Same Cura setting with different quality

[Jake_Ding 0]

Hi guys,

I was always happy to play with PLA on the Anet A8 until recently I printed some small parts in bad shape. As you see in the pictures, the bigger part(70mm length x 70mm width) has good quality but the small part with the same Cura setting( listed below ) gets some cracks and uneven surface.

 

The major Cura settings are listed as follows: 1. layer height is 0.2mm; 2. wall thickness 0.8; 3. 100% infill density; 4. printing temperature is 220; 5. build plate temperature is 65; 6. printing speed is 30 and initial layer speed is 10; 7. regular fan speed is 70% and max is 90%. 

 

Could you help me find the reason why the smaller parts with the same Cura setting has bad quality? How to fix it? Thanks

 

Jake

 

 

 

[yellowshark 153]

Ok two things. Firstly; now this does differ between printers and filaments BUT  I think you are printing too hot. Using .200 layers at 30mm/s I would probably use 200 maybe 195. 220 is definitely too hot and is probably having an impact on your small piece. So take your temp. down as low as it will go, i.e. until you see under-extrusion and then push it up 5 and you should be fine.

 

The small piece. I suspect your layer print time with this is too short and so the printed layer is not cooling fully before the next layer is printed on top of it, so you get squelch. Having such a hot nozzle (220) will not help but I suspect lowering the nozzle temp will not fix this problem. In Cura, under the Cooling section, set your minimum layer time to 10 secs. and minimum speed to 10mm/s and tick the Lift Head option. When you print the the piece if the nozzle lifts then you know your layer print time is less than 10 secs. You now have 2 options. Just let it print like this but it may be better to extend the layer print time by printing a second or third copy of the piece.

 

Also you said your print speed is 30mm/s, that is good but make sure all your printing speeds are set to 30mm/s (excluding 1st layer).

Edited May 10, 2018 by yellowshark

[Jake_Ding 0]

Thanks, yellowshark!

 

The reason why I used 220 on the nozzle is because the lowest recommend temperature on that PLA spool is 210. I saw there are oozing/stringing inside of the small part, which means your suggestion is correct. 

 

I will lower the temperature to just above the under extrusion temp.  I will also try to print two parts at the same time. Other setting are adjusted as you recommended.

 

 

[yellowshark 153]

Good luck! Strange that the PLA is specified at a minimum temp of 210. I just checked the ColorFabb site and they recommend 195 and I have gone down to 190 without problem, that was probably.100/.150 layers at 30mm/s

[Jake_Ding 0]

Thanks for your comments! I will make a temp towel before I move on. 

[geert_2 558]

For colorFabb PLA I can even go down to 180°C if I print very slow on small pieces, 20mm/s, and with a thin layer height of 0.1mm. But usually 190...195°C and 25...30mm/s will do, on my UM2. Could be different for other brands and models.

 

So I second the view of yellowshark: lower the temperature, and print multiple parts together. But in my experience setting a "minimum layer time" does not give optimal results: if the nozzle stays above the model, it keeps radiating too much heat and prevents cooling. If the nozzle is moved away from the model, it tends to leak and cause artefacts. And the molten filament is sitting longer in the nozzle, thus gets more liquid and hotter: this is heat which also needs to dissipate. So, printing multiple models in one shot is better, or print a dummy block next to it.

 

For small models I often print a sort of "inverse" next to the real model. So that layer printing time, and thus layer cooling time, is identical for all layers. This gives best results.

 

Below are a few examples.

 

 

 

 

[Jake_Ding 0]

Awesome explanation! I love this forum! The better methods to print smaller parts are listed as follows based on yellowshark and geert_2's suggestions:

1 lower printing temp (both excessive high or low temp will let the part deformed);

2 less layer height, like 0.1mm is better than 0.2mm  (less material, less deformation);

3 slower printing speed (20~30mm/s except for the first layer);

4 print multiple parts or dummy parts (special designed to equalise cooling time) together to make sure the sufficient cooling time

[Berross 0]

A great forum and great members. A newbie says many thanks.

 

[yellowshark 153]

Hi @geert_2 I agree with you; I always always print two or more copies if the layer print time is too fast, for the reasons you describe. I suggested setting the layer print time to 10 secs just as an investigative step, although I did not make that clear, of course a stop watch is an easy alternative! Love your idea of inverse models?