PLA and Retraction on Replicator / Mk8

[Martin Galese]

All,

I've been trying to dial in my PLA printing profiles on the Replicator, but I'm struggling to get retraction working without causing repeated PLA jams.  Without retraction, I have no problems printing with PLA.  With retraction, at almost any settings / temperature, the filament seems to go to hell and get jammed early to midway through the print.  Have other people had good luck printing in PLA with retraction?  If so, with what settings?

Thanks,

--
Martin Galese

[Dan Newman]

Are you using extruder temps below 200C? If not, then try 195C. PLA
has a lower working temperature. If you run with your extruder at
closer to ABS temps, then there is a very common problem with the
heat travelling up the filament and softening it ahead of the pinch gear
and causing printing failure mid print. With retraction you are
adding to the problem: backing some the softened filament back into
the pinch gear.

So, lower extruder temps. Maybe even try 185 or 180 if you haven't.
And if that doesn't work, then sounds like you need less aggressive
retraction settings as well.

Dan

[PropellerScience]

On Jul 13, 8:39 am, Martin Galese <mar...@galese.net> wrote:
> All,

>  Without retraction, I have no problems printing with PLA.

I don't understand why you would want to change something you have no
problem with?

[Herón Ordóñez Guillén]

PLA oozes more than ABS, without retraction the strings are terrible in my experience.

I use 1mm retraction at 40mm/s on a MK6+ and it gets rid of strings, but I'm using 3mm filament now.

Maybe try with something that extracts roughly the same flow? like 3mm @ 120mm/s ? is that too aggresive on the MK8?

I'd try lower temperatures too. And I can't recommend active cooling enough. But I wouldn't know how to implement that on a MK8

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[Gerald Orban]

Hi Martin,

I've just recently started printing PLA with my replicator and after some fiddling here's what I've found works best:

- Nozzle Temp: 170C (I can probably get to 160 and have it print fine, haven't had time to experiment)

- Retraction Distance: 0.5mm (no extra retraction)

- Retraction speed: 80mm/s

- Bed Temperature: 60C

- Feed rate: 60mm/s

- Travel rate: 150mm/s

With these settings stringing rarely happens, and when it does it is barely noticeable. I'm still improving on this profile but it should give you a good place to start!

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[Cymon]

THank you so much for these settings. I've been terrified of making the switch PLA. I'm still hesitate because I've got this back stock and mixing and matching isn't something I want to deal with. But it's just so... good. These settings are a start.

[Aljosa]

One of my biggest goals with the Replicator profile was to eliminate the need for separate profiles for ABS and PLA, this was something that a lot of work went into. Previous practices and old information floating out there would lead you to believe you need to change a whole bunch of settings in order to switch to PLA. That's simply not true anymore, you can literally just switch plastics and when printing with PLA turn your bed temperature off for smaller things or to around 40-50C for larger prints.

Id really love to hear why people are lowering the temperatures and fiddling with retraction because these are two settings that can dramatically effect your print in a negative way. Printing at temperatures bellow 200C puts a lot of stress on the filament at normal speeds. If your printing in clear PLA its really easy to tell this is happening by looking at your extrusion. When clear PLA is under stress it becomes very cloudy and foggy, when its at a more optimal temperature it comes out looks very clear, and almost glass like.

The recent profile in RepG27 has some revised retraction settings to correct an issue with thin features. Cranking retraction up is again another thing that can cause your prints to come out bad or just outright fail. Really what you want to go with is the absolute minimum in distance and speed you can possibly get away with. When your printing something that makes the extruder do several reversals in a very short time frame having your reversal settings at high numbers can cause the filament to strip as it gets forced past the drive gear over and over again, this is true for any time of extruder the plastic will simply wear down after a certain point.

For people that are changing temperatures is this based of what you have read online or do you guys have other reasons to do so. I'm very curious to collect more data on this because the simplicity of getting a print going is something I'm constantly working on, and its something I think we did pretty well with Replicator. Id like to make it as simple as possible to print regardless of whether your printing in PLA or ABS, juggling a trillion profiles is not something I think I user should have to do in order to get there desired object.

[Martin Galese]

Thanks for the comments all,

Aljosa, for my part the default settings work for awhile in PLA, then jam badly.  That's the pattern on literally every setting that I've tried (including Gerald's) that involves retraction. Turning off retraction instantly leads to successful multihour prints, at the same settings that I'd otherwise use for ABS -- as you hoped for.  On most objects, though, the strings are beyond bad.

I've been using 1.75 Silver PLA from ProtoParadigm, but it's happened with clear PLA from Makerbot as well.  I've also been using a small household fan to cool the build area as the PLA is extruded, to improve definition.  As for the failure mode, I've taken fan and heatsink off for short periods to watch the extrusion and see what the issue is.  So far as I can tell, it is not that the filament is slipping against the drive gear, or that the gear is otherwise tearing out a divot.  Instead, it appears that the filament is building into some sort of clog below the gear.  When I extract it after a failed print, I see normal filament, normal filament with gear marks on it, thinner filament that looks stretched, then a short, fat part of filament that is wider than the rest.  When this happens, I can usually clear the clog by heating the nozzle up to working temperatures and backing the filament out -- but not always.

I'm really at my wits end with PLA, which is a shame because I like many aspects of it better than ABS.  But I am printing nearly perfect items in ABS, often at 100 mm/s, without any strings.

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[Gerald Orban]

I've been messing with these settings specifically to improve print quality. The reason being that I was anything but impressed with the print quality of the default Replicator skeinforge profile (ever since I received it in March/April). I found that the main culprit was the negative extra retraction (which has since been removed iirc) and everything else has been trial and error.

I decided to up the retraction speed because I found that sections of the perimeter would not be printed (specifically from where the head starts drawing the perimeter after travelling from the interior) at all unless I upped the retraction speed. This held true for both ABS and PLA, I found and was a suggestion from someone on this group.

As for the temperature reduction from ABS, it is true that the printer WILL print PLA at that temperature (220C to 240C), however, at that temperature I've found that blobbing and oozing is completely unacceptable. Lowering the temperature helps to keep the PLA from oozing out and I'm hoping to improve the settings at some point to make dualstrusion work correctly: without blobs of the other colour permeating the print. The temperature change came as a suggestion by some extremely helpful folks from both the Reprapper forums and the local Vancouver printer owners group.

I totally respect that you're trying to simplify the settings to make the switch between PLA and ABS as painless as possible, especially with a single profile for both (for everyone's sake!) and hope this answers your questions.

[Shawn]

a comment from the peanut gallery... Did you select PLA in the SF
profile? Or are you applying the default ABS settings to PLA? (I've
yet to work with PLA, so want to know what steps to be aware of when I
do...)

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[Gerald Orban]

I didn't even switch the profile from ABS to PLA. Using the vanilla ABS profile with the modifications I noted above. In fact the only difference between my PLA and ABS profile are the temperatures.

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[Aljosa]

Gerald

Can you elaborate a bit more on what was wrong with the print quality, I have to say "anything but impressed" is a first for me, and I have a feeling there is something else going on with your bot and not the profile. I'm probably one of the most if not the most anal people you will encounter when it comes to print quality, and making the absolute best print you can. Getting user specific input in key areas is important to me. This is especially true when it comes from users that print a lot. The current as of RepG 37 profile has changes slightly but the major part was retraction, specifically what you pointed out. 

Do you have a single or dual head setup? What firmware are you currently running? Id really love to hear in a bit more detail what you saw as a problems, and in what areas.

[Gerald Orban]

I have a dual extruder Makerbot Replicator running 5.4 FW and RepG37 and am equally anal about print quality :)

I didn't get any photos of the issues but I found that a lot of the perimeter was still missing similar to a photo I posted a while ago in this thread:  https://groups.google.com/forum/?fromgroups#!searchin/makerbot/gerald/makerbot/teNOXdivuCM/XB_0oyWhWV4J. The print completed (unlike the clogged nozzle issue in the linked thread) however, there were significant stretches of the perimeter missing.

The missing perimeter issues seemed to get worse using the default profile as increased the feed rate to 80mm/ using acceleration. I haven't upgraded to 5.5 yet as my HBP's connector had turned dark brown due to the HBP wiring issue (which has been discussed on these forums) and have been afraid to even power it on since. A replacement wire harness is in the mail and I should receive it shortly. 

There were some other issues with the accuracy of the print (rounded, smoothed out fine details which is expected at high feed rates) at higher speeds when I first installed the 5.4 firmware however, I wasn't able to narrow down the cause. Reducing the print speed to 60mm/s brought back enough accuracy along with raising the nozzle temp to 240C (for ABS) along with ensuring the machine was properly lubricated. I'm not convinced this is a problem so much as the expected behaviour when increasing print speeds.

I'm willing to give the default profile a try again, but it will have to wait until I get the replacement part.

My major disappoint above all else so far has been with dualstrusion. Looking at the demonstrations in CES they were near perfect (from what I could tell) with no drops of the other colour intermixed with the currently printing colour and have yet to replicate those kinds of results with any Skeinforge profile.

All in all, I'm looking forward to getting back up and running when the new wire harness arrives!