PETG PRINTS BRITTLE, NO MATTER WHAT I DO?  

RE: PETG PRINTS BRITTLE, NO MATTER WHAT I DO?

Update 3.  Printing with a brand new spool of PETG.  I have started to slow the print speed with the control knob after the print starts.  This appears to be helping.  I tried 75% speed, and that did seem to help (print didn't break as fast, but still broke).  Then the next print - I slowed it to 50% and kept the cooling fan speed at about half (when cooling at 65, I set to 40, when cooling at 125, I set to 65).  This helped even more (print did not break as in image above.).  

This further reinforces that somewhere along the way (perhaps) Prusa increased print speeds and or cooling to account for something in their environment or their testing - where in my environment - the previous settings created good results.  Now with current default settings - the prints are brittle with poor layer adhesion.  

Will try to print more tests tomorrow.

RE:

I think you are doing all the necessary trial & error things. I print extensively with PETG and have used Eryone, Polymaker, Overture.. but I don't use Prusament because it is 3x the cost here. I seldom use more than 30% fan (usually about 220-230C).. I only use higher fan if I have bridges that I need cooled fast. I read that some use zero fan. So you should be able to try from 0-30% fan while also varying the temp. But realize that your strength (or lack of it) is coming mostly from layer line adhesion rather than strength of the PETG itself, and so orientation will have a major effect in strength. No matter how well you dial it in, a cylinder printed flat will be stronger (from a sheer force perspective) than one printed vertically in an FDM process. However, they are often more than 'strong enough'. But I continually have models break (usually axles, pegs or legs) along layer lines that are printed vertically once any unforseen extra force gets applied (usually clumsiness in handling).. 🙂

RE: PETG PRINTS BRITTLE, NO MATTER WHAT I DO?

crab - I agree with everything you are saying about how FDM prints work 👍 Thank You.

Have you experienced what we are experiencing? 

I have Electric skateboards that I have made with 3D printed PETG.  The "Gears" the "Battery Boxes"...  My big board has some 800 miles on it with the same 3D printed Gears (printed over 5 years ago)...  Never had a problem...  So what I am experiencing now - Is new to me...  Something has changed - Perhaps the fan speed...  But why all of a sudden would I need less fan now - when previously stock generic settings worked great...? 

I will try less fan today with the slower speeds and see if I can get relatively strong parts again...  Thank You

RE: PETG PRINTS BRITTLE, NO MATTER WHAT I DO?

No question.. it is weird.. turn fan right off.. then print at 235C.. see what happens.. sometimes things change without realizing it.. sometimes it is environment temperature or drafts.. I once tried to correct stringing on all my filaments.. drove me nuts for about a month.. come to find out my nozzle was worn down too far and I was getting too much extrusion.. took a while to find that out.. new nozzle.. new printer..

RE: PETG PRINTS BRITTLE, NO MATTER WHAT I DO?

You should lay your prints on the side for increased strength. You will always loose a LOT of strength when you came which way the layers are laid.

RE: PETG PRINTS BRITTLE, NO MATTER WHAT I DO?

Thank you all for your comments and suggestions and to help clarify -

This post is about A change to inter-layer adhesion.  In the past - layer adhesion good... Now... Not so good.  (This post is not about how to print strong parts, but why the part is not as strong as it was in the past when printed.)  Thank you so much for all the great suggestions.

Update for this weeks Tests. 

I have slowed my prints to 50% with the control knob on the front of the printer.  I also, in the slicer changed the Cooling Fan to

Min=0% and Max=30%

And as mentioned before - brand new PETG filament.  

So - it looks like I have things working nicely now (I believe)... I am thinking that my layer adhesion is back to normal. 

I currently believe the change that has caused the issue is firmware and or slicer updates that have sped up the printing...  

Another good result is my PLA quality has also improved where now I have ZERO stringing on my PLA parts ( reduced print speed to 50%).

The grey PETG prints seem to be strong with good layer adhesion.  And the marble PLA figure has zero stringing. 

RE: PETG PRINTS BRITTLE, NO MATTER WHAT I DO?

Is it possible that your part cooling fan is working too well? Try printing with the fan set lower (or off) and see if that fixes the problem. (Have you changed fans between the prints that were strong and those that have poor layer adhesion?)