Random layer overextrusion "splurges"

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?

NitroFreak

I might have a glimpse.
What slicer are you using?
I had s3d once do an absolute extruder move on me while printing the prime tower, while the rest of the model was supposed to be in relative extrusion moves. It resulted in the prime tower being massively overextruded since on every new line, it wanted to extrude as much filament as all the previous lines combined.
Please try , in your slicer, enabling absolute extruder moves and allow zeroing the extruder moves (s3d)

Dezdoghound

So just for if anybody looks back to this from a google search and for documenting it solved this issue (don't worry it didn't take 4 months!).

At the time I was using a precision piezo on the hotend using the printed mount. The bowden coupler that I had wasn't holding the tube firmly enough (even with a collet clip in there), so when I was retracting, the tube was being pulled up and away from the hotend. When enough extruding was done to push the tube back down is where a splurge would occur.

I figured this out by marking the bowden tube with some pen, and watching it move slightly further out with each retraction. I've now changed the mounting method (and z homing method too) and all is well!