Printing PETG Issues, Layers Above supports Not Inline

[laziraven 0]

I have been trying tune my PETG Profile and almost able to get a decent print out. But still having issues. The biggest issue I have is the few layers above my supports are not aligning. They are shifting inward when they should be straight. It seems that it's doing this at the same height as the flanged surfaces and maybe something to do with cooling? Some of the wall on the inner edges are also coming loose and the infill is not touching them for some reason. Maybe it's cause my Infill overlap % is too low it was at 20%.  I'm thinking maybe its not completely dry either and the fact that I don't have a bowden tube - My filament dryer only goes up to 55 Celcius so I compensate by leaving the filament in for 24 hours. But I still don't know if these are what is causing the issues. I have exhausted my knowledge of this issue. Please help. Im using a Snapmaker 2.0 and my filament is Overture. My print profile below.  I also have images of first layer over supports.

 

 

Edited April 27, 2023 by laziraven

[GregValiant 1,410]

Load the model into Cura.  Set Cura up with your normal settings for PETG (the ones you've been hoping would work).  Then use the "File | Save Project" command.  Post the resulting 3mf file here.  It will have your printer, Cura settings, and the model in it.

I have some left over PETG here and I don't mind using it up on a test print.

[laziraven 0]

S2A_LED_RING_10_overture_PETG.3mf Thanks. 

[GregValiant 1,410]

Those little tangs suck.  They have such a small contact patch to the build surface they could break away and scrap the print.  I decided to go with small support blockers configured to "print as normal part" so they would have a greater chance to actually last through the print.

Second, at 260° I think you are way too hot.  I typically print PETG at 230.  I haven't seen any problems with layer adhesion and it isn't as soupy at the lower temp.  I think that should be your first consideration.

Constantly changing speeds causes fluctuations in the pressure within the nozzle.  It makes it hard to tune a print.  Enabling Coasting and Retract at Layer Change causes the same problem.  All taken together, it makes this print more difficult than it should be.

Here is my little plan for the tangs.  They have a much better chance of surviving and they aren't hard to slice off with a hobby knife.

 

 

There is a lot of support interface going down and then there is very small part features being printed on top of it.  I would use Search and Replace or manually add a lot of cooling for layer 24 and 25 and then shut it off again at layer 27.  I have noted that when the interface is cool then the print doesn't stick as well.  Thinking about that I went so far as to add a pause before layer 26 and I gave it 15 seconds to cool.

 

Even with the crappy filament I used this print looks good.  Unfortunately, the part has such fine features that there is no way to separate it from the support without destroying the part itself.

 

What you have here is a part that needs a dual extruder printer so you can put down break-away or (even better) water soluble support.

 

 

[laziraven 0]

@GregValiant Hi Greg. Those are good points. I haven't had luck with lower temps that's why I tried 260, but you do bring up valid points. Ill pop one on with those changes over the weekend and see what happens. Thanks for the help!

[laziraven 0]

@GregValiant Hi Greg. Do you know of any way to target cooling for specific layers in Cura like you were saying? Doesn't seem to be a way to do that.

[GregValiant 1,410]

Funny you should ask.  I've started scribbling some post processors.

Unzip the attached folder and put "AddCoolingProfile.py" in the ".C:\...\UltiMaker Cura 5.3.1\share\cura\plugins\PostProcessingPlugin\scripts" folder.  It will be available like any other post processor under: "Extensions/Post Processsing/Modify Gcode "and then "add a script".

You can set cooling "By Layer" or "By Feature".  If I do say so myself (and I do) it's the Ritz.

 

 

AddCoolingProfile.zip

Edited April 29, 2023 by GregValiant

[laziraven 0]

@GregValiant thanks for the script!  So I printed with those changes you said. And the layers are still not sticking. I also printed at 230 temp. With 20mm/s general speed, with those adjusted retraction settings and coasting off. Did I miss something? Here's my cooling settings:

 

 

 

 

 

Here's the print:

 

The bottom on support side look pretty good. But another problem that I can't seem to fix is this weird stringing and dislodging of the side walls in the inner corners... Have no idea why it's doing that. I've adjusted the travel speeds slower in past but it didn't seem to work. I'm now thinking maybe it still has something to do with the support interface layers being to cool?

[GregValiant 1,410]

I don't think "too cool" is coming into it.  The print I did came out very well.  My problem with it is that I can't divorce the support from the model.  The cross sections of the model are so thin that trying to muscle the support off is wrecking the print.  Those little spring tabs fail really easily.  There is a lot more support than there is model and the support is more robust.  

 

The extrusions that are cutting across the radius instead of staying in place concern me.  They should be following the radius.  I've seen that when printing "outside walls first" but it shouldn't happen with the single wall support structure.  Part of that could be a printer issue.  What do you have for a hot end on the printer?  (Is it the stock unit or did you swap it out for something different).

 

Have you tried printing that piece in PLA?  I understand that PETG is your material of choice but PLA is easier to deal with and a PLA test print might give you a better handle on how to approach this with the PETG.  There is no doubt that you have a tough piece to print.  A PLA test print will also give you an idea of what I'm talking about in regards to the support removal.  I've got all kinds to tools for that and I still scrapped the print.

 

You could try switching the Cooling Profile over to "By Feature" and just running the fan on the Support-Interface and off on everything else.  

 

 

Edited April 30, 2023 by GregValiant

[laziraven 0]

I didn't have too much problem removing the supports and was able to remove them without damaging the tang clips. The Hotend is stock to Snapmaker 2.0. I actually did print PLA I totally forgot. I did an old part. Much cleaner but it did have the same problem with the layers above the support shifting in..  so it may be something else and not my settings. I've updated my cura also so dont think thats the problem. I suppose I can try that...

 

[GregValiant 1,410]

I don't know anything about your printer, but I was starting to lean towards maybe a mechanical problem.  It certainly doesn't seem to like printing PETG very much.

[laziraven 0]

Yeah. I've also just updated the firmware. And I reprinted the part and it kind of printed worse. I'm just going to contact Snapmaker. Thanks for all the help though. You are a wizard 🤘

[PartySausage 24]

On 4/29/2023 at 8:33 PM, GregValiant said:

Funny you should ask.  I've started scribbling some post processors.

Unzip the attached folder and put "AddCoolingProfile.py" in the ".C:\...\UltiMaker Cura 5.3.1\share\cura\plugins\PostProcessingPlugin\scripts" folder.  It will be available like any other post processor under: "Extensions/Post Processsing/Modify Gcode "and then "add a script".

You can set cooling "By Layer" or "By Feature".  If I do say so myself (and I do) it's the Ritz.

 

 

AddCoolingProfile.zip 7.53 kB · 2 downloads

I'm checking out this processor as I'm trying to sort out the crappy stringy layers i get above my supports when printing petg without the support sticking to the print & was wondering if when using by feature you can restrict the settings to specific features only say support interface & leave the other settings as per profile? 

[GregValiant 1,410]

"Advanced Cooling Fan Control" is now included with Cura.  You can just pick it from the post-processor list.

 

It can be configured in a couple of different ways.  You can have more than one instance of the script running, and you can adjust the fan within layer ranges.

For example, you can start making "By Feature" adjustments at layer 10 and ending at layer 15 with "Support-Interface" fan speeds at 100% and all others at 0.  Then set the "Final Fan Speed" to 0 and the fan would shut off at layer 15.

A second instance could start at layer 35 and then turn off the fan at layer 40.

"By Feature" works well for larger prints.  On small or fast prints, the "spin up" and "slow down" times of the fan come into play.  You end up with more of an average speed than exact speeds.  With some practice you will see when "By Layer" is a better choice even through "By Feature" may be tempting.

 

That's just an example but real-world you would just start at Layer 1 to Layer -1 (the whole file) with the support-interface at 100% and everything else at 0%.

There isn't an indicator in a Cura gcode for "first layer over support" so I could only use the "Top/Bottom" fan settings for the "Skins".  You can set the "Skins" fan in specific layers and that would cover the "first layer over support" (and over infill).

 

 

 

 

[PartySausage 24]

Thanks @GregValiant I'd spotted that it had been added to Cura builds & had a little play earlier using layer numbers setting the fan to 100% for the layers through the interface to the bottom surface, which although made a small improvement in the overhang surface above the support it wasn't a huge leap in quality & the outer wall had some imperfections where the cooling was maybe too much for that feature so I'll try a test using the features mode specifying start & end layers to see if that yields better results.

I also did test with the Supported Skin Fan Speed in the Cura Supports settings, which didn't improve things much either. Although with the test prints I did with that setting & also the test prints I did with the post processor I was able to reduce the Support Z distance a little & it was still fairly easy to remove the supports.