3d Printing with PETg (why I’m a fan)

By | April 8, 2017

… or maybe fan is the wrong word as you’ll see …

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I’d never had much luck with the fans that came with my other wise high quality printer, alas they only ever produced a very weak barely noticeable stream of air.  This had the biggest impact when printing highly angled overhangs with PLA.  While you can often get away with angles nearly 45 degrees away from vertical, much more and I’d quickly run into problems with the recently printed layers warping upwards, so much so that parts of a model could be parted from the bed by the nozzle itself.  I noticed particularly issues when attempting a Celtic knot model I’d created with OpenSCAD, this features overhangs from mild to quite extreme!  I tried a couple of techniques but soon realised without a replacement for the fans I was getting nowhere.  I’d never been too keen on trying ABS for a number of reasons, but was sure that it would be worth trying other materials than just PLA.  After some research, procrastination, and further research I decided that PETg was a candidate of interest.  Having need of a higher temperature than PLA I did have a small concern that it might be a difficult material to use, however when feeding the PETg into the nozzle at a temperature of only 220c the filament melted easily and fed through the nozzle quite easily so that did give some reassurance.

I managed to find some “natural” uncoloured filament from ebay manufactured by real filament while this wasn’t great value (nearly £20 for a 1 KG reel, where you can easily find PLA for half that) given the advantages of PETg I can only hope more people start using it and that brings the price to a fairer level.

Lets get the negatives out of the way, I did try printing on a “cold” bed – the packaging claims “20-35 degrees Celsius, but not necessary” but there are definitely cases where you need a heated bed.  I printed out a thin key fob, which was just 1mm thick and it had a noticeably bad warping which is probably no great surprise, however I’d previously printed a very similar key fob but I’d forgotten to turn the bed off (it was left at 60C) and that printed perfectly, and the 1mm thick surround looks almost transparent (230C print temp – must try higher to see if it gets more transparent) with the 1mm font on top, the few people who have seen it up close were impressed with how it looked.  PETg is noticeably much more flexible than PLA, so it should be much better for snap together connections than PLA, however as I discovered attempting to unwarp a piece of PETg it will fail suddenly, I do wonder if heating with a very hot hair drier might allow some manual unwarping or shaping of printed PETg.  Printing the larger Celtic knot with a bed temperature of 35C I noticed some slight warping on a part of one of one of the three bases (each of the bases are approximately the size of a (UK) ten pence piece) so I will try 40C next for the bed temperature.

Now for the good stuff (you deserve it if you’ve got this far! 🙂 )  I’d previously touched on warping and PETg is everything I’d hoped it might be, the only very slight issue I’ve seen is with a very extreme overhang just before bridging two parts of a particular model, and this was without the use of fans, yes that’s right you can print really quite extreme overhangs without needing a fan, and I rather do suspect that with a strong fan you could get near perfect results.  That said for normal use PETg behaves so well, a fan is completely unnecessary and being as I melted a corner of one of my fan shrouds I’ve removed them completely.

So I still have to dial in more exact temperatures but I’m in the right ball park, and this material is without doubt an improvement on PLA, I’d strongly recommend that when your current reel is about to run out you give PETg a go, it is far more forgiving than PLA…

Oh if you’re wondering why the small knot looks a so roapy its, because its just 2cm at widest point and printed with a .25mm layer height, while the “low” resolution works very well for larger models (giving larger volume per layer for infill – so it can get into thin features) for smaller models (the tube shape is just 3mm wide) you do need a higher layer resolution, that said the larger knot is printed with a .25mm layer size and the slopes are lovely and smooth…

One final point, just print on any old cheap masking tape (which is no different from “blue painters tape” lets face it!) and PETg will stick really well, you can use a heated bed with masking tape too…

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