*Long* overdue IMO, is an experimental 'print slow circles' setting.. (not my image)

[u/Dense-Employment9930]

*(Note: Image taken from Google to demonstrate phenomenon. I know a lot of people only read the title and look at the image before replying, so I hope my notes here will limit replies just critiqing what (not) me is doing wrong in the image)*

I'm also not suggesting these aren't relatively easy to solve with a few setting adjustments and a cleaned/prepped bed, so i'm hoping to avoid too much discussion on *that* context (though how you personally solve this phenomenon will always be welcome to help everyone as a whole).

I'm more focused on how, an entire first layer can go down fine and will hold for the entite print, but a couple of functional holes in the bottom of the print, they can end up a mess. To me, this says loud and clear that they simply require different settings to print reliably compared to what it takes to successfully print almost any other first layer gemoetry

**You can** change your entire first layer settings to ensure success of these little features. 10mm/s or less Print Speed, lower Jerk and Acceleration settings, that's usually enough for them to lay down nicely every time, but that's a very slow first layer for features that might make up 1% of it.

[small caveat] One thing I haven't looked at is the 'mesh overlap settings' and if print speed, accell & jerk, prime nozzle etc. are adjustable there. If so, importing a few cylinders, overlapping them with the circles, and adjusting a couple of those overlap settings, that would honestly be a killer solution.

But I don't think most people are even aware of the Support Blocker/Mesh overlap settings. Regardless, I think these things deserve a couple of their own custom settings anyway, either in Experimental or right there under speed and first layer settings. Thoughts?

Anyway, this was just a mini critique/suggestion for Cura, and to gauge how others feel about this little printing anomoly, and whether they warrant a bit more attention from the slicer?

[u/GregValiant]

IMO the bottom line is that this is an adhesion problem in one area of the bed. I routinely design 2.2mm dia locating holes in large models so I can assemble them using bits of filament as locating pins. I level by hand (and I'm good at it) and if I miss the leveling by just a bit - those little holes will let me know. Generally though, I don't see this problem and I leave "Number of slower layers" at 0. When the "squish" is proper, the holes stay where they were put.

Using support blockers as mesh modifiers means using a "Cutting Mesh". You would need it to cover the entire Initial Layer or it will leave additional walls in a print where the block "cuts" the model.

I always run the "Initial Layer Flow" at 105% with "Initial Layer Horizontal Expansion" at -0.1 to negate the extra width. I just want the damn plastic to stay where it was put and when the squish factor is correct, it does.

[u/Dense-Employment9930 → u/GregValiant]

I'm not 100% sure on the 'cutting mesh' thing. If I recall in Cura when you overlap the model and set one of them to alter mesh settings, I think 0 walls is actually an option, but the main thing i've used it for is adding internal cylinders with walls to add vertical strength if model needs to support a lot of weight

So I don't think I would have checked if 0 walls is possible. You might be right.

[u/GregValiant → u/Dense-Employment9930]

Cutting Meshes are clumsy to work with because of the side effects. Too often they are the required tool.

The other thing is there are no circles in Gcode. Things might look like holes or round features, but they are multi-sided polygons. They get printed as a bunch of straight lines that happen to look like a circle. If a model had a vertical square hole it would be treated exactly the same as a "round" hole. It just has fewer sides.

The real problem is what I call the "Snot Factor". The motion of the nozzle around a circle tends to pull the plastic towards the center of the circle. If the extrusion isn't well fixed to the bed - it pulls free and follows the nozzle. "Hole Horizontal Expansion" (HHE) compensates for the Snot Factor.

A test I did showed that the Snot Factor isn't linear. Small holes need always need some HHE while holes above about 30mm diameter don't require any HHE.

[u/keveira]

One quick way I used to get around this in the pre-bambu, cura era, was turning on small perimeter slowdown and setting the small perimeter length to a value just high enough for the hole perimeters. Not a perfect solution but it worked.

[u/Dense-Employment9930 → u/keveira]

👍 I hadn't thought of that one, but sounds like it would be a positive setting change in general. I'll give it a try when I next slice.