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PETG advice

Posted by racitup 
PETG advice
July 05, 2023 02:57PM
Hi again,

Another thing I'd like to do with the Fisher Delta is print with PETG.

I have had a brief try and it went okay, but it didn't completely adhere to the bed at 85degC and warped as a result, so I will try 90degC next.
But the two bad things that happened:
1. The head ducts melted
2. The nozzle got completely blocked

I think this was because I directed a small fan heater at the head to try to increase the ambient temperature so the whole thing overheated.

The things I'm going to try:
* Move the heater a bit further away
* 90degC bed temperature
* Leave the head ducts off
* Dry the filament

Does anyone else have experience of printing PETG on a Fisher Delta and have any advice?
Do you think I have any chance with my approach and without a heated chamber?

Thanks in advance,
Re: PETG advice
July 05, 2023 03:53PM
PETG doesn't need a heated chamber. On my delta (not a Fisher) I use 80C bed temperature. I reduce the maximum speed of the print cooling fan to about 40%.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: PETG advice
July 05, 2023 09:57PM
Okay thanks, that gives me some hope.

Unfortunately on a Fisher (or at least the one I'm using; an old Duet 0.6) the fan speed doesn't change. I guess it may have been wired up wrong though.

I'm hoping leaving the head ducts off (that direct the airflow directly towards the nozzle) it will have a similar effect to reducing the fan speed and keeping the print hotter for longer
Re: PETG advice
July 06, 2023 01:19AM
Even with a Duet 0.6 you should be able to control the speed of the fans unless they are stuck permanently on.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: PETG advice
July 07, 2023 12:49PM
I think because it's not a full metal hot end, the heatsink needs the fan permanently on so the main PLA head part doesn't melt

For anyone else looking for PETG advice:

* I don't recommend removing the fan ducts, they don't seem to make a difference to the print other than they may prevent/cool plastic that is stuck to the outside of the nozzle meaning it doesn't oxidise and fall off into the print leaving ugly brown streaks
* It's very important to reduce the first layer speed a lot. On very small parts I needed 20%. I probably wouldn't go above 50% at all
* I did eventually get 80degC bed temperature working with a 250degC nozzle temperature. I was using 230degC before and I think the hotter filament compensates for the cooler bed. I read an article saying 250degC is best for PETG in terms of strength. The manufacturer recommended 230degC
* I'm now trying a glue on the bed. It is covered with kapton tape, and on top of that I'm painting on a 50:50 mix of PVA glue and water, that I read works instead of all these expensive glues around. It certainly hasn't made things worse and I think just gives the bed a bit of a matt surface finish that helps. Before that I tried a 600 grit sandpaper on the tape surface which I think probably helped
* I haven't tried the external heater again but am trying to prevent draughts
* Drying the filament certainly hasn't made things worse either
* Good quality filament will help. I inherited a reel of PLA that is awful. It literally has lumps of brown plastic moulded into the filament randomly which would cause a jam and block the nozzle, which obviously doesn't help with print anxiety!
* Obviously getting the print height consistent across the whole bed is vital, so make sure you do the mesh grid compensation and calibration with the nozzle hot. I have a raised spot opposite a tower which I don't really understand

Initial results are promising, and it's not that much harder to print than PLA smiling smiley
Re: PETG advice
July 10, 2023 12:59PM
More advice:

* I'm now using a 2:1 mix of PVA glue and water, works fine!
* the residual print warping issue was due to an unlevel print head, caused by the PLA part being warped. NOTE: that the cooling fan on the print head has only one screw and can easily be hinged up causing no airflow over the heatsink. This WILL warp your print head!
* Further to the fan ducts, I believe they are there to help with bridging, so definitely don't remove them
* Fill density helps a lot too. Just a raise from 20% to 30% using star infill made a huge difference to warping and strength
* Also important to get your print speeds dialled in, experiment and watch the print. The slower you go the better the print, unless it's bridging!
* I'm having trouble with adaptive slicing, so switch that off...
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