3D printing with PET

This week I’ve been working with the PET (Polyethylene terephthalate) filaments from Refil. It’s made from recycled bottles and no additional colouring is added so it comes in a limited range of colours. I got a sample pack which has some blue, green, clear and mixed. I quite like the mixed which comes out a kind of pale grey colour.

It has slightly different properties than the other filaments I’ve previously worked with (ABS and PLA).

  • Bed Adhesion: This not as good as I get with PLA and ABS so a brim is recommended, particularly on thin items.
  • Stringing: This manifests itself in two ways, firsly when the Cel Robox does its mini purge at the start the filament can curl up and stick to the print head. This then can catch on other things as it is printing causing failures. So you do need to watch out for this and pause the printer to remove it before printing starts. There can also be stringing when printing but mostly this is kept in check by the Robox’s needle valves.
  • Spanning: PET does not seem to span well, when stretched across a gap it goes very thin and then deposits a blob when it hits something on the other side. I’ve mostly seen this when printing larger items with a lower fill percentage as it is the absolute width that is spanned not the percentage that is important. When the printer comes to print the top layers it ends up blobish and messy. Increasing the temperature has helped with this but I don’t want to raise it too high and burn the plastic. Spanning should be kept short, to only a 5-10mm max.

Robox Automaker Settings

PET does seem quite sensitive to drafts even with the enclosed prints space on the Robox. One print seemed to producing a poor result until I shut the backdoor and raised the bed and nozzle temperatures up a fraction to give a high ambient temperature.

Following a number of PET prints, I moved on the some ABS also from Refil which is black because it is made from old car dashboards. Whilst this was printing I noticed strange clear blobs hanging off the print head. I paused the print and remove them, there was quite a lot of material and I actually paused the printer three times to clear it all. I’m guessing that the PET had accumulated up there when doing the purges. I had done quite a number of print but even so I was surprised by the quantity.

So the PET filament does produce good results and strong and stable parts so I’m likely to get more when the sample pack runs out. But I will be definately be checking the print head following the prints to make sure I don’t get any more suprises.

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