Blobs at every start and end of line

Nightreaver

OT: You left your wifi password in there?

dc42

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

So my current aim is to get the new printer to print those simple bodys as good as my other printers without retraction and actually without pressure advance. Only afterwards I wanted to calibrate retraction. Do you agree or am I on the wrong track?

IMO you are on the wrong track. Using a Bowden extruder, if you don't retract on layer change and you don't use pressure advance, you will get a blob unless the layer change happens very fast. Likewise if you don't retract before a travel move.

Are you absolutely certain that you were not using any retraction or pressure advance on your other printer? Retraction may be done by the slicer generating direct retraction commands, or by the slicer generating high-level commands, or perhaps by the firmware.

Jorge

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

OT: You left your wifi password in there?

Thats an old password, so no worries
But I just deleted ist though.

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

IMO you are on the wrong track. Using a Bowden extruder, if you don't retract on layer change and you don't use pressure advance, you will get a blob unless the layer change happens very fast. Likewise if you don't retract before a travel move.
Are you absolutely certain that you were not using any retraction or pressure advance on your other printer? Retraction may be done by the slicer generating direct retraction commands, or by the slicer generating high-level commands, or perhaps by the firmware.

Yes, pressure advance is deactivated for sure. And the GCODE was the same file. So there is no retraction in the GCODE. I double-checked it in a text editor. I have Marlin running on the other printer. I never heard, that it is doing any retraction or so by firmware?

Here is one more test: I printed the same body again, once at the same speed as before (travel= 500mm/s, Infill = 60 mm/s, perimeter and testline = 45 mm/s), and once at 20% speed.

It's interesting, that the infill of the faster one is underextruded compared to the slower one, even though 60 mm/s is not so fast. And obviously the blob almost disappeared at the slower one. I conclude that the hotend must be not slippy enough and there must rise a big pressure in the bowden. With this pressure even the shortest stop is enough to build this blob. Maybe the hotend of the other printer is kind of slippier, so that less pressure grows when printing at 60 mm/s? Maybe I should try one more hotend or just an other nozzle? What do you think?

Phaedrux

This may be more trouble than you're willing to expend, but perhaps you could swap the Duet and the board running Marlin in order to eliminate hardware differences.

dc42

Another thing you could try is installing firmware 2.03 and setting the jerk policy to 1 in the M566 command. That works more like Marlin does, by allowing jerk to be used where it isn't needed in theory, e.g. between a travel move and an extruding move.

Jorge

I updated the firmware but unfortunately it makes no difference.
Next I will test it with a simple 8 bit board with Marlin. I hope it makes no difference because I really like the duet and the Dibond housing is milled for it...

Jorge

I did not find the time to change the board yet but I did some coasting and restart distance tests. I set a high coasting distance and 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.

dc42

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

I updated the firmware but unfortunately it makes no difference.

But did you also set the jerk policy to 1 ?

Jorge

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

But did you also set the jerk policy to 1 ?

Yes, no visible difference

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.