
RE: PrusaSlicer - Control Slicer stepping
These same principles would apply even to a vertical surface; they just get exaggerated on a diagonal surface. And none of the scenarios you showed in the pictures actually change the aesthetic appearance of the diagonal surface, just its dimensions.
So the question is, exactly what is the problem you are trying to solve?
I haven't looked at the most recent slicer output, but when I looked very closely at the G-code generated by a slicer several generations back, the path of the nozzle was evidently calculated to be centered on the "extrusion width", with the outer perimeter of the extrusion located precisely at the boundary of the model. The extruded trace was apparently assumed to be perfectly rectangular in cross-section. When people make a cube or a cylinder and then tweak their Extrusion Multiplier, they are measuring the dimensions of the cube with calipers, which of course actually measure the peaks, not the average of the perimeter of the object. In other words, if you printed a cube that measured 1cm on a side, measured perfectly with calipers, and then immersed the cube in water (a la Euclid) it would displace slightly less than 1 cubic cm of water due to the slightly oval shape of the traces (as you drew them above).
RE: PrusaSlicer - Control Slicer stepping
If you simply scale up the size of your object in the X/Y direction by double the size of your extrusion width, seems like that would do what you'r wanting?
RE: PrusaSlicer - Control Slicer stepping
I think the topic is worth discussion, but it tends to be esoteric. I've always assumed the slicer is placing plastic to create an edge dimension. I want a cube 25 mm across, and the slicer builds a cube with the outside perimeters spaced such that they are 25 mm apart. How the slicer handles angular build is something I've never really considered; other than an expectation it is similar to how the cube works. But it is a valid question: where on the diagonal line is the layer placed? Top, midpoint, or bottom of the extrusion edge? Middle makes the easier algorithm, but allows size irregularities. Same with using the bottom corner.
With tolerances what they are, a fraction of a fraction of a millimeter isn't going to hurt much, though will affect smaller geometries in a tangible way: like radius of inside hole dimensions for smaller parts like screws (top down view of the same end point question).