Optimise Print Order

[Gerrardh 1]

Hi all,

 

I'm having issue with Cura's printing order. We have options to print 'outside to inside' or 'inside to outside' but neither option is useful. The problem is that 'outside to inside' means that any early defects with bed adhesion (usually the first few mm of a print line) will be visible in the outer skin. However, with 'inside to outside' you end up with the printer making several small extrusions that are intended to fill in very small gaps being printed first - and similarly, if these have any issues with bed adhesion, then they will partially or completely come off the bed. If they come off the bed, they stick to the nozzle only to be deposited somewhere else on the part later. Furthermore, material that sticks to the outer surface of the nozzle eventually bakes hard and causes more problems later (stringing, blobbing etc) - it's important to keep the outer surface of the nozzle clean.

Video showing what the opportunities for small defects when printing 'inside to outside': 

 

Is there a way in cura to change the print order so that:

A) we print away from the inner/outer wall boundary - that is, outer walls and skin print outwards, inner walls and infill (or skin on top/bottom layers) print inwards.

B) print 'outside to inside' but with the outer skin last?

C) Print first layer 'outside to inside', then subsequent layers 'inside to outside' - this is non-preferred, but it would only leave opportunity for one such defect

 

This problem is super frustrating, I've been fighting it for years hoping that Cura would change something.

 

Thanks in advance.

Edited September 5 by Gerrardh

[Slashee_the_Cow 410]

At present I'm computer deprived so I can't look exactly but you can try and get rid of the small bits by playing with the (IIRC on the names) Walls > Wall Filter Transition Angle and Walls > Wall Filter Transition Length settings.

If you can post a Cura project file (,3mf, get it set up then go to File > Save Project) for something you're having trouble with than someone else could look and try to find the best solution (or I could in a couple of days when I'm once again at a machine capable of running Cura).

[Gerrardh 1]

Hi there,

 

Thanks for the suggestion. I tried a few different settings below, exaggerated to highlight their effects.

It's easy enough to make those first few lines larger - potentially large enough to give them sufficient bed adhesion, but you can't make them small enough to dissappear.

 

I realise now why the bed adhesion is a problem with these small lines - The slicer is extruding less than the line width to create a thinner line - effectively stretching the extruded plastic. This requires more adhesion between the extruded plastic and the bed/part, which is not available at this early stage. 

 

I've also attached a copy of the project file for reference.

 

LeafSpring_x4.3mf

[Slashee_the_Cow 410]

10 hours ago, Gerrardh said:

realise now why the bed adhesion is a problem with these small lines - The slicer is extruding less than the line width to create a thinner line - effectively stretching the extruded plastic.

That's not really how it works. How much is extruded is based on a volumetric calculation - basically line width x layer height x flow rate. The filament doesn't have a "native" line width or anything so it's not stretching it, the reason it has trouble adhering is just that there's less surface area (which is why it's common to set it to do the first layer at 150% line width).

 

I'll have a look at your file to see if I can find the perfect combination of settings or something when I'm not several hundred kilometres away from my computer (to anyone who knows where I live: don't try to rob my house, there isn't anything worth having and there's someone still there anyways) so hopefully tomorrow night.

(FWIW I'm using a Chromebook, and while Cura isn't supported at Chromebooks people are always using it anyways, I'm offering a cash bounty to anyone who can get Cura 5.8 running on mine.)