Hugly perimeters and brittle parts of piece  

Re: Hugly perimeters and brittle parts of piece

210°C hotend temperature seems to be fairly low for PETG.
personally I print my PETG @ 240 - 255°C.

furthermore I recommend to set the seam position to "aligned", not to near or fastest.

beside the tall pillar, the top end with the treads and the bottom with the base looks fairly good.

Re: Hugly perimeters and brittle parts of piece

Thanks for your reply. I know temperature sounds low for PETG but on the extrudr.eu website they say 205°C as recommended temp. I didn't remember but I think I saw another brand of PETG with such low temp. https://extrudr.eu/collections/petg/products/extrudr-mf-petg-black

I have seen this "aligned" parameter and that make sens for cleaner perimeters. Do you think it can also solved the fact that the external perimeter is done much faster than the infill?

Re: Hugly perimeters and brittle parts of piece

FormFutura HDGlass is also very low in temp for a PETG (195-225°C) : https://www.formfutura.com/shop/product/hdglass-blinded-black-226?category=164

Re: Hugly perimeters and brittle parts of piece

I think you really need to slow down the print on the small parameter parts.

Think of it this way, there is not time for plastic to cool properly when the nozzle is back on it again printing hot stuff onto gooey stuff. That is why your small pillar looks bad, but the larger (more time to cool) base looks fine.

For Slic3r, under Filament -> Cooling -> Cooling thresholds there are two parameters "Slow down if layer print time is below" and "Min Print speed."

These should help.

See also:

http://shop.prusa3d.com/forum/print-tips-slic3r-settings-kisslicer-model-repair--f12/trouble-printing-m10-bolt-thread-t5710.html

Re: Hugly perimeters and brittle parts of piece

Hi All,

Sorry for late answer and thank you for your help 😉 . I could finally print correctly this piece playing with the "Slow down if layer print time is below" and "Min Print speed" parameters. I set "Min Print Speed" to 5mm/s and "Slow down if layer print time is below" to 35 seconds.

However, I had to slow down the external parameters in the Print settings -> Speed -> Speed for print moves menu. After experimenting several similar cases, those two parameters doesn't affect the external perimeter speed (it is going faster when printing the external perimeters than internal perimeters or infill). Have you ever heard about this issue?

Re: Hugly perimeters and brittle parts of piece

> However, I had to slow down the external parameters in the Print settings -> Speed -> Speed for print moves menu. After experimenting several similar cases, those two parameters doesn't affect the external perimeter speed (it is going faster when printing the external perimeters than internal perimeters or infill). Have you ever heard about this issue?

Frankly I don't quite understand what you mean. Do you think there is an issue with how Slic3r handles the printing speeds? If it is the case, would you please create an issue into the issue tracker and describe as much detail as possible, so I can reproduce your problem?

https://github.com/prusa3d/slic3r/issues

Thanks, Vojtech

Re: Hugly perimeters and brittle parts of piece

Thank you for your reply and sorry to ne be clear enough. I finally found someone that raised the issue I have tried to describe on alexrj/slic3r repo. It is better described and done deliberately :
https://github.com/alexrj/Slic3r/issues/4070

Re: Hugly perimeters and brittle parts of piece

In my experience, PETG has been really brittle (bad layer adhesion) unless I disable the fan for the print.

Re: Hugly perimeters and brittle parts of piece

> 0.3mm layer height (based on 0.35 profile)

What nozzle do you use? 0.4mm diameter?
0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

> 210°C hotend, 80°C bed
Likely too low for PETG.

> Infill pattern: cubic at 20%
You may try to switch to a grid infill. The cubic infill may lay down multiple strands of filament one over the other along the inner perimeters, which for a tiny or narrow infill may cause the infill to bulge the perimeters outside, making the infill pattern visible. This will be fixed in Slic3r one day.

Actually your issue may really be caused by a too low extruder temperature for PETG. With a too low extrusion temperature, the viscosity of the extrudate is too high, requiring an excessive nozzle pressure for a continuous extrusion. In that case the rapid changes of extrusion rate due to the cooling slow down on internal perimeters versus not slowing down on the external perimeters may cause the print defects you are experiencing. Also it seems to me that your layer adhesion is low, indicating a low nozzle temperature.

Re: Hugly perimeters and brittle parts of piece

Excuse me if it was already asked:

Did slic3r report any errors on the Object? I think it can get confused by wrong normals on the mesh and then print outside as inside which might explain the reverse in Perimeter speeds.

Carsten

Re: Hugly perimeters and brittle parts of piece

0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

Some of us have been saying for years that this profile shouldn't be used. If you are agreeing, why is it still included?

Re: Hugly perimeters and brittle parts of piece

> 0.3mm layer height (based on 0.35 profile)

What nozzle do you use? 0.4mm diameter?
0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

> 210°C hotend, 80°C bed
Likely too low for PETG.

> Infill pattern: cubic at 20%
You may try to switch to a grid infill. The cubic infill may lay down multiple strands of filament one over the other along the inner perimeters, which for a tiny or narrow infill may cause the infill to bulge the perimeters outside, making the infill pattern visible. This will be fixed in Slic3r one day.

Actually your issue may really be caused by a too low extruder temperature for PETG. With a too low extrusion temperature, the viscosity of the extrudate is too high, requiring an excessive nozzle pressure for a continuous extrusion. In that case the rapid changes of extrusion rate due to the cooling slow down on internal perimeters versus not slowing down on the external perimeters may cause the print defects you are experiencing. Also it seems to me that your layer adhesion is low, indicating a low nozzle temperature.

Sorry for late answer but I took the time to test few parameters on several prints as well as tower test (for temp) and I have now switched to 225°C. Going higher seems to only add stringing. I have not used the 0.35 profile since your comment. My prints are clearly better and stronger. In conclusion, my main issues were printing too fast and with a too low temperature. Thanks again for the help 🙂

However, I am still not convinced by there explanation here : https://github.com/alexrj/Slic3r/issues/4070 (mentioned previously). I understand that a different speed might change the look of the external perimeters but that depends on the filament type. Plus, even if the color might change a bit that doesn't mean the print looks ugly, maybe even the opposite!

Excuse me if it was already asked:

Did slic3r report any errors on the Object? I think it can get confused by wrong normals on the mesh and then print outside as inside which might explain the reverse in Perimeter speeds.

Carsten

The difference in speed is due to that : https://github.com/alexrj/Slic3r/issues/4070

0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

Some of us have been saying for years that this profile shouldn't be used. If you are agreeing, why is it still included?

I agree with this, or at least we should have a warning somewhere in the profile (title?) that this one is kind of hack