Retraction calibration issues printing with my Prusa

Hello World!

This is my first post on the RepRap forums

I have finally finished setting up my Prusa Mendel printer, but I have been having trouble perfecting my prints due to an issue with my extruder retraction. The problem is that during non-print moves the extruder is not retracting filament. However, after the non-print move is completed, the extruder extrudes an extra length of filament to compensate for the length of filament that should have been retracted. Since the the filament is not initially retracted, each non-print move results in extra filament being extruded, which makes my prints look like bloated blobs of plastic. I have no idea how to fix this.

Here is some background information.

I am using RAMPS+Pollulu Motor Drivers, Repetier Host Firmware, Slic3r, Wade's Extruder, and MK2 Heatbed with Glass surface covered in green tape.

Print Settings:

Nozzle Diameter: 0.34 mm
Filament Size: 1.75 mm

Perimeters: 25 mm/s
Small Perimeters: 20 mm/s
External Perimeters: 100%
Infill: 30 mm/s
Solid Infill: 25 mm/s
Top Solid Infill: 50%
Bridges: 20 mm/s
Travel: 50 mm/s
First Layer: 50%

Fill Density: 0.2

------------------------------------Attempt#1--------------------------------------

Ok, so for my first print, I did not change the default much so my retraction settings looked like this:

-----Retraction-----

Length: 2.5 mm
Speed: 30 mm/s
Extra length on Restart: 0 mm
Min Travel after Retraction: 2 mm

The result was not pretty. Here is a picture of my first print:

[www.flickr.com]

------------------------------------Attempt#2--------------------------------------

After printing another blob, I deduced that the problem was that too much filament was being extruded to compensate for retraction during printing. Oddly, my setting for "Extra Length on Restart" (after retraction) was set to zero. This did not make sense, so I decided to avoid the problem altogether by simply disabling retraction. The result was great other than the strings of plastic left all over the part. This imperfection was something that was supposed to be solved by using retraction during printing.

Here is a picture of my second print with retraction disabled:

[www.flickr.com]

----------------------------------------Attempt#3--------------------------------------

I decided to try to calibrate my retraction settings once again to fix the problem of strings all over my print. My attempt at printing with mild retraction. The picture says it all... A blob-like print with strings of plastic all over it. In short, neither problem was solved.

-----Retraction-----

Length: 1.5 mm
Speed: 30mm/s (I have tried different speeds with the same result)
Extra Length on Restart: 0 mm
Min Travel after Retraction: 2 mm

Here is the picture:

[www.flickr.com]

...and here are a few more detailed pictures:

[www.flickr.com]

[www.flickr.com]

[www.flickr.com]

Finally, here is a (mediocre quality) video of my Prusa printing Attempt#3 that illustrates the problem:

[www.youtube.com]

-------------------------------------

At this point, I have no idea what is wrong with my printer. Is it my firmware? Is it Slic3r? It seems like my printer cannot retract during printing, even though I can easily retract filament using the manual control interface. I hope I gave enough information for you guys to understand what my problem is. I really hope someone can help me fix this.

Thanks in advance to the RepRap community for being so supportive!

Eric

You never mention the version of Slic3r you are using. I know one release had a bug that did something very similar.

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

You also don't mention what hot end you're using. A hot end with a large melt zone can have retraction issues, but not usually in the way you're getting.

However, every little bit of information helps.

Is the hardware working correctly? If you connect to your printer with pronterface and click on the extrude and retract button, can you both extract and retract?

Check that you have retraction disabled in either Repetier Host/Firmware or Slic3r. Your problem may be that you have both Repetier Host/Firmware and Slic3r set for retraction. You should use only one or the other - not both.

Edited 1 time(s). Last edit at 09/26/2012 07:57AM by davejones.

First of all, thanks to everyone for their input.

@Alagi: I have tried manually retracting filament using the buttons and it works perfectly. It only fails during prints.

@Sublime: I am using Slic3r Version 0.9.2.

@Cefiar: I am not sure what hot end. It is the standard hot end for Wade's Extruder. 0.34mm nozzle. I can retract manually using the buttons without any issues so I doubt that would be the problem.

@Davejones: Repetier Host does not have any settings for retraction. Unless I am mistaken, all printing related settings are in Slic3r (because Slic3r is the program the generates the G-code).

Does anyone else have any more ideas as to what I could do to fix this problem?

Any help would be greatly appreciated.

Eric

Eric.

If you are using Repetier Host and the Repetier firmware then it is possible that you have the Repetier OPS (ooze prevention system) activated.
If you have repetier OPS activated and you also have retraction activated in your Slicer - you will get some very strange retraction results.

To check - in Repetier Host, 'Config' then 'Firmware EEPROM configuration'. Scroll down and look for 'OPS operation mode'. Set this to Zero to disable.

The good thing about using OPS is that you can tune your retract settings on the fly i.e while you are printing an object and get to see the results straight away. But you must have retraction disabled in your slicer to do this!

Edited 1 time(s). Last edit at 09/26/2012 08:01PM by davejones.

Thanks for the tip Dave. I tried to check what you said but when I clicked on 'Config' in Repetier Host, the button for 'Firmware EEPROM configuration' was "dark" (unclickable). I think this is because I am using Sprinter firmware instead of Repetier Firmware.

I actually realized that I accidentally said that I was using Repetier Firmware in my initial post. That was a mistake, I am sorry about that. To confirm, I am using Sprinter Firmware, with Repetier Host. So I guess the fix you suggested does not apply? (Are there similar settings for Sprinter?).

Thanks a lot for your help. Let me know if you have any other ideas.

Eric

RP Iron Man Wrote:
-------------------------------------------------------
> I am using Sprinter Firmware, with
> Repetier Host. So I guess the fix you suggested
> does not apply?

Correct

>(Are there similar settings for
> Sprinter?).

Not as far as I know - but I don't use Sprinter.

I had the same symptoms on my MakerGear Mendel Prusa kit with the brut-head extruder. Retraction didn't work, but retraction compensation worked fine, and I couldn't turn it off. So I ended up with blobs at the start of every segment.

Eventually I wondered if retraction speed was the issue. Short answer - yes it was. The default retraction speed in my slicing software was too high for my printer. The stepper motor was stalling trying to retract too fast against the pressure of the molten plastic in the hot end. Extruding is mechanically less effort than retraction.

I used Pronterface's "extrude" and "reverse" buttons, and changed the mm/minute settings down until I found a speed where retraction was reliable. Then I plugged that speed into Slic3r. No more problems. The setting will depend on your filament type, hot end design, extruder motor gearing and the temperature you are extruding at, so my figures won't be any use to you.

Hope that helps.

Andrew

BrazenArtifice Wrote:
-------------------------------------------------------
the
> pressure of the molten plastic in the hot end.
> Extruding is mechanically less effort than
> retraction.

What? It is the opposite. The pressure in the hotend is enough that it tries to turn the motor backwards which increases the max retraction speed. The pressure in the nozzle then limits extrusion speed. I am not saying speed is not the issue but rather that the retraction can be faster than the extrusion. The problem if retraction would not work while extrusion did is most likely a result of the retraction acceleration in the firmware being set much higher than the normal acceleration.

With a bowden extruder the effect is much greater and the force of the compressed filament is so great it will turn the extruder backwards if you try and extrude faster than the hotend can melt the plastic. But this means you can have the retraction acceleration turned all the way up to 10,000. For most other extruders the retraction acceleration is set to 3000 and max 10,000 in Marlin which could be your issue.

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

Thank you so much Andrew!!! You were right!

Speed was the issue. I calibrated the optimum retraction speed manually using the buttons, and then applied it to my Slic3r settings. The end result was much better, though not perfect. I still have to adjust the settings. Unfortunately, I had to lower the speed to 3 mm/s, and it is now slowing down my prints. I am going to see if I can increase the speed a bit more and maybe adjust the retraction length.

Pictures:

[www.flickr.com]
[www.flickr.com]
[www.flickr.com]

Anyway, the bulk of my problem is solved! For that I am very grateful. Thanks to Andrew and all of the other RepRap users who tried to help me with my problem.

Eric

Thanks for correcting my misunderstanding, Sublime, I'm always glad to learn something.

Checking my Marlin config file, my retract_acceleration is set to 7000 mm/s/s, compared to 2000 for normal acceleration. So you're probably right that I should reduce the retract accel and then increase the retract speed in Slic3r. I'm sure that'd improve my retraction results.

Wouldn't be the first time I've been burnt by Marlin defaults that don't work well with my Prusa.

Cheers,
Andrew

Replying to myself

Yes, just confirmed that changing my retract_acceleration from 7000 to 2000 in Marlin's configuration.h now lets me retract reliably 10 times faster than I used to be able to do. So Sublime was right that the problem was in Marlin's default retract acceleration being way too fast for my printer.

Thanks again, Sublime

Andrew