Cura's Handling of Wall and Nozzle thicknesses

[illuminarti 18]

Inspired by a conversation over on the Google Group, I finally wrote up the results of some testing that I've done on the interplay between wall thickness and nozzle width settings in the current (Skeinforge-powered) version of Cura.

Basically, if the wall thickness isn't an exact multiple of the nozzle width, some weird things are going to happen, because the extrusion rate and the spacing of the extrusion paths will no longer agree. Depending on the settings, this could lead to under- or over-extrusion.

One place you might see this is when using Cura's 'Fast' quickprint mode, because it has a 0.56mm wall width, and a 0.4mm nozzle width.

The best way to avoid this is to make sure that you use wall widths that are an exact multiple of the nozzle size (e.g., 0.4mm, 0.8mm, 1.2mm etc, for a standard 0.4mm nozzle). And encourage Daid to get us the new improved 'Steam Engine' backend for Cura ASAP!!

There's more about this issue on my blog:

http://www.extrudable.me/2013/04/08/walls-and-nozzles-and-cura-oh-my-or-quickprint-is-broken/

 

[ian 32]

can i ask ?

last night I designed a tablet box for my girlfriend, it had thin 2mm seperating walls between the different table sectors.

I of course as proud Cura user, gcoded it up and printed it.

The results were very good with clean walls and very accuarte but the seperate walls had nearlly no bonding between the two sides of a wall.

My question is, is this a big problem for all Cura users ?

Is this on the TO DO list for future Cura upgrades ?

Would adjusting the the nozzle size in cura upwards solve this problem ?

Thanks and best wishes.

Ian :smile:

 

[Daid 306]

RepetierHost does a horrible job at showing extrusion widths. I'm not sure what it's doing, but it doesn't use the proper values from each segment. I noticed this because I had a bug in my new engine which caused some segments which huge amount of extrusion. Which you could see in Cura's GCode view, but not in RepetierHost. So be careful when you use Repetier.

Other then that, you are right, it's easy to visualise with Cura. Use the default settings, only set the wall-thickness to 0.7, then you will see that the fills are under-extruded and have gaps.

Funny that nobody noticed before. But good catch! The fix is easy and I will have it out soon.

 

[edis 0]

Yes, i had this issue loong time ago. I started investigating this and then changed my part design and left it..

Here is a example of part sliced with cura, there is a rib with wall thickness of 1mm. Result with cura:

Is this the same issue you are talking about? The actual printed part is exact as shown, there is a gap between wall sides.

When using other slicers, e.g. kisslicer, the preview shows clean and filled rib (without any gaps), but i can't confirm the actual printed result, since i use kisslicer very rarely.

 

[Daid 306]

No, that's a different issue, that's named the "thin wall", which is that empty parts between the first perimeter and other perimeters are not filled.

 

[ian 32]

is the thinwall issue going to be solved in cura soon ?

I really really love cura BIG FAN :-) but i hate how my thin details are getting smashes becasue of this issue.

Ian :-)

 

No, that's a different issue, that's named the "thin wall", which is that empty parts between the first perimeter and other perimeters are not filled.

 

[illuminarti 18]

Daid - I've generally had good results testing with Repetier, although I agree it could do better at dealing with over extrusion. You are right that it didn't give any warning in the way it displayed the over-extruded gcode. In testing in the past, it would create a blob under the layer when you over-extruded (not ideal but its something), but I didn't notice this in testing yesterday. Maybe it's a settings change - I'm not sure. Having to tell it the width-over-thickness in visualization preferences has always seemed slightly odd to me.

One particular thing that I do like though is that it will highlight segments of the rendered filament to match the selected row or rows of the gcode text. That would be really great to have in Cura (and the ability to search gcode).... just a thought :-)

And if it is a quick fix that can be fixed, then that's awesome. I'm sure that will help a bunch of folks have fewer problems. To be honest, I was kind of assuming it would just go away with the new slicer.

(And if you do put out a patched version, I recommend you think about slowing down the Fast settings a bit. I definitely think, based on my tests, that it's trying to print faster than the nozzle can sustain ).

Finally, keep up the good work with Cura! It *is* great software, and the recent (and future) changes are exciting!!

 

RepetierHost does a horrible job at showing extrusion widths. I'm not sure what it's doing, but it doesn't use the proper values from each segment. I noticed this because I had a bug in my new engine which caused some segments which huge amount of extrusion. Which you could see in Cura's GCode view, but not in RepetierHost. So be careful when you use Repetier.

Other then that, you are right, it's easy to visualise with Cura. Use the default settings, only set the wall-thickness to 0.7, then you will see that the fills are under-extruded and have gaps.

Funny that nobody noticed before. But good catch! The fix is easy and I will have it out soon.

 

[lars86 42]

Hey Daid, any updates on this?

Thanks!

 

[Daid 306]

Yes, the fix is out and ready to download from software.ultimaker.com as 13.04, it doesn't have a lot of changes, mostly bugfixes.

This also tweaks the default profiles a bit, removing the extrusion problem that was noticed on the fast profile, and reflecting better what the Ultimaker can do.