Diagnose this PETG problem

Ask the MakerGear community for assistance...
Post Reply
alackofcolor
Posts: 10
Joined: Mon Apr 04, 2016 11:13 pm

Diagnose this PETG problem

Post by alackofcolor » Tue May 16, 2017 4:48 am

I've read other posts on the forum about printing PETG and have adopted most of those print settings, but I'm still experiencing some issues. The outside of this piece looks pretty nice, but the inside surface, where all of the layer changes occur looks pretty bad (see attached picture). It has blobs, strings, and burnt bits all over. Here are some pertinent print settings:

Hatchbox PETG
240 extrusion temp
50 bed temp
0.88 extrusion multiplier (I use 0.89 for PLA)
2 mm retraction
5 mm coast
45 mm/s print speed

Any idea what could be causing what is in the picture?
Attachments
FullSizeRender.jpg

User avatar
ednisley
Posts: 1089
Joined: Fri Apr 11, 2014 5:34 pm
Location: Halfway up the Hudson
Contact:

Re: Diagnose this PETG problem

Post by ednisley » Tue May 16, 2017 1:38 pm

alackofcolor wrote:0.88 extrusion multiplier (I use 0.89 for PLA)
The actual value of the multiplier isn't important, it's whether the extruder produces the correct thread width: if you haven't printed and measured a thinwall calibration square to set the multipler, do so. The correct value ensures you're not overstuffing the part and should reduce the dreaded PETG hair problem.

After you have a calibrated extruder, then reducing the setting slightly will starve the extrusion and may further reduce PETG hair. However, the top and bottom surface fill may suffer, so proceed carefully.
the inside surface, where all of the layer changes occur
It looks like many of the perimeter threads pulled loose from the infill on those protruding features, which happens more on concave surfaces like the inside of that sheet. Print the infill pattern first, then the perimeter threads, so they have something to hang onto.

Turn on "Avoid crossing perimeters" to keep the nozzle inside the part. However, that may cause problems with PETG, because skimming the nozzle over the already-printed interior may collect too much gunk on the nozzle.

Also, preview the G-Code to verify the model doesn't have any problems that produce weird paths. I doubt that's the case, but it's always good practice when you see random threads hanging all over the place: the nozzle may be putting plastic in mid-air because the slicer had trouble parsing the model.

alackofcolor
Posts: 10
Joined: Mon Apr 04, 2016 11:13 pm

Re: Diagnose this PETG problem

Post by alackofcolor » Tue May 16, 2017 2:06 pm

It looks like many of the perimeter threads pulled loose from the infill on those protruding features, which happens more on concave surfaces like the inside of that sheet. Print the infill pattern first, then the perimeter threads, so they have something to hang onto.
Yeah, there are a bunch of threads that aren't catching on the protruding features on the underside, like you've mentioned. I've seen that on PLA prints of similar shape as well, but it's especially bad here. When you say print the infill pattern first, and then the perimeter threads, are you saying to use the Outline Direction: Inside-Out in Simplify3D? I'm doing that already. But if you mean something in addition to that, I'm not sure where that setting is. Thanks for your help.

User avatar
ednisley
Posts: 1089
Joined: Fri Apr 11, 2014 5:34 pm
Location: Halfway up the Hudson
Contact:

Re: Diagnose this PETG problem

Post by ednisley » Tue May 16, 2017 7:35 pm

alackofcolor wrote:Inside-Out in Simplify3D? I'm doing that already.
I use Slic3r, so I don't know what S3D calls things.

Slic3r has two settings:
  • "infill_first" does exactly what you think it should
  • "external_perimeters_first" lays down the outer perimeter first, then works inward
I have the first options set and the second cleared: each layer starts with the infill and ends with the outermost perimeter thread.
aren't catching on the protruding features
If those features aren't faired into the surface and have too much overhang (particularly on the concave side), then building them from the inside out won't help: without supporting threads underneath, the threads will fall loose. Perhaps tweaking your model so the bottom of the projections extend at 45° will improve the results.

You should also force the slicer to put all the layer starts in a column, so it doesn't (try to) start a thread in the middle of an overhang.

Post Reply