Jump to content
Ultimaker Community of 3D Printing Experts
Sign in to follow this  
Nicolinux

Blob and Mess - UM2

Recommended Posts

Hi,

I found this odd behaviour when starting a print and the first thing that gets extruded is a big blob of plastic. After that the print fails (almost always) because there isn't enough filament comming out of the nozzle. And the little filament that comes out does catch the nozzle and the whole mess gets dragged around and prevents a clean first layer. Obviously this is an issue with small(ish) objects because there is not enough time for the filament flow to stabilize. But you know, I demand the UM2 to be perfect for small and big objects :)

The first time I posted about it (including a video) was here (http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/?p=42399). Illuminarti hints at a firmware bug (http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/?p=46653).

I wanted to document this issue because it is annoying and because I guess it happens to other people too. It would be interesting to see if it is only restricted to the UM2 (if not, I'll edit the title).

Here is a picture of the mess:

blob mess

 

I know how to avoid it - moving material (menu -> maintenance -> advanced -> move material), but that's not a real solution, just a hack.

The usual workflow with this issue is like this:

 

  1. Start print, see the blob, hear the extruder skip once
  2. Swear and abort print
  3. Remove the mess from the bed
  4. Start the print again -> works (never had two blobs in a row)

So, hands up. Who had this issue before and wants to kick it (the issue) in the nuts? :angry:

 

Share this post


Link to post
Share on other sites

Well I am not sure if this will help.

I have had similar issues after aborting prints then instantly starting a new print. I think when I abort the retraction is so long it does not fill the nozzle for the next print properly. And cannot push material out in time and the remaining plastic begins to blob and come out from gravity with the heat. Eventually the material catches up and it prints as usual but it has a negative effect on the first layer :(

Going into advance setting and advancing the material until it moves out of the nozzle to ensure the nozzle is properly filled. Then go and print.

Maybe this helps maybe it doesn't.

Cheers,

Share this post


Link to post
Share on other sites

Hi Cleven,

Sadly it doesn't. For me this issue happens when I start a new print after where the previous print was successful. And before the blob occurs, the nozzle oozes quite a bit while moving to the start location - as with any print. I know that moving material fixes it, but this issue is random and I would like to print without having to always move material before starting a print.

 

Share this post


Link to post
Share on other sites

Hi Nicolinux

I have the same situation as you, i can not just start a print and it works, so i don't even bother these days i do the following work flow straight off now as it just pisses me off the normal way..

1) manual heat up build plate

2) while waiting for the build plate then manual move material until i get a nice flow then reverse a couple of blips.

3) return to main menu and then start the print...

Just as a side note i have got my massive under extrusion back after 3 months of fitting a new Teflon....

 

Share this post


Link to post
Share on other sites

Nico. It was happening to me too. But I think for different reasons I had a few things which were all causing the same issue. I have not had the issue in a while. I will post my solution other issue for you and or others below.

When I had the issue I also reinstalled the firmware. But I doubt this had an effect. Including the last post about aborting the second part is below.

Blobbing lack of extrusion

The filament was crushed /worn down in the feeder which was getting slightly jammed in the tubing. Inspect filament for worn or flattened areas.

1. Remove damaged filament section

2. Make sure the extruder is not biting into the filament too hard or too lightly.

3. If that doesn't work reduce retraction length. The constant back and forward motion can flatten the filament.

4. Increasing temperature can fix the viscosity allowing for less force on the filament during extrusion.

Maybe this helps someone with a similar issue.

Share this post


Link to post
Share on other sites

Thanks Cleven,

I'll take a look at the filament when a blob occurs again. Right now I have the suspicion that it happens when I start another print before the printer cooled down. Will keep an eye on this too.

 

Share this post


Link to post
Share on other sites

I usually manually heat the bed and extruder using Pronterface, then before starting the print I extrude a few mm until I see plastic start to come out.

Then I start the print, and use tweezers to remove the excess plastic just before the UM2 starts printing the skirt.

Also, having a large skirt or more than one loop helps clear the extruder before it starts the piece.

 

Share this post


Link to post
Share on other sites

this is my workflow also, heat up the build plate, manually move material to ensure it's flowing nicely, then hit print.

Happy to say I've had good consistent printing for a while now, I just ran a 24 hour print with no under extrusion.

 

 

Hi Nicolinux

I have the same situation as you, i can not just start a print and it works, so i don't even bother these days i do the following work flow straight off now as it just pisses me off the normal way..

1) manual heat up build plate

2) while waiting for the build plate then manual move material until i get a nice flow then reverse a couple of blips.

3) return to main menu and then start the print...

Just as a side note i have got my massive under extrusion back after 3 months of fitting a new Teflon....

 

Share this post


Link to post
Share on other sites

Hey guys,

I think I am onto something here. The blob seems to always occur when the UM did not have time to cool down from a previous print. Since the heated bed takes a bit to heat up, I often (carefully) remove finished prints from the still hot heated bed. Then I start another print. And that's where the blob comes. Maybe there is a connection between hotend temperature and the pressure inside the nozzle.

 

Share this post


Link to post
Share on other sites

EVERY time, before I start a print, I always extrude at least 30mm, ie I want to see 30mm of perfect extrusion before starting. Some filaments can go quite gloopy if left in the head for even a short time at print temperature.

 

Share this post


Link to post
Share on other sites

When I was putting together the gcode for the new extrusion test last night, I noticed that Cura generates gcode that starts with a G11 - deretract - at the start of a print.

The firmware handles that by first checking if it thinks that it is in a retracted state already. If not, it gets ignored.

I think that what is causing the blob is that when doing prints in series, sometimes the printer ends up thinking that it has retracted (e.g., at the end of the last print). And then during the print start up, the head gets reprimed, so that when the head moves to start printing the skirt, the initial G11 gets read and, mistakenly, actually fires. As a result the printer tries to extrude several mm of filament in a sudden jolt out of a full print head, causing the blob.

As to exactly why it's happening, I'm not sure - it could indeed be something to do with the cooldown sequence not completing nicely... but whatever the root cause is, I'm pretty sure this is what's crating the blob that Nicolinux highlighted. It's an unwanted de-retract on an already full head.

 

Share this post


Link to post
Share on other sites

EVERY time, before I start a print, I always extrude at least 30mm, ie I want to see 30mm of perfect extrusion before starting. Some filaments can go quite gloopy if left in the head for even a short time at print temperature.

 

Then you aren't going to like 14.04RC - it keeps the head in the Home corner instead of moving it to the front before raising the bed, so you no longer have a chance to remove that pre-loaded excess extruded thread before printing starts.

This is a real issue for PLA, as the stuff turns brown and eventually carbonizes if you leave the heat on between prints. Flushing out a couple of cm before printing can avoid a lot of clogs and restarts.

 

Share this post


Link to post
Share on other sites

Then you aren't going to like 14.04RC...

Sorry - bad explanation. It moves to the left-front corner of the volume as before, but then waits until the bed is nearly all the way up before it extrudes the blob, which it drops on top of the left clip, and gives almost no time to remove the excess before printing begins.

 

Share this post


Link to post
Share on other sites

There is no 'start gcode' for the UM2 - the print start and end sequences are hard-coded in firmware.

 

Well I am no super expert on the subject but I am sure you can fix that with appropriate code in the Gcode start section, unless I am missing a point there. Mind you that does seem to be unnecessary work to do.

 

Share this post


Link to post
Share on other sites

Eldrick, that is the way Slic3r works and although I now use Cura I probably prefer the Slic3r way. If you have a skirt or a brim I have always found it easy enough to remove any pre-print filament. If you do not then a skirt is a good idea as it helps get the extruder pressure equalised before starting the print proper.

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Our picks

    • Introducing Ultimaker Cura 3.6 | Beta
      Ultimaker Cura 3.6 | Beta is available. It comes with new features, bug fixes, and UX improvements. We would really like to have your feedback on it to make our stable release as good as it can be. As always, you can download the beta for free from our website, for Windows, MacOS, and Linux.
        • Like
      • 92 replies
    • Print Core CC | Red for Ruby
      Q: For some users, abrasive materials may be a new subject matter. Can you explain what it is that makes a material abrasive when you are not sure which print core to use?
      A: Materials which are hard in a solid piece (like metals, ceramics and carbon fibers) will generally also wear down the nozzle. In general one should assume...
        • Like
      • 30 replies
    • "Back To The Future" using Generative Design & Investment Casting
      Designing for light-weight parts is becoming more important, and I’m a firm believer in the need to produce lighter weight, less over-engineered parts for the future. This is for sustainability reasons because we need to be using less raw materials and, in things like transportation, it impacts the energy usage of the product during it’s service life.
        • Like
      • 12 replies
×

Important Information

Welcome to the Ultimaker Community of 3D printing experts. Visit the following links to read more about our Terms of Use or our Privacy Policy. Thank you!