PETG Breakages

It’s been just over 1 week since I started using PETG instead of ABS.

I am very impressed with its performance. There have been a few print problems, however I have managed to identify and rectify some of these problems.

Nozzle Jamming

In my last post I mentioned that I was encountering nozzle jamming problems. I have managed to resolve this problem. I identified two situations that were causing the nozzle to jam; during the first layer and when printing infill.

Whilst printing the first layer, I had left the first layer height setting at “80% of layer height” which I normally use for ABS to ensure reliable bed adhesion. However, it appears the PETG requires at least 100% first layer height to allow for the extruded filament to flow from the nozzle and not back up.

Secondly, I was noticing when infill was being printed, I was encountering jamming. When printing infill, my printer was printing at 30mm/s. Reducing the print speed down to  25mm/s has not resulted in a jammed nozzle yet. I have noticed the extruder driver begin clicking when operating at 25mm/s so there maybe scope to decrease the print speed a little further.

Excess Stringing

My first few prints resulted in a lot of very fine stringing of plastic. It was very fine, almost like cobwebs all over the print.

It wasn’t causing any problems because it was very easy to remove. I could literally wipe it off with my finger.

To try to resolve this problem, I increased the retraction distance from 2mm to 7mm. However I saw no reduction in stringing and I think I may have been causing some nozzle jamming problems too. I have since returned the retraction distance back to 2mm.

Reducing the extruder temperature from 245°C to 240°C has resulted in a significant reduction in stringing. Some stringing still does remain however it is a fraction of what I was initially encountering. There may be scope to decrease the extruder temperature a little further to hopefully eliminate all of the stringing.

img_5264_petg_stringing
An example of the fine stringing that is occurring with PETG. This piece was printed with an extruder temperature of 240C.

Prints Stuck to Bed

My prints are becoming completely stuck to the bed at the moment. The excellent adherence of the PETG directly to my glass heated bed is becoming a real problem.

So far I have managed to tear the bottom layer off two prints. I have never had this problem before.

I have increased the first layer height to 100% (to resolve the nozzle jamming problem) and this has not helped.

img_5255
Print breakage when removing form the bed. Print settings were 245C extruder, 80C bed temperature with 100% first layer height.

Also, I’ve reduced the bed temperature from 80°C to 70°C and this has not helped either.

img_5257
Print breakage when removing form the bed. Print settings were 240C extruder, 70C bed temperature with 100% first layer height.

My next test to try and prevent breakage will increase the first layer height to 105%. I may even try using a wide paint scraper with a thin blade thickness.

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