Slic3r Semantics. What are all of the consequences when changing certain parameters?

Hello all! I have just assembled my first 3D printer, and am in the middle of trying to calibrate it, but I have a few questions about what is actually happening when changing some of the settings in Slic3r.
Particularly with the following settings:
-Layer Height
-Fill Density
-Extrusion Width
-Extrusion Multiplier

I think I would much better understand how to approach improving my print quality if I understood what exactly is happening at the hot end. For example, If I increase Layer height, I am assuming that the .stl file gets cut into fewer slices as they are all equally thicker, which also means that the z-axis motors move a little bit more for each layer, and the code simultaneously tells the extruder to push out more plastic to build the thicker layer? Is that correct?

If someone with a lot of experience can give me a few explanations, it would be much appreciated. I have found quite a few suggestions on trouble shooting certain problems, but I would like to know how exactly they are solving the problems, as opposed to just following instructions to get to the solution.

Again, much appreciated!

Quote
Xyphota
I think I would much better understand how to approach improving my print quality if I understood what exactly is happening at the hot end. For example, If I increase Layer height, I am assuming that the .stl file gets cut into fewer slices as they are all equally thicker, which also means that the z-axis motors move a little bit more for each layer, and the code simultaneously tells the extruder to push out more plastic to build the thicker layer? Is that correct?

Yes.

Start here: [manual.slic3r.org]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Layer height - you have understood perfectly. Note that it is common practise to make the first layer thicker than the rest, which is advantageous if your build plate is not exactly flat & level and can also help the first layer to stick to the plate. If you design your own parts it is a good idea to keep in mind how you plan to slice the model, and make all vertical sizes such that they are an exact multiple of layer height + first layer height.

Fill density - this affects the density of the fill pattern used in the inner layers. 100% will give you a solid part, while 0% will give you a hollow part. As you decrease the fill percentage the lines of the fill pattern will usually get further apart, though it is also affected by the extrusion width. Higher fill density gives a stronger but heavier part and uses more filament. 100% density is not usually a good idea because any slight over-extrusion (which can occur on different parts of the model) will result in progressively higher bumps that can mess up a print completely. You don't get a great deal of improved strength above about 60% anyway. Slic3r will use solid (100%) infill on small areas - you can set the threshold in the "Solid infill theshold area" under "Print Settings">"Infill" You can also have solid layers at intervals to improve the strength of models with low infill densities. Set this in "Print Settings">"Infill">"Solid infill every N layers" For parts with small layer heights you can also tell Silc3r to print thicker infill every 2 or 3 layers to reduce printing time while still keeping the advantage of finer layer lines on the outside of the part. "Only infill where needed" will create a part that is hollow except where infill is needed to provide support for the structure above.

Extrusion width - this is the width of the line of plastic that is laid down. It can be different for infill & perimeters. Slic3r uses the extrusion width, line length, filament diameter and layer height to calculate the volume of plastic it needs to extrude for each move, and commands the extruder to feed that amount of filament. Widths that are much thinner than your nozzle diameter or thicker than about 1.5 times your nozzle diameter are unlikely to give very satisfactory results. The extruder is also likely to be the limiting factor regarding the max printing speed. The greater the extrusion width and the greater the layer height, the more plastic needs to be pushed through the nozzle for each move. As you increase the print speed it gets to the point where the extruder is not powerful enough to push the required amount of plastic through the nozzle in the required time, so it will start skipping. If you design your own models you should ensure that thin walls are 1, 2 or 3 times the perimeter extrusion width. Above 3 times the extrusion width doesn't matter because it will be printed with infill. If walls are not coming out correctly (missing walls, too thin or hollow) you can usually correct it by adjusting the perimeter extrusion width. Note that the line width is only accurate if it is bounded by a line on each side. A single line of plastic will have bulging, rounded sides and thus be thicker than the set line thickness, which is why I do not agree that the "single wall test" is an accurate way to set the extrusion factor.

Extrusion multiplier - Theoretically this should be fixed at 100% and is not needed so long as you have calibrated your extruder correctly, but in practice your printer may not print the correct extrusion width for a given layer height for a variety of reasons. You can adjust the actual width so that is matches the expected width with this parameter. There are several ways to adjust this, but IMO the best is to print two cubes of about 30mm X 30mm X 5mm. Print the first cube with 50% infill and 3 solid top layers, and the second with 90% infill and no solid top layers. Examine the top surfaces of both cubes under a strong lens or microscope. The first cube should show lines that have no gaps between them, and the second cube should have lines with small but visible gaps between them. If the first cube shows gaps between lines, increase your extrusion factor, if the second cube shows no gaps, decrease your extrusion factor. You may have to tweak it for different filaments, though these days if you buy reputable filaments they have accurate & consistent diameters and so perform the same in that regard. It can also change for different layer heights. After a time you will become adept at detecting over-extrusion or under-extrusion as the part is printing. Some printers allow you to adjust the extrusion factor "on the fly" which has the same effect as doing so from within Slic3r. There is no practical difference between changing the extrusion multiplier and changing the filament diameter.

Dave

Edited 1 time(s). Last edit at 07/11/2016 08:35AM by dmould.

Thanks for your response Dave! Ive been using that information quite a bit over the last 2 weeks. One more thing I am trying to combat is getting accurate diameters on cylindical holes. I am printing a design that has 9.2 mm cylindrical holes, but there finished print has holes that measure 8.4-8.6mm wide. That is 0.6-0.8mm off target and kind of annoying. The perimeter that follows the outside of the shape needs to be 61.0mm and the resulting print leaves me with 60.8-61.0mm so that is pretty damn close. I have been reading up on this online and it looks like it could be a slicing issue, where the path that the hot-end follows results in too much extruded filament on the internal radius of the path's arc.

The issue is described in this article: [reprap.org]

Is there anyway to tackle this issue in the Slic3r settings?

Thanks in Advance!

Yes, the dimensions of curves will not usually be accurate due to a few factors, one being that the inner circumference is smaller than the outside circumference which pushes the extruded plastic toward the centre. You may also get some slight bulging of corners, especially with a Bowden extruder (for a different reason).

The smaller the hole (or column), the greater the inaccuracy. Slic3r has a setting you can use to compensate - go to "Print Settings">"Advanced">"XY Size Compensation" Hover the mouse for tooltips. You are unlikely to get holes of different diameters to all be accurate. In my designs I compensate by making the holes bigger - e.g. to clear an M3 bolt I will use a hole size of 3.4mm or 3.5mm. You can also drill out holes to the correct size after printing. Sometimes it is best to make a small test design in order to find the size that ends up printing as you want it to print by trial-and-error. I've done that with things such as bearing housings and pipe fittings to get a nice tight fit. Another useful technique is to print polygons instead of circular holes - the dimensions of an octagon will be more accurate than the dimensions of a circular hole and often fulfils the required purpose just as well - for small holes an octagon prints almost as a circle anyway because the extrusion tends to round out sharp corners. There is a detailed write-up about this method, but I cannot find the URL at present, maybe someone else has it.

Dave