So far its been almost two weeks since I started using PETG and I’ve resolved a lot of the problems I was experiencing in my last update.
Bed Adhesion Perfected
My prints are no longer becoming completely stuck to the print bed. Now, I can easily peel the completed print from the bed once it has cooled to about 45°C. Removing the print is almost trivial in how easy it is to do.
To achieve this, the first layer settings are very different to that of ABS. Smearing the filament into the bed is the wrong approach. It leads to nozzle jams and adhesion that causes the print to break. Instead, I have found that a first layer height of 105% of first layer thickness is needed. The extruded filament literally is laid down onto the bed. It looks as if it has no chance of adhering, however it is working perfectly.
Return of the Jam
After waxing lyrical previously how I’d fixed my nozzle jams by increasing the first layer height and reducing print speed, nozzle jams returned. They became quite significant. I was about 50% of the way into a print when they began occurring and I tried to salvage the print. Each time a jam occurred, I’d pause, remove the filament, cut the damaged filament off and insert it again and continue on.
Needless to say the print was rubbish, but watching the print closely, I attributed the jamming to retraction.
Currently I have retraction disabled and I have not encountered any jams since. However, the prints I have been making since have not required much retraction.
Long term I do think having retraction disabled is a good idea. Going forward, I think I will need to spend some time on tuning the retraction settings.
Surface Finish Improved
The next big improvement occurred a bit by chance. In an attempt to improve the dimensional accuracy of my prints I decided to print some small calibration blocks. In the process of doing this, I decided to measure the diameter of some extruded filament the was extruded following a filament change. I expected the extruded plastic in the birdsnest of filament to have a diameter close to 0.4mm because that is the rated diameter of my nozzle.
However, I was surprised to find that it was 0.48mm. Multiple measurements confirmed that filament being extruded from my printer is in fact 0.48mm. Has my nozzle begun to wear, or has its diameter always been this large? Or does the filament expand in diameter after it has been extruded?
When I adjusted my printer settings to account for what appears to be a larger nozzle diameter, I began to notice improvements to the surface finish of my single wall test prints. Fewer gaps were present in each layer and I was printing longer, more consistent layers.
Also, the average diameter of my filament is 1.70mm rather than 1.75mm. An average filament diameter was determined from all of the off-cut pieces of filament I had saved after clearing each jam.
Since adjusting the filament diameter to 1.70mm and increasing the nozzle diameter to 0.48mm, I have seen a huge improvement in surface finish. Now I am achieving distinct and smooth individual layers. The improvement can be seen in the following prints.
Final Thoughts
PETG is requiring more tuning than I expected, however the benefits of zero preparation for the first layer, increased print strength and odour free printing is worth the effort.
Future efforts will focus on trying to further improve surface finish by tuning the retraction settings.
SteelCity Electronics 