Random layer overextrusion "splurges"

Dezdoghound

Ok, so I thought it could be that the airflow wasn't enough, as my current hotend design is like this with two blower fans on the side, so there isn't much room to exhaust the warm air.

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However, I've tried some string test pyramids (https://www.thingiverse.com/thing:2219103) with one of the blowers off so there is better airflow and it always has the same "splurge" on the same layer (approx 30). The heatsink also doesn't feel noticably warm at this point, (measured 31°C).

I've done a run of the pyramids with retraction off (pressure advance at 0.45 still on) and it comes out perfectly (minus stringing artefacts)

I've tried printing at a series of temps and it still happened at 190°C with the prusament.

@Phaedrux I've also attached my config.g and a 3mf file

Things to try:

@Phaedrux I'll do a run with the fan flipped to see if that lowers the temp any better
titanium heat break when that arrives
config_dez.g

[0_1573682209187_string_test_fast_pyramid.3mf](Uploading 100%)

Phaedrux

The .3mf didn't upload. Perhaps too large. Might have to host it on dropbox or similar.

Dezdoghound

@Phaedrux https://www.dropbox.com/s/7a48czp4cj1bjti/string_test_fast_pyramid.3mf?dl=0

There's a link to the 3mf file. Let me know what you think. Don't think it's slicer related as prusa slicer does it too, although on different layers.

Phaedrux

I don't see anything abnormal in the gcode file or slicer settings.

The prusament has some glitter flecks in it, does it not? I wonder if you're getting some minor clogs and pressure build up that gets released as a blob?

Dezdoghound

I don't think so, as this happens with other filaments too. This is still an issue for me. I've tried disassembling and cleaning the hotend, redoing the hot tighten on the nozzle and it still happens.

This example happened today, after doing the first layer sucessfully, it began to underextrude, then a massive splurge came out at once. It's like it's getting behind on extrusion so then trying to catch up by extruding loads?

This happened on the second layer so there's no way it's insufficient cooling on the heatbreak. This was being printed at 215, 30 mm/s 0.12 layer height.

I'd really appreciate any more help from anybody.
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Phaedrux

What happens if you extrude continuously into free air?

Dezdoghound

@Phaedrux I then get a constant extrusion of plastic. It is quite a leaky extruder, but it does give constant amounts of material.

Phaedrux

Leaky extruder?

Dezdoghound

@Phaedrux sorry by that I mean the nozzle leaks when I'm not extruding anything.

droftarts

Please post your config.g, or at least your thermistor settings, and what thermistor you actually have. I'd say you are printing too hot, so the filament is melting too far up the chamber, and eventually a pool of filament eventually leaks out. If your thermistor settings are incorrect, you don't really know what temperature you are extruding at. Extruding into air doesn't tell you much, because generally you extrude much faster into air than you would during a print.

Ian

Dezdoghound

@droftarts Prusament says that the temperature range is 210 ± 10 °C. I have also tried printing at 190 and I find the same issue. The issue also happens on the first layer, so it's unlikely that it's a heat creep issue.

I suspect the thermistor is fine as it reads room temperature to within 2°, and at ambient shows the same as the bed to within 0.5°.

Here's a link to my config.g

https://www.dropbox.com/s/ztt6oe6roz4yvqx/config_dez.g?dl=0

bartolomeus

I've been having problems with prusament today as well. Nozzle jams at the same point in a print every time, even after changing retraction and print temps. After searching around, it seems that this filament causes quite some jamming problems.

droftarts

@Dezdoghound From your config.g:

; Heaters
M305 P0 T100000 B4138 C0 R4700      ; Set thermistor + ADC parameters for heater 0
M143 H0 S120                        ; Set temperature limit for heater 0 to 120C
M305 P1 T100000 B4138 C0 R4700      ; Set thermistor + ADC parameters for heater 1
M143 H1 S280                        ; Set temperature limit for heater 1 to 280C

These are the default thermistor settings, for a Honeywell 135-104QAD-J01 thermistor that shipped with hot ends from RepRapPro, who have been out of business for 4 years! So I doubt you have the correct thermistor settings. You have the same thermistor set for the bed, so not surprising the readings are close. And it will read accurately at ambient because all 100k ohm thermistors have a resistance of 100k ohms at 25C! But they report very differently as they get hotter. So please check what thermistors you have, and set them correctly, then you have a chance of accurately setting extrusion temperature.

Ian

Dezdoghound

@droftarts Ok, how can I verify what thermistors I have? They are the ones that came with the hotend from aliexpress.

droftarts

@Dezdoghound have you got a link to the item you bought?

Ian

Dezdoghound

@droftarts
This is the item that I got. NTC 3950 is what it says. From the PT1000 page, does that mean I should be using R4700, T100000, B3950 ?

https://www.aliexpress.com/item/32843399231.html?spm=a2g0s.9042311.0.0.27424c4dIPGEo0

Veti

B3950 is the value you should start with.

However the B3950 only refers to the temperature range of 25-50.
Unortunantly at higher ranges they thed to vary wildly depending on manufacturer.

if you order from aliexpress i would recommend triangelab.
they provide high quality equipment for 3d printers.
for example
https://de.aliexpress.com/item/32844028127.html?spm=a2g0x.12010612.8148356.2.702995f97zTe5Q
they use semitec 104-gt2 thermistors. same as e3d.

Dezdoghound

@Veti @droftarts So I've changed the thermistor values. I've also swapped to a genuine e3d titanium heat brake. Unfortunately I'm still getting the same issues of random overextrusions!

Veti

have you tried printing at 200 or 190C?

bartolomeus

@Dezdoghound said in Random layer overextrusion "splurges":

I've done a run of the pyramids with retraction off (pressure advance at 0.45 still on) and it comes out perfectly (minus stringing artefacts)

Have you also tried it the other way, with PA off?