Fill density with cura & small objects

I’m having a problem trying to print a small lego block 1 x 6 from this source: … -framework

When I print that brick with 0 density it’s all fine and they turn out mostly perfect. But when I raise the fill density the small inner cylinders(3,5mm) inside the brick get filled with too much filament and so they grow too fast until the they get ripped off from the print head. I tried different densities and the problem always occurs when one of these inner fill lines happen to be inside one cylinder.

So is this a known issue with small objects and CuraEngine?
“Slic3r” is until now no alternative cause I can’t figure it out how to get all these settings right.

Can you get different fill densities in one printing object?

Can you post a picture of the problem?

This is the same model only difference is the fill density.
The problem occurs at fill rates of 5 - 100%. Only one of the inner fill lines needs to be inside of one cylinder to mess it up.

Fill Density 0%

Fill Density 100%

Is the thermistor properly seated in the heater block?
It looks like it maybe running a little hot.

Can you post a link to the STL file? I will try some tests here.

See the link in the first post, its the lego block 1 x 6 from that zip file.

@Wrong Way
I don’t think it’s a thermistor problem cause all other prints turn out pretty much perfect.

I have to correct my conclusions there is also a problem with 0 fill density. When the block is build up higher layers sometimes some of these small cylinders get too much filament while the other ones are perfectly fine.

So maybe a firmware bug?

Just an assumption, did you set the nozzle size correctly in cura?
Did you set a good average of the MEASURED filament diameter?

I didn’t change anything in Cura. Did I miss something in the manual?

I can’t even find that “nozzle size” in cura settings… only in the Printer settings in Repetier-Host and there it seems to be OK -> 0,35mm.

MEASURED filament diameter:
How do you do that? I mean I can only take a measure on some of the outer spool layers. It’s velleman original filament.
I measured at some points between 1,75 to 1,73 mm, but its a cheap digital caliper I wouldn’t trust 100%.

Do you use repetier with cura engine or the standalone Cura Software?

In repetier you will find the filament diameter on the filament tab and the
nozzle size on the extrusion tab of the cura engine settings.

The standard Vertex setup, Repetier-Host with Cura/Slic3r build in.

Then measure your filament diameter at let’s say 10 to 15 different points along a 30 mm piece and average the result.
Then set this as your filament diameter in cura settings.

Some filaments (especially most craper ones) have a great variation in diameter and almost none is spot on 3mm, or in your case 1.75mm.
If you average the difference you will get more consistent extrusion volumes, and thus more precise prints.

Thanks for these infos concerning the “measure your filament”’, I’ll keep that in mind.

But until VEL327’s test on another Vertex hasn’t ruled out any software bug I’ll stick to the default settings. Most parts I’ve printed so far turned out very well.

First I thought about it and wondered if this is maybe an typical bowden tube printer issue. Cause for these small cylinders to print the filament transport has to stop and to start again because these cylinders are separate from the hull of the lego brick. Maybe these separate small parts, when the printer needs to very accurate stop & forward the filament, are too difficult to handle cause the bowden system is not precise enough?

But the filament forwarding is interrupted all the time during any print which turn out pretty perfect, so that can’t be such a huge issue. And that can’t explain the huge differences in print quality with the fill density 0% and 100%.

So I guess there must be some software problem involved(Repetier-Host / Cura / Firmware).

Did you made any tests yet?


I am not in the office until 5 jan. But I will check asap when back.

Any updates on this issue?

Having the same problem here, using Cura directly.

I wondered if “Slic3r” would make the same troubles as Cura. But how can we compare the two slicers. Is there already a known good Slic3r setting for the Vertex that prints the same quality as the current Cura?

Somewhere on this forum I think read that Cura has problems in exactly calculating small circular/curved? objects because of the chosen calculating method? Probably this is related to this fill density problem?

I’m sorry I kinda lost track of the file after the holidays. I downloaded it again and will try a print.

Here it printed without a problem. Pictures are posted below. can you post your gcode?