[ADDED] Infill Line Thickness

[BaronWilliams]

One of the things that can make infill much stronger is to have infill walls that are more than 1 line thick.

A single wall of extruded filament is much more likely to collapse than a double or triple wall. We all know that 3 thin separate 1 shell walls are not as strong as a single 3 shell wall. A 3 shell wall is much less likely to buckle. This is why highways don't use a series of thin walls to support an overpass. They use a few very thick walls instead.

Unfortunately most slicers don't let you adjust the number of extruded filament lines used to make walls in the infill, and simply use 1 line of extruded filament for all walls. Most slicers let you adjust the percent of infill, where higher infill percentages give stronger infill, but the added strength from increasing the infill percentage relies on different principles and is not always an ideal way to increase infill strength.

Imagine using tooth picks to construct walls to hold a brick. You have 1000 tooth picks and Elmer's glue to make your support (the glue is just used the join the toothpicks together, large blobs of glue are not allowed). Toothpicks must be laid on their side horizontally. Walls can only be 1 toothpick long and not connected to other walls. Walls can be 1 or more toothpicks thick. All walls must be 100 toothpicks high and parallel to each other with no cross sections. You must use 1000 toothpicks to construct your walls. If you choose to make 10 walls that are 100 toothpicks high and 1 toothpick thick, you're brick is going to collapse because the toothpick walls that are only 1 toothpick thick are going to buckle as soon as you put the brick on them. There's nothing preventing this because all the walls are parallel. If you instead make 2 walls, that are 100 toothpicks high and 5 toothpicks thick, the walls will not buckle.

In that toothpick example, in both cases the same amount of toothpicks are used. But the second method produces far superior results and is able to support the brick. The first method is not able to support the brick. This same kind of thing applies to 3D print. Instead of toothpicks we are using lines of plastic. Instead of glue we are using melted outer surfaces to stick the walls together. Other than that the two are quite similar.

How you construct infill is really quite important to strength, especially when using a low infill rate. Different objects may need different types of infill for optimal strength.

Infill that's 10%, but using walls that are 2 lines thick is stronger than infill that is 10% but using only 1 line thick walls. But it's a bit more complex than that because infill that is 10% using walls that are 2 lines thick has larger gaps between the infill lines than the same infill made of 1 line thick walls. This introduces weak support areas in the object the infill is supporting. For some prints with thin top and bottom layers this can be a problem. But for other prints with thick top and bottom layers this can improve strength a lot without having to increase infill percentage.


There is no 1 support structure that's best for all cases.

I would love to see the ability to add wall thickness to the infill so that this toothpick example case could be done properly in Simplify3D. Currently we only have the option to increase infill percentage, but not infill wall thickness, so we are forced to use the wrong solution for the toothpick example above.

I propose adding infill line wall thickness as follows.

For example, on the "Infill" tab we would have "Infill Line Thickness" where we specify the number of lines that make an infill wall. A value ranging from 1 to 99999 lines would be valid. If set to "1" line, the behavior is no different than it is now. If set to "2", then all infill walls are 2 lines thick. If set to "3", then all infill walls are 3 lines thick, etc. The infill percentage would still work the same. If using 10% infill, and an "Infill Line Thickness" of "1", then infill lines would be made using 1 line thick walls separated by 9 lines of space. If an "Infill Line Thickness" of "2" was used then infill lines would be made using 2 line thick walls separated by 18 lines of space. In either case it would still amount to 10% infill. Only the gaps and wall thickness would change.

With just that simple little addition, we would gain a lot more control in how sturdy our infill walls are. There have been many times where I needed super tough objects, with infill that's 10 walls thick, but the infill could be sparse because the top and bottom layers are also very thick. With most slicers, there's no good solution for this, because they slice all infill walls using only 1 line.


EDIT: The main failures we are fighting by increasing wall thickness in infill is failure from buckling, failure from weak walls, and failure from weak bonds. The thicker a wall, the less it is prone to buckling, the larger the bond area, and the stronger the wall.

Some might wonder how the bond area is increased. Let's look at 2 different infill walls. The 1st is 1 line thick. The 2nd is 2 lines thick. To give an equal amount of filament, we can make 2 walls that are 1 wall thick for every wall that's 2 lines thick. So the 1st wall example will have 2 walls, and the 2nd wall example will just have 1 wall. Both use the same exact amount of filament.

The 1st example is 2 walls that are each printed 1 line thick. For each wall, per layer, there can be as much as 2 bonds: a bond to the lower layer, and a bond to the upper layer. The top and bottom layers can only have 1 bond. That allows the 2 walls a maximum bond potential of 4 bonds per layer, but only 2 for the bottom and top layers.

The 2nd example is 1 wall that is printed with the same amount of filament by making the wall 2 lines thick. For this example, there can be as much as 5 bonds per layer: 2 bonds to the lower layer, 2 bonds to the upper layer, and 1 bond between the 2 lines making up the 2 line thick wall. The top and bottom layers can only have 3 bonds. That allows the 2 wall thick single wall a maximum bond potential of 5 bonds per layer, but only 3 for the bottom and top layers.

Both the 1st and 2nd example use the exact same amount of filament. They also take exactly the same amount of time to print. However, the 2nd example has more bonds per extruded line. In the 1st example, per extruded line, there's a maximum of 2 bonds (above and below). In the 2nd example, per extruded line, there's a maximum of 3 bonds (above, below, and side to side). 3 bonds are stronger than 2.

So not only does the double lined wall have less of a potential to buckle because of it's thickness, it's also making better use of the hot end by fusing more filament together, while taking no additional power, no additional time, and no additional filament. We all know that more bonds = better strength.

[laird]

That all makes sense, but at the same time we don't want support to be too strong, or it'll be difficult to remove.

Rather than making support multiple filament lines thick, how about making support a grid of 1 filament wide walls? That's strong structurally, but still easy to crush when removing support. Conveniently, S3D can generate this now, if you put in two infill angles (e.g. +45 degrees and -45 degrees, or 0 and 90 degrees). The result is support where each layer is at right angles to the previous layer, so it forms a grid that's fairly strong, but it's still easy to remove.

[66tbird]

That all makes sense, but at the same time we don't want support to be too strong, or it'll be difficult to remove.

Rather than making support multiple filament lines thick, how about making support a grid of 1 filament wide walls? That's strong structurally, but still easy to crush when removing support. Conveniently, S3D can generate this now, if you put in two infill angles (e.g. +45 degrees and -45 degrees, or 0 and 90 degrees). The result is support where each layer is at right angles to the previous layer, so it forms a grid that's fairly strong, but it's still easy to remove.

Infill and support are two different things.

I'm all for double line infill at times. Good feature request.

[dennisjm]

+1

[kevin]

+1
I am using 0.3mm nozzle. Infill line width is 0.36 default, so thin that it will not be as strong as if able to set to 0.5-0.6mm.
If manual set line width to 0.5mm, the perimeter will be affected resulting a larger print size and smaller internal holes.
Ability yo set infill line width will helps "print sparse infill" every 2 layers better especially for smaller nozzle size.
Lesser larger infill lines VS Many Smaller infill lines with same infill % will definitely SPEEDUP PRINT TIME.

[S3D-Jason]

This feature was implemented in version 2.2