Latest and Greatest Techniques to Counter Retraction-related Strings

[mifga 0]

Hey folks!

I've been studying posts about strings and retraction heading back to 2010 on here and wanted to put up a quick request for how Ultimaker users are tackling this, particularly with the assembled machines in their most recent configuration.

Reason I bring this up -- I was printing BEAUTIFUL prints on an assembled ultimaker in PLA silver the other day and noticed that i was seeing more wispy strings than when printing the same model on the printers I already had (Rep1/Rep2 in particular). The particular model I focused on is the same one I read about here printed by flouSH last summer, the Lightbulb:

http://umforum.ultimaker.com/index.php?/topic/467-post-your-latest-print/page-5

Here's the model: http://www.thingiverse.com/thing:22851

This is something of a stunt print that people typically print to see how 3D printers can tackle registration and retraction. I noticed that I seemed to be getting worse strings than expected and was seeing some of them touching up against the rising towers and messing with layers.

I read about solutions such as the shims to help prevent the play that reduces the effect of retraction somewhat, but I was wondering if there are other routes or retraction values that most of you use to counter this sort of thing these days.

For the most part, I don't care about strings when the parts are pristine. I have a cheapo hot air reworking station I can use to quickly heatup and soften back any marks after I trim them away. But I could see friends I showed the light bulb to shaking their head and tisking when considered against other extruder models that have retraction more mechanically accurate to the slicing.

And wow, I printed a calibration cube at one point when checking the machine out that was so beautiful I though the machine had substituted my print with an injection molded piece....

 

[illuminarti 18]

Hi! Welcome to the forum.

There are a few things that you can tweak to get better retraction.

The first thing is to make sure you actually have retraction enabled. In Cura, there's a separate check box to turn on retraction, on the first tab, separate from the retraction speed and distance settings on the second tab. Sometimes that checkbox gets overlooked.

Then you should get an updated firmware that fixes the retraction speed bug. Without that, it's hard to make controlled adjustments to retraction. The latest source code has had the fix for about 6 months now, but it hasn't made it into the released version that comes with Cura. So you'll need to build your own firmware. See here for a tool to help build Marlin, if you're not familiar with doing that.

Once you have fixed firmware, you'll want to experiment with retraction speeds in the 25-35 range. I think most people use a distance of 4.5mm.

Putting a shim on the cold end of the Bowden tube will help keep the Bowden length constant, and so give more reliable retraction too. I quite like this one.

Then you will want to look at adjusting the temperature of your filament. Different brands and colors will behave differently - but usually, lower temps are going to reduce the amount of stringing.

Finally, increasing your travel speed will help reduce stringing. The faster you move between section of print, the more likely you are to snap the bead of filament and not stretch it out, and the less time there is for the head to ooze.

With a little care it's quite possible to eliminate pretty much all stringing on prints.

 

[mifga 0]

This was tremendously helpful, thanks! Actually, kinda wow -- this totally covers that bases and I wish I had asked this question last week.

Yeah, I definitely should have taken the time to rebuild Marlin like you suggested. I had retraction flagged as true, but i'm kicking myself that I resisted building latest dev things while experimenting. looks like I just missed reading the real goods I should have read.

 

[gr5 2,177]

I have the same clip that Illuminarti refers to which requires a wire tie. The other ones all eventually broke.

I have found that some PLA will string (a little) no matter what you do but other's are very well behaved if you print cool enough:

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

 

[3dcase 37]

Hi,

A retraction related question (I guess) .

Spend a few cups of coffee reading Q&A on these forums. But found no answer yet for my question.

Using Cura 13.06.4, (in 13.04 no problems, but I start using 13.06 more often, because its moving around a lot smarter and faster (I think :cool: ))

While printing a vase or other solid object, retraction enabled, no infill to hollow the object, 0.8 wall thickness.

retraction is working, feeder is running backwards sometimes. Accept when the printhead is crossing the print from wall to wall. in cura seen as a straight blue line.

Is there a solution to get rid of the stringing, (temp is as low as possible, travelspeed as high as I want it)

I read a lot of marlin troubles and updates. about, what I think, was related to speed.

Is it a cura problem, or a marlin thing?

Regards kees

 

[illuminarti 18]

This is just the way the current version of Cura works. 13.05 onwards use a totally new backend slicing system, and currently it does two things that mess up vase-like prints where you are only printing the outer shell of an object, and have zero infill.

Firstly it adds extra infill in spots to thicken overhanging parts. This is ok on the inside of closed objects, but looks bad on open shapes. Secondly when moving around within the shape to print that extra infill, it doesn't retract.

I think the only solution at the moment is to use 13.04. That also allows you to use the Joris feature to get a continuous spiral (provided your wall is only one pass thick).

 

[3dcase 37]

thanks for the answer.

that leaves us waiting for a cura update, and switching between 13.04 / 13.06 I guess.