Possible bug with support blocker/cutting mesh?

[OnCor 0]

Hi all. I print two piece boxes for electronic components. The top piece has some openings in it for buttons/LEDs and lays top down on the build plate (which is textured to help hide the lines) during printing. The 3D printer I'm using can move fast, but doesn't doesn't do so well when it has to print small details like this. I wanted to decrease the speed when it is printing these features, so I attempted to use a support blocker and then change settings in the cutting mesh. For some reason Cura wants to put a wall around the perimeter of the blocker which isn't needed and sort of distrupts the flow of the print when it comes to that area. Is there a way to prevent those walls from being generated or might this be a bug? I'm currently using Cura 5.2.1. I tried using the "Small Feature Speed" option, but that ends up applying to other areas of the part which is not desirable. Any help here is greatly appreciated. Thanks!

Split Saturn Top.3mf

[GregValiant 1,261]

A support blocker when configured as a Cutting Mesh, Infill Mesh, or Normal Model is another mesh on the build plate.  It is going to have it's own boundaries and properties.  That's the normal behavior.  You can set the Modifier Mesh to not have any walls but that only affects itself.  Consequently, the hole that a Cutting Mesh might create in the main model is going to have walls around the hole because that's how the main model is set.

 

For that particular model, if you set the blocker on the inside floor then you will get (what I think) you are looking for.

This is in "Speed" view and the surfaces are not affected but with the block resting on the inside floor those small features will go down at the slower speed and your outside and inside "show" surfaces won't have the wall marks.

 

I always need to play with the modifiers for a bit to get what I want, but there are going to be the occasional compromise between what I want and what I can realistically get.

Edited September 24, 2023 by GregValiant

[OnCor 0]

Thanks for the information GregValiant. Unfortunately I also need the walls of the holes that cut through the top to be slowed as well because it seems they get misshapen by the faster speeds. The solution you proposed will help to some extent, but won't entirely fix my issue. I was hoping there was some other way to eliminate those walls around the support blocker. I'll keep playing with the settings to see what other ways I might address this issue. As you mentioned I might have to make some compromises here to get an acceptable result.

[GregValiant 1,261]

A side effect is that without the walls there is nowhere for Cura to stop and change settings.  If an extrusion starts at the exterior wall outside the block and travels into the block that will be at the starting speed.  The next extrusion might start inside the block and that would be at the adjusted speed.

The way you had it didn't look bad.  0.3 off the build surface allows the bottom skin to go down without those extra walls.

 

You could design a custom block.  It would have protrusions that drop into the holes and are 3 wall thicknesses bigger than the holes.  It's another workaround, but that often happens in these custom situations.  If you have to make a lot of them it would probably be worth the time.

[OnCor 0]

As it turns out I will probably end up printing outer walls fairly slow on this new printer to address VFAs caused by the belt system (it's Core XY), so that will address the issue of getting those holes printed correctly. If there ends up being a hardware fix that addresses that issue and I am able to print faster I may look into the workaround you suggested. It does seem like it could be a better approach than trying to slow down that entire section of the piece. Thanks again!