Second Layer print issues
Hi, I am currently having a print issue with PETG. I had this working at one point, but now can't seem to get my Prusa MK2S to print.
The problem is the second layer. The first layer lays down almost perfect looking. The second layer is very rough and material starts collecting on the head. I tried the default setting and even lowered the temperature to 235C first layer, 239 Second layer. I have adjusted the z-offset, but it doesn't seem to be lowering the print head any more. (Offset is currently around -.767).
The first layer, even though it goes down well and seems to have good adhesion, has separation between the strands, When I go to remove the layer, after the second layer fails, each strand comes up separately.
I have successfully printed PETG, (at least 2 Rolls), Carbon Fiber Nylon, PLA and several rolls of ABS. I haven't tried any other filament since the issue started with PETG. I did try re-calibrating the z-axis, but that didn't help.
Anybody ever seen this sort problem? Most of my issues in the past were related to first layer. Usually if I get past the first with a clean print, I have no further issues. Any ideas how to solve?
Re: Second Layer print issues
Here are some pictures to illustrate the problem. They are in reverse order, but the last one shows the first layer. You can see the gaps between strands. The middle one is the second layer. and the top one is after the print is removed from the print bed, again you can see that the first layer shows a very loose structure between strands.
I am using Slic3R, with .2 layer height, 60% infill. I have a 0.3 mm nozzle installed (This has been the case for a long time and has worked well). I am currently using a new roll of Hatchbox PETG Black. I previously tried Hatchbox PETG Blue, with the same result. I have printed this very same model on my CEL Robox and gotten perfect results, using the same roll of material.
Re: Second Layer print issues
Rewrote my post for clarity.
It is advised that PETG is printed away from bed for first layer due to its elasticity when molten. If this is the limiting factor, you should print hot (bed and nozzle) to max recommended for the filament brand. Slow is extra insurance, good advice for all filaments, nothing new there.
Now that we have the constraint of PETG first layer, we have to correct to improve quality.
I print in all manner of PETG blends and variants and have learned to adapt to get good prints. This is what I do and hopefully you can get as consistent results as I do with PETG, at least in terms of first few layers.
MK2S kit owner since 8/15/2017
Re: Second Layer print issues
I am aware of and pay heed to the smash bed adhesion issues of PETG. I run PETG on my other two printers as well, with very good results. On the Prusa, I have run several rolls of PETG. The only problem I usually have is the notorious "Hair" issue with PETG. On both the CEL Robox and the Ultimaker 3 extended, I have tweaked the settings so that I do not have that issue any longer. I am suing the same temperature settings on all three printers.
It almost appears that the first layer is too far from the print bed. If I watch it print it appears to be extruded above the bed and role down into place. Initial print speed is pretty slow, I am using the default setting for Prusa PETG. I did change the non-printing travel speed to max in an attempt to reduce the hairs that PETG leaves all over the print.
This all started when I replaced a couple of parts on the print head. The Fan Shroud and the Hot End body both warped and cracked due to heat. I reprinted them with eSun Carbon Fiber Nylon, left over from a previous print. Those prints came out great. After replacing them, I have been struggling to get PETG dialed back in. When I started the Z-offset was at around -.170, but I was having adhesion problems. I started adjusting the Z-offset until I got to a point it was sticking, but I still have the second layer issue.
I will try increasing the first layer temperature, But First layer is working pretty well. I can also leave the temperature the same for 2nd and 3rd layer to see if that helps.
Re: Second Layer print issues
Stringing seems unavoidable for PETG and it's blends but I've found fast retraction of 1-2mm with Linear Advance dialed in helped a lot only needing a couple blasts of hotgun to clean up. If no LA, I've tried 3-4mm retract but had so many nozzle clogs I never print PETG without LA. Some other things that might help is a relatively fast travel speed but with a lower acceleration to keep the nozzle moving and on-part as much as possible without loosing print speed or accuracy. This seems to help work around PETG elasticity issues.
What I've found and is obvious now that I think about it is, hot is strong, cold is detailed, with PETG, seems one must choose. Hopefully you have a slicer that can adjust per layer but better would be a slicer or firmware that can adapt nozzle temperature and speed/acceleration dynamically based on geometry analysis but that seems a dream at this point.
MK2S kit owner since 8/15/2017
Re: Second Layer print issues
I decided to start from scratch. I took your advise stephanpark, and re-calibrated the Penda Probe. I have a "Probe Calibration Tool" that I printed from Thingiverse. I used it last time, but tried it again anyway. it moved the probe up just a little. I then re-ran all of the calibrations and tests. I then loaded PLA and ran the "First Layer Calibration". This resulted in a z-offset of around -.327. I ran a small test print of PLA to make sure it was printing.
Following these steps, I then loaded PETG and ran a test print. i adjusted the z-offset to around -,310. This time I got a near perfect first and second layer. The first layer was perfectly smooth and did not exhibit the problem with the individual strands, everything was connected. The test print I ran was the same gcode I have been attempting to run, just to ensure everything is the same.
Bottom line; I am convinced something happened to the z-offset. Not sure why or what, but thankfully it is working again now. It only cost me 1/4 of a role of PETG 😕
Thanks for the help.
Robert
Re: Second Layer print issues
The Live Z will be different for different filaments, and should be re-adjusted if you change filament.
Why? Temp is different so the bed and nozzle will have expanded differently. The filament will flow differently due to different viscosities.
Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss. If you solve your problem, please post the solution…
Re: Second Layer print issues
The Live Z will be different for different filaments, and should be re-adjusted if you change filament.
Why? Temp is different so the bed and nozzle will have expanded differently. The filament will flow differently due to different viscosities.
I agree, that is why I keep a record of different Z-offsets for different material. They usually don't vary by much more than 0.05 - 0.1. The issue I had was much different. It reached a point that the z-offset adjust was having no effect. I was unable to adjust the z-axis low enough to correctly print.
A complete reset and re-calibration, after adjustment of the Penda seems to have fixed it.
As fate would have it though, I have been trying to print a particular model for a week. After the re-adjustment, it printed nearly perfect, not even any PETG stringing, until about half way through the print; then we experienced a power outage. .. so once again, I have to start the print over. 😈 👿