PETG overshooting at corners?

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ryaneb85
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PETG overshooting at corners?

Post by ryaneb85 » Fri Jan 08, 2016 6:43 am

Hi All,

I've been daring enough to move away from PLA and try out PETG, and while the majority of my print looks great (perfect first layer, other layers going down great without zits etc, no hairs/stringing, no nozzle build up), I seem to be getting some degree of what appears to be over shoot on sharp (~70-90 degree) turns. I don't get this on PLA, so I'm assuming it must be something to do with the PETG/PETG settings I am using. I am currently using a brand called QwikFab Q-PETG (white).

I did think it might be related to over-extruding, but I have calibrated my walls so as I am getting pretty much bang on 0.4mm thickness, so unless I am misunderstanding something, I don't think it is that. I also don't think its related to oozing when starting a new layer, as I've currently got my start points set to random and it seems to happen on corners even far away from the start point. If it's of any use, my retraction on start is currently set to -0.08.

That's about as far as my knowledge goes at the moment. Any ideas?

Ryan

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Matt_Sharkey
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Re: PETG overshooting at corners?

Post by Matt_Sharkey » Fri Jan 08, 2016 1:12 pm

What do you have set for your acceleration speeds? It may be the nozzle over driving the corners, and its only now manifesting on a pet g print.

your retraction should be fine, i think most people around here set retraction at 1.2mm and around 50mm/s.

Start points would have little to do with it. If you select align for the start points the slicer would try to start and stop at corner (concave ones if possible) but that would only effect one corner, not all.

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jimc
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Re: PETG overshooting at corners?

Post by jimc » Fri Jan 08, 2016 1:13 pm

Ryan can you post a pic showing this?

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PcS
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Re: PETG overshooting at corners?

Post by PcS » Fri Jan 08, 2016 3:27 pm

Print a simple one inch square one or two inches thick and start at your normal extruder temp and lower it each quarter inch of the print . After it is done you will notice better corners with lower temps. This has helped me with petg. It bonds like crazy at 255-260 but flows too easily. For some prints I run it as low as 220 and get good layer bonding with much sharper corners. I have found most smaller prints run better at 220. Larger ones with long straight extrusion runs need 255 or it will jam but smaller prints don't flow enough filament to cool the nozzle as fast as long straight extrusions do. In general the lowest extrusion temperature you can run and get good bonding usually produces sharper detail. At least for me ...in my experience . I am sure someone will state the exact oposite. :D :lol:

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Jules
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Re: PETG overshooting at corners?

Post by Jules » Fri Jan 08, 2016 4:06 pm

In general the lowest extrusion temperature you can run and get good bonding usually produces sharper detail.
Oh yeah, thanks for the reminder......I've been meaning to play with taking the temp down a bit on the PETG - not having any trouble with 240-245, but I do think it's a good idea to print the filaments at the lowest good bonding temp you can. :D

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ryaneb85
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Re: PETG overshooting at corners?

Post by ryaneb85 » Sat Jan 09, 2016 2:47 am

Ok, I think I might have cracked it. I did a couple of adjustments last night and left a print on overnight, and despite a little bit of ghosting, I think it's my best print thus far (including PLA). Here is what I changed:

- I bumped the extra restart distance down a little more to -0.09
- Put a very small amount of coasting on (0.01)
- Dropped the acceleration in the start code to M201 X1000 Y1000
- Noticed that although my perimeter walls were correct, the filament width was incorrectly set. I corrected this value and dialed in the extrusion multiplier. ( one thing I always notice is that 3 of the walls are almost identical, but one wall is - always slightly thinner)
- I did what JsC has mentioned and printed a 10cm high calibration cuboid (hollow with 1 perimeter) and varied nozzle temperature as it printed. The recommended print temperature for my filament is 240-200C, so I started at 240C and dropped 5C even 50 or so layers, so the very last section of the print was printing at 200C. I then picked the section of print that looked the best and felt the strongest, which happened to be at around 230C.

I like to print at 0.1mm layers (I'm all about the aesthetics), and this print came out almost seamless. I'll stick a bigger print on this morning to make sure it wasn't luck..

I need to try out some of the eSun that most of you guys use. The Qwikfab seems pretty decent stuff, but it's quite expensive and it's nice to have alternative options.

CCVirginia
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Re: PETG overshooting at corners?

Post by CCVirginia » Wed Feb 03, 2016 4:07 am

Sounds like you are doing great - could you post all the settings you are using? :?:

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willnewton
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Re: PETG overshooting at corners?

Post by willnewton » Wed Feb 03, 2016 3:47 pm

Do you think that your lower printing temp is related to your .10mm layer height?

Since you don't need to extrude as much filament in your preferred .10mm layer, the extruder moves a lower volume of plastic, therefore the filament stays in the hot zone longer. As a result you can print at lower temps than the average user printing .20mm layers at 240º-245ºish.

In a similar fashion, you could extrude at a lower temp with a slower XY print speed setting.

It would be a cool bit of software trickery to have automatic temperature compensation for print speed and layer height.
I'm finally back to where I started two days ago!

A thread with some stuff in it I update every once in a while. viewtopic.php?f=8&t=9
See some of my stuff http://www.thingiverse.com/willnewton/about

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ryaneb85
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Re: PETG overshooting at corners?

Post by ryaneb85 » Fri Feb 05, 2016 3:02 am

I'd rather not post my settings at the moment CCV - I'm tinkering with my hardware on an almost daily basis and the last change I made really screwed up my first layer, especially with PETG, so I've changed my settings so much since my last post and stupidly didn't make a backup, so I don't even know how they would print right now. As soon as I've got it where I need it to be again, I'll be more than happy to share.

Quite possibly Will. However, it seems that the recommended printing temperature for the PETG I am currently using (Qwikfabb) is lower than normal (220-240 if I remember correctly), so I just printed a calibration piece and varied the temperature within this range as it printed, then chose the best section. I also print at 50mm/s, which is quite slow. It would be interesting to test the eSun PETG at the same temp., speed and later height to see if the results were similar, or if it really is due to the filament.

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