Blobs at every start and end of line

DanL

Could it be a bowden related mechanical issue, e.g. the curvature or a slight kink or dent of the tube, a loose tube/end fitting connection, slight play in the tube-to-extruder fitting......?

dc42

Blobs at the end of a line are typically caused by lack of pressure advance or insufficient retraction. Blobs at the start of a line are not normal. Are you sure that you don't have a positive "extra restart distance" or similar configured in your slicer?

Jorge

@danl said in Blobs at every start and end of line:

Could it be a bowden related mechanical issue, e.g. the curvature or a slight kink or dent of the tube, a loose tube/end fitting connection, slight play in the tube-to-extruder fitting......?

I assumed something like that, too. The bowden is about 50 cm long, which is longer, than I'm used to. That's why I try made a test with a very short bowden, allowing me only to print on one corner of the print area. Again no difference.
Watching the tube-to-extruder fitting while printing didn't bring the enlightment, too.

@dc42 said in Blobs at every start and end of line:

Blobs at the end of a line are typically caused by lack of pressure advance or insufficient retraction. Blobs at the start of a line are not normal. Are you sure that you don't have a positive "extra restart distance" or similar configured in your slicer?

Makes sense. But I even set ...

@jorge said in Blobs at every start and end of line:

... a negative restart distance until I got a fatal underextrusion at the beginning of a line but though I have a blob. So first a blob and then underextrusion for a few mm. This confuses me a lot.

DanL

@jorge
I just looked at your S3D settings and you are not using the "Coast" setting.
For me, "Coast" is really helpful to control end blob. I know you tested Coast and Restart, but maybe look at that approach again?
I don't know if you have seen the info in the link below, but maybe helpful.
https://forum.simplify3d.com/viewtopic.php?f=8&t=2367

dc42

In theory, coast-to-end is a poor substitute for pressure advance, and is therefore not needed if you are using the right amount of pressure advance.

Jorge

Finally I found the time to change the board and it did not help. Same blobs with Marlin. So it has nothing to do with the Duet or RepRap Firmware which means it must be a mechanical issue. I am kind of happy about that, because I love everything about the Duet. But now I have no idea how to solve the problem.

Veti

From your config

M305 P0 T100000 B4138 R4700 ; Set thermistor + ADC parameters for heater 0
M305 P1 T100000 B4138 R4700 ; Set thermistor + ADC parameters for heater 1

B4138 is the default value and very likely the wrong value for your thermistor.
This can give vastly incorrect temperature differences. (in the range of 40C easily)

Jorge

Thank you for that clue! You were right! I had to calibrate P1 and landet at B3980. The hotend was more than 20C to hot (at 230C)! But since I tested a lot of different temperatures, this didn't help for my problem

Veti

what is the lowest temperature that you have printed pla at?

Veti

@jorge said in Blobs at every start and end of line:

Thank you for that clue! You were right! I had to calibrate P1 and landet at B3980. The hotend was more than 20C to hot (at 230C)! But since I tested a lot of different temperatures,

how did you do the calibration?
normally you find out what the thermistor is and put in the specified value for that thermistor into your config. B3980 is a very unusual value.

Jorge

I printed PLA at temperatures down to non extrusion.

I have a hotend from aliexpress. There was no B Value mentioned.
For the calibration I removed the filament and the bowden. Then I put the temperature sensor of my multimeter from the top into the nozzle. In the nozzle was some molten filament left, so there was a very good thermal connection to the nozzle. Then I set 230 °C and tweaked the value until the printer and the multimeter showed exactly the same value. I assume, that I eliminated any thermal transitions and tolerances this way, as I measured the temperature of the molten filament and not the heatblock or so.

Veti

can you link as to which hotend you bought.

but a random hotend can be a hit and miss.
there could be a quality problem in any of the parts that might cause the problems you are seeing.

Jorge

Unfortunately the link is no more active. Neither to the V6 clone nor to the cyclops clone or the NF hotend.
But most tests were made with the V6 clone.
I already ordered a coated heatbreak from mapa refining here in Germany and a new bowden. I think the heatsink has no effect as long as the heatbreak and the nozzle are good. And I have a lot of nozzles here.

Veti

@jorge said in Blobs at every start and end of line:

I think the heatsink has no effect

the bowden retention mechanism can have an effect. A small play can lead to retraction problems.

I.e. this heatsink from aliexpress is very close to the e3d one
https://www.aliexpress.com/item/32842829820.html
whereas this one is using a push fit connector which can fail after some time
https://www.aliexpress.com/item/32504536967.html