<p>Piecing this answer together from the comments on OP's post.
Myself and R.. noted that a layer height of 0.35&nbsp;mm, nozzle width of 1.2&nbsp;mm, and a fairly high feedrate (200&nbsp;% according to OP, no reference to what 100&nbsp;% is), is an exceptionally large amount of plastic to try and melt through almost any hotend on the market except possibly the Volcano, or the high-throughput version of the Mosquito. </p>

<p>OP responded that lowering the layer height to 0.2&nbsp;mm seemed to fix the issue. That's still an impressive amount of plastic, but it's a 43&nbsp;% decrease in total flow compared to 0.35&nbsp;mm layer height. </p>

CC BY-SA 4.0
2019-07-14T11:45:58.550Z
Addendunm: e3D Volcano and Supervolcano have doube/quadruple the meltzone length to gain access to extreme flow for extreme speeds. The only other type of extruder, that I could think of that manages this is a pellet type extruder, where the arbor is heated and offers similar access to high flow.
Trish
CC BY-SA 4.0
2019-07-14T03:38:15.500Z
2019-07-14T18:18:22.917Z
2019-07-14T18:18:22.917Z
Nach0z
<p>PET-G is the main filament I use. I can achieve high quality of my prints with my Prusa i3 mk3s printer. Recently however, I've recently changed my nozzle from the default 0.4mm to the 1.2mm. I watched the online video tutorial on how to do it properly and did the whole process carefully. </p>

<p>Temperature: 250&nbsp;&deg;C/100&nbsp;&deg;C
Speed: max 200&nbsp;%, but results are the same even all the higher ones&nbsp;.
Layer height: 0.35&nbsp;mm</p>

<p>With my first print (and the next ones too) on the new nozzle I noticed lots of under-extrusion with infill (holes). LOTS of stringing although I've increased retraction. What's the reason ? </p>

CC BY-SA 4.0
2019-07-10T21:37:28.767Z
What speed, layer height and temperature are you using? You have just increased the cross-section of the nozzle by 800%. It is possible that the hot end is not able to extrude the filament at the rate that you are requesting.
Mick
CC BY-SA 4.0
2019-07-10T21:41:54.050Z
@Mick I'm sorry, I've forgotten to add this, I usually include such information. I will edit my question
StLuke5
CC BY-SA 4.0
2019-07-11T00:09:46.957Z
Can your hotend melt PETG at the rate you're printing? You need a **hardcore** hotend to take advantage of that nozzle size without really low speeds. Assuming you don't need the wall thickness, 0.4 can probably even print faster with a normal hotend.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-07-11T08:09:54.940Z
"200%" doesn't seem like much of a valid speed - unless the Prusa i3 has some sort of default speed everyone is using?

At the same layer height, you can only move 1/3 as quickly as with a 0.4 mm nozzle - your hot end has to melt *much* more plastic at the same speed.
Since you also went to a layer height of 0.35 (with the default presumably being 0.2mm), you're now extrusing 5.25x as much plastic in the same time. Your hot end probably just can't keep up.
towe
CC BY-SA 4.0
2019-07-11T10:28:16.270Z
@Towe Prusa says that speeds up to 200% are OK. But  I'll try switching the layer height to 0.2mm
StLuke5
CC BY-SA 4.0
2019-07-11T10:46:26.130Z
@StLuke5 Well, 200% of what sort of default speed? That would have to be a figure of something like "40 mm/s" or "2400 mm/min" (in ancient slicers).
towe
CC BY-SA 4.0
2019-07-13T00:38:30.733Z
Having struggled with PETG myself, using a V6 with a 0.4mm nozzle, I can say with a fair amount of confidence that printing lines 1.2mm across and greater at 0.35mm layer height, at feedrate faster than a snail's pace, is simply outside the capabilities of your hotend. That is an absurd amount of plastic to melt in that kind of time period. You'd probably benefit from upgrading to possibly a Volcano hotend if you want that kind of performance from your printer.
Nach0z
CC BY-SA 4.0
2019-07-13T18:24:51.573Z
@Nach0z Thanks, decreasing the layer height to 0.2mm worked for me.
StLuke5
<print-quality><prusa-i3><3d-models><petg><underextrusion>
PET-G under-extrusion after changing the nozzle to a 1.2 mm d. one (Prusa i3 mk3s and PrusaSlicer v2.0)
StLuke5
# PET-G under-extrusion after changing the nozzle to a 1.2 mm d. one (Prusa i3 mk3s and PrusaSlicer v2.0)

(Asked by: username_0 on 2019-07-10)

PET-G is the main filament I use. I can achieve high quality of my prints with my Prusa i3 mk3s printer. Recently however, I've recently changed my nozzle from the default 0.4mm to the 1.2mm. I watched the online video tutorial on how to do it properly and did the whole process carefully.

Temperature: 250 °C/100 °C
Speed: max 200 %, but results are the same even all the higher ones .
Layer height: 0.35 mm

With my first print (and the next ones too) on the new nozzle I noticed lots of under-extrusion with infill (holes). LOTS of stringing although I've increased retraction. What's the reason ?

**Tags:** print-quality, prusa-i3, 3d-models, petg, underextrusion
> **Comments:**
> **username_1**: What speed, layer height and temperature are you using? You have just increased the cross-section of the nozzle by 800%. It is possible that the hot end is not able to extrude the filament at the rate that you are requesting.  
> **username_0**: @Mick I'm sorry, I've forgotten to add this, I usually include such information. I will edit my question  
> **username_2**: Can your hotend melt PETG at the rate you're printing? You need a **hardcore** hotend to take advantage of that nozzle size without really low speeds. Assuming you don't need the wall thickness, 0.4 can probably even print faster with a normal hotend.  
> **username_3**: "200%" doesn't seem like much of a valid speed - unless the Prusa i3 has some sort of default speed everyone is using?  At the same layer height, you can only move 1/3 as quickly as with a 0.4 mm nozzle - your hot end has to melt *much* more plastic at the same speed. Since you also went to a layer height of 0.35 (with the default presumably being 0.2mm), you're now extrusing 5.25x as much plastic in the same time. Your hot end probably just can't keep up.  
> **username_0**: @Towe Prusa says that speeds up to 200% are OK. But  I'll try switching the layer height to 0.2mm  
> **username_3**: @StLuke5 Well, 200% of what sort of default speed? That would have to be a figure of something like "40 mm/s" or "2400 mm/min" (in ancient slicers).  
> **username_4**: Having struggled with PETG myself, using a V6 with a 0.4mm nozzle, I can say with a fair amount of confidence that printing lines 1.2mm across and greater at 0.35mm layer height, at feedrate faster than a snail's pace, is simply outside the capabilities of your hotend. That is an absurd amount of plastic to melt in that kind of time period. You'd probably benefit from upgrading to possibly a Volcano hotend if you want that kind of performance from your printer.  
> **username_0**: @Nach0z Thanks, decreasing the layer height to 0.2mm worked for me.  

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## 1 answers

### Answer by username_4 on 2019-07-14. Score: 4 | Accepted answer

Piecing this answer together from the comments on OP's post.
Myself and R.. noted that a layer height of 0.35 mm, nozzle width of 1.2 mm, and a fairly high feedrate (200 % according to OP, no reference to what 100 % is), is an exceptionally large amount of plastic to try and melt through almost any hotend on the market except possibly the Volcano, or the high-throughput version of the Mosquito.

OP responded that lowering the layer height to 0.2 mm seemed to fix the issue. That's still an impressive amount of plastic, but it's a 43 % decrease in total flow compared to 0.35 mm layer height.

> **Comments:**
> **username_5**: Addendunm: e3D Volcano and Supervolcano have doube/quadruple the meltzone length to gain access to extreme flow for extreme speeds. The only other type of extruder, that I could think of that manages this is a pellet type extruder, where the arbor is heated and offers similar access to high flow.  

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