PETG printing parameters

[Andrew Aurigema]

Has anybody got a set of MBI Replicator 2X parameters that will work for PETG ???   I got a couple of test rolls of ORB Poly PETG ( 1.75mm ) and can not for the life of my printer figure out what it takes to get that stuff to print correctly.  

I have tried 220, 225, 230, 235 C with hot and cold build platforms.  It always seems to go to air print after a few minutes.  It seems to want to work better hotter but it still fails due to heat creap ( I think ).  

I have 2500 + hrs of ABS printing so I know it is not my printer.  

Drew in sunny FLA  

[Ryan Carlyle]

Go hotter. Try 245C. And recalibrate your extrusion multiplier. (What slicer?) In my opinion you need to under-extrude PETG a bit to get clean and reliable results.

[Andrew Aurigema]

I use Simplfy 3D as the slicer.  What is "under-extrude" ???  

Is it like tell the software the filament diameter is 1.8 mm so it calculates a lesser amount of turn on the feed motors for any given amount of travel ???

Seems like going hotter will just make the heat creep worse and fail the print faster.  

Have you actually got this stuff to print out and nice objects ???

[Gian Pablo]

Yeah, definitely go hotter. Colorfabb nGen works well at 240C but other PETG formulations need to go as high as 260C. Print bed temperature can be lower than for ABS. Colorfabb nGen at 80C is good, and other formulations can go as low as 50C. When using PETG I print on the green PET tape, which has been lightly sanded to improve grip. The group is so good that I need to tram the bed very carefully, so that plastic is NOT squishing down and spreading.

Thermal creep is certainly an issue with the 2X, more than with the Rep 1. 

I worked around this in two ways:

1. Use higher layer heights, to keep filament flowing through faster (eg. 0.3mm or 0.4mm layer heights) - certainly do this at first until you get used to the material
2. Improve cooling (I installed higher CFM fans connected to an external power supply, and vary the voltage according to the material I'm using)

[Gian Pablo]

Interesting. I had to over-extrude by about 2% to get good results with nGen, my top surfaces seemed a bit sparse otherwise.

[Scott Booker]

You'll probably want to leave the top cover off, and the front door open.  On an R2X the heat creep can kill PET prints (I use PET+ quite a bit).  Running a "hot" chamber is not required for this material.

[Gian Pablo]

+1

Keeping the covers open and hood off is essential.

[Andrew Aurigema]

PETG :  So to put it all together, 240 C or hotter on the extrusion temp, with the door open and top off ( maybe even extra cooling not a bad thing )  so the system cools, pay attention to heat creep from the extruder,  cooler bed ( 80 C or so ) with blue painters tape or PET tape , and maybe 2% overextrude.  

Thanks for all the inputs.  

[Ryan Carlyle]

Don't over-extrude. Do the proper 20mm calibration cube technique to find the "correct" extrusion multiplier, then lower that down a bit to keep filament from blobbing on the nozzle.