I wanted to figure out a solution to help, but also because figuring out was intriguing to me and it will also probably help me one day.
When I looked at the models where I modified the infill, I noticed that the wall count of the infill mod has to be the same as the model’s wall count, if it is larger or smaller, there will be walls around it. In my cases, I only changed the infills, not the walls and infills like you are trying to do.
The solution I found will look a little strange in my Autodesk Fusion sketches, but works very well. Before I show it to you, I will show you a few of my earlier experiments for some suspense.
Here is almost the one, but I think the joining between the two infills is not strong enough
I used 10% gyroid infill in between the two to hold them together.
Here are a few close-ups at a few layer heights to show how well gyroid holds them together.
This method may look a little strange, but I tried the more intuitive methods first and you saw the sub-par results I got the first pictures I posted.
Here is how I did it in Autodesk Fusion
The different shades of red in the picture above are mods. The center mod for the gyroid infill to join the two honeycombs.The light red mod on the left for the smaller infill percentage, and the 1 line width (0.42) thick wall line mod on the left with the two pointed ends.
Here is the sketch
The 1.68 is 4 lines to represent the four outer walls to restrain the location of the pointed line. The pointed mod is 1 line thick, so that the model has 1.26 (3*0.42) of solid walls on the outside. Also notice that the pointed mod is within the 4 outer walls so it doesn’t add any extra walls. Since the main model has a wall count of 4 and the mod has a wall count of 3, it causes the main model to apply its 4 walls around it. In this case, the wall count could have been any number but 4, since the mod boundaries prevents it from having any more walls than 1. So since the mod was within the 4 line widths of the outer walls of the main model, the total walls on the thick part is 8.
If you want to get an extra uninterrupted solid wall on the outside of the model before it breaks into two parts, move the pointed line mod inside the interior box, instead of outside like it is now. Just note that doing this will make the left side walls a little thicker
Here are the print settings
Main Model
Wall Generator: Arachne
Wall Count: 4
Infill: 20% Honeycomb
Outer wall pointed Mod
Wall Count: 1-3 or 5+ (not 4)
Infill: NO CHANGE
Left Infill Mod
Wall Count: NO CHANGE
Infill: 10% Honeycomb
Center Gyroid “glue” Mod
Wall Count: NO CHANGE
Infill: 10% Gyroid
Arachne looks like it will be stronger at the wall transition than Classic. I was going to say that it would be better if the gyroid joining infill was a little further right, or the transition part was a little further left, so that the gyroid spans the weaker part when it transitions from 4 to 8 walls. But when I thought about it some more, it is best how it is, because the transition from 8 to 4 walls is more gradual. If the gyroid went over the 4 walls, there would be a sharp transition from the gryroid supported section and 4 walls, causing a stress point.
Arachne
Classic
