Retraction is leaving "hangers" between posts

[jimtiffinjr 0]

Greetings everyone,

Hoping someone can help me out with this retraction problem... at least I think it is a retration problem. :-)

As you can see from the picture below, there is a "hanger" of PLA left on each post where the filament retracts so the nozzle can travel to the next post and begin extruding again:

 

I usually just cut these off, but I'm wondering if I should be even getting them in the first place.

 

I'm hoping another Ultimaker user can tell me if these "hangers" are something that is supposed to be there, and then just removed after the print. Or if there is something wrong in the print settings that I am using. Should it be the latter case, I've included some details that might give others some insight into my problem

 

• Retraction is enabled
  
• Retraction speed is 40 mm/s
  
• Retraction distance is 4.5 mm
  
• I've installed this Extruder Multiclip to help with retraction
  
  • The problem is still occuring
    

   

  [*]I'm using 3.0 mm white PLA

   

  • The problem occurs regardless of the color
    

   

  [*]Print speed is 50 mm/s

  [*]Print temp is 220C

  [*]Layer height is 0.1 mm

  [*]Flow rate is 100%

  [*]Travel speed is 150 mm/s

  [*]Infill speed is set to match print speed

   

Thoughts?

 

[IRobertI 521]

You say retraction is enabled but is it actually happening?

 

[gr5 2,268]

1) Make sure it really is retracting by watching the extruder.

2) Lower the temperature. Much more information here including photos of your "hangers" which I call "strings".

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

 

[jimtiffinjr 0]

The retraction is definitely happening as I see the large gear in the back reversing direction and the Bowden tube moving as the filament suddenly changes direction.

Thank you gr5 for the link to the photos of the calibration tests. The "strings" on the right-most tower of the stringing test with 100% are exactly what my "hangers" look like. I'll reprint the same structure tomorrow and adjust the temperature at different heights to try and dial in what works best.

I'll keep the speed consistent for the experiment.

(But looking at some of the speeds shown in the labels of your images, that might be something worth exploring in some other experiments. That's one variable I haven't explored much on my printer. The default has been pretty much where it stays.)

Stay tuned for some pics!

 

[3dmaker4u 0]

My experience with white PLA (sourced from RepRapWorld) is it oozes more than other colors at the same temperature. So it requires lowering the temperature. As a consequence it might be that the printing speed has to be lowered as well.

However, I don't think this is the main, or at least the only, reason for the "effect" you get.

What do you mean by "the Bowden tube moving"? Is it just shaking due to reversal, or it moves back and forth together with the filament. The later shall not happen, or else the tube is not... Bowden. I mean for it to properly function, it is mandatory to be well fixed at both ends. Any play will reduce the efficiency and precision.

 

[gr5 2,268]

I've also had much worse trouble with hangers or strings on my white PLA. White PLA is tackier/stickier and no matter how low I go with the temperature I get these things. Most other colors aren't so bad.

 

[jimtiffinjr 0]

What do you mean by "the Bowden tube moving"? Is it just shaking due to reversal, or it moves back and forth together with the filament.

 

It is the former. As the filament changes direction, the tube flexes slightly. It is fixed in position at both ends.

I seem to be getting this problem with other colors too, but as you've explain, it is most likely a temperature related issue. I will run my experiment with different temperatures using the white PLA and see if it improves. Even if it doesn't come out perfect, I'll know what adjustments to make with those other colors.

 

[jimtiffinjr 0]

I've done some more prints and had a little improvement in terms of stringing, but eventually ran into underextrusion problems. The pics below show the results at different temps.

220 Degrees

 

210 Degrees

 

200 Degrees - with small bits of underextrusion right at the base of the posts...

 

190 Degrees - which is where the underextrusion gets really bad...

 

And then back up to 195 Degrees - where the underextrusion (and some structural integrity :smile: ) issues still occur

 

So my new theory is that the speed of the print now needs to come into play. I'm thinking that 205 is a good temp, but wondering if I should go with more speed or less speed. I'm currently printing at 50mm/s, but since the temp is lower I think I should go slower. This might also give things more time to cool.

 

Or is my thinking on this backwards, and I really need to consider faster speeds.

 

Thoughts?

 

[gr5 2,268]

Slower. The extruder is not powerful enough to go any faster at such a cold temperature. And if it was, the filament would grind up. The extruder can only push with about 10kg of force (which is a lot!). That translates to about 2000psi in the nozzle. When you get down to 205C the filament is more like toothpaste than like honey.

Go to post #2 here to see more about what temperatures and print speeds work:

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

I should warn you that I found that white pla was a problem for me and I found I could not get rid of the hangers at any temperature. Whereas most other PLA's were fine. Also you might want to increase your retraction a tiny bit - maybe to 5.0mm?

I hope you have fan at 100% as that helps also.

Also if the temperature hits 170C even for an instant I believe the extruder shuts down. So I recommend you keep the temp no lower than 180C. Did you know you can change the temp *while* you print? You don't have to start over each time.

If you have ulticontroller you can use the tune menu. If you use cura, it's right there on the print window.

 

[IRobertI 521]

You might also want to consider raising your travel speed. I think the default is 150 in cura but you can increase that to 200 at the very least. A snappier move between islands can help break the filament.

 

[jimtiffinjr 0]

Thanks gr5 and IRobertI for your continued help with this.

I'm glad to hear my suspicions about going slower were correct. It was that very post that I was using as my basis for the "slow it down" theory.

The fan is running at 100%. I will use the other suggestions on travel speed and retraction and see how close I can get, understanding that it may just be the chemical nature of the white PLA.

Thanks again you two, and I'll see if I can't get another image posted at the start of next week

PS Thanks for the tip about the "changing of temps on the fly". I did know that you could do that, but being a teacher with students, it was simply easier to set up the print at the start of class and let it complete it while we worked. But keep sending other tops tips and hints!

 

[LePaul 354]

I found, thanks to the assistance of GR5, that setting the print speed down to 30-40 area, most of my problems go away. I print mostly at 220-230 since the printer is in the basement...but I printed a part that had some stringers yesterday, so I think it may be time to lower the temp some too. Off to try 210!