retraction settings with PLA

So after a few months of ABS printing I decided to try mastering PLA as well. I made myself a small fan mount for a 40mm fan and gave it a go:


(Image is a bit blurry because I took the photo while printing. I am going to change the design of the fan mount so that I have a cooling stream of air from the back side as well).


The one thing I can't get going are the retraction settings. With ABS, having 1,5mm retraction length at 40 mm/s yielded perfect results. With PLA, I tried everything between 0,5 and 4mm in 0,5mm steps (direct extruder setup). I also tried with different retraction speeds, between 40 and 90 mm/s. However, there was virtually no difference in the final result:



I lowered the extrusion temperature significantly. I am currently printing at 175 deg. C, even though the filament manufacturer suggests 190-210 deg.

Could anyone with more experience printing PLA suggest how to improve that terrible oozing?

Thank you!

Edited 1 time(s). Last edit at 06/05/2016 12:31PM by icefire.

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

Hi icefire

Couple things
With direct extruder try to avoid to much retraction, the big numbers quoted all the time are for Bowden setups, you only need enough to remove the pressure.
Careful of both the retraction speed and acceleration settings as both cab cause skipping and less retraction than you think you are getting.

I to have been a long term ABS person and have only just tried PLA, with nearly 3kg run through have really started to get a good handle on the settings for my printer.

The lesson is that often the settings are unique to you,

Missing info from the post, extruder hot end and nozzle size

Btw, I print PLA against the rules, I'm at the hot end of 207 and no layer cooling fan and get nearly zero blobs or strings

Photos not working.

With your E3DV6, don't use more than 2mm retraction or it can jam.

I print Monoprice.com PLA through a genuine E3DV6 fed by a Makergear geared stepper at 190C & 65C bed with 1mm retract @30mm/s and only get a few very fine strings. I'm using Slic3r 1.30-dev.

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aussiephil
Missing info from the post, extruder hot end and nozzle size

Genuine e3d V6, nozzle size 0,3mm

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stephenrc
Photos not working.

Fixed them, thanks

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stephenrc
With your E3DV6, don't use more than 2mm retraction or it can jam.

I have upgraded the e3d cooling and bigger retraction is no problem. However, I just tried higher retraction rates more or less out of desperation. With ABS, I have 1,5mm retraction and it works perfectly. With PLA, I started at 0,5mm but regardless of the retraction length the result is always lots of fine strings.

So, to summarize, I have tried various retraction settings and different speeds and accelerations but there is no significant difference. I am clearly missing something because I do not have such a problem with ABS.

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

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stephenrc
With your E3DV6, don't use more than 2mm retraction or it can jam.

If you have a long Bowden tube, you may need a lot more. I use 8mm retraction on my delta with 650mm Bowden tube. Any less and I get blobs at the start of travel moves. The actual retraction of the filament when it reaches the E3D is probably more like 2mm. But I see that you have a non-Bowden extruder, so this isn't relevant to you.

In my experience, stringing with PLA is caused by printing at too high a temperature. Are you sure that your thermistor specification is correctly set in the firmware? Perhaps the hot end is hotter than you think.

Edited 3 time(s). Last edit at 06/05/2016 12:49PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

This is correct. A few months ago I had a bowden setup and had 4,5 mm retraction. But now the question is how to get rid of the nasty strings.

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

Stringing depends a lot on both your nozzle diameter and the nozzle orifice length. The diameter you can usually get a handle on but the orifice length is more difficult to measure. For example, I believe MK7 nozzles have a longer orifice length than the MK8 which will give you less dribbling but higher extrusion forces. Same thing with the nozzle diameter - smaller gives you less dribbling but higher extrusion forces.

I've got a Makergear M2 with a 0.35mm nozzle (don't know the orifice length), and I print PLA at 230c with a 1mm retraction. (I also replaced the stock fan with a ducted blower.) I get very little stringing. One advantage of printing at higher temps is that the extrusion forces are lower and there is less pressure inside the hot end to relieve with your retractions.

Edited 1 time(s). Last edit at 06/05/2016 02:07PM by LoboCNC.

Never seen stringing like that with pla - do you have more than 1 roll to try?

Nope. It is my first and for now only roll of PLA...

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

In case anyone is wondering - problem solved. Tried a different roll of PLA from a different supplier.

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

That's good to know. Makes you wonder what was in that first roll!