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Printing stops due to blockage after 2 hours out of 7

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I have posted this at the end of another thread but then read that it would be better to start a new thread for a new problem. So please excuse double posting....

So I have a 2 week old UM2. I have printed out 8 large gears (2 hours each) and a model of a upper end of humerus without a problem. The latter took about 7 hours to print and was/is perfect.


Then I tried to print a heel bone which was a big file 80+Mb when in stl. I reduced the size to print 50% of true size. It was meant to take 6 hours to print. I have tried repeatedly to get a complete print but the filament stops flowing after 2 hours and the print head carries on printing air. I have now done an Atomic unblock on 3 or four occasions. Each time the nozzle blocks after 2 hours or so





I have Cura set to 50mm/sec and all other settings to default


I have done the extrusion test with the print head set to 240

Here is the result



It seems that extrusion is not the problem - or is it?


This is so frustrating. I feel like sending the printer back if it is this difficult to consistently get a good print




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Assuming you've read all the other topics on feeders, Teflon insulator, general settings, etc....

Have you gone into layer view and looked at what the printer is doing in each layer? Some files I have like that bone you are trying to print are really messed up on the inside, and the printer does some really weird stuff. This has to do with some software exporting the .stl or .obj with voids on the interior. You can go into expert settings and try the different "fix" options on the bottom right of the expert menu and look at the layers, and see how they're printing.

Also, looking at your picture, you're first layer looks terrible! And those layers look like they're .35mm or something! EDIT--> Wow, that came off sounding like a douche, no insult intended :)

If I were in your shoes, and had to print that model, I would print it in .14mm~.22mm layers, I'd make sure my first layer was perfect. I'd make sure my layer view in Cura was showing a nice clean build. I'd probably open the model in Netfab and do a repair on it. I'd make sure all my settings were good, such as temps and speeds. I'd make sure my retraction settings were dialed in (usually 4.5mm ~ 5mm) by doing a retraction intensive test print (not the cylinder extrusion test).


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Your extrusion test looks okay indeed, not perfect but should be enough to get good quality at a decent speed.

Regarding your print, i would follow Solid Print 3d's advises, look on the layer view if you can spot something odd. And make sure your model is a good solid (netfabb basic will help checking this).

If everything looks good then there's a problem with either the temperature (too low) or the speed (to high) or both.

If you cleaned the nozzle with the atomic method we can rule that out.

How is your feeder doing? Do you hear some clicking? Does it miss some steps?

One more thing, for such a complex model, wouldn't it be better to cut it in half and print without overhangs? The glue back the two pieces. You would gain in speed and quality.


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I think we need to get some idea of the settings which were used for this print. E.g. print speed and temperature, and whether the feeder was grinding or skipping (making the chock sound).


I reset the settings back to default

Layer height 0.1

Shell thickness 0.8

Enable retraction

Bottom/top thickness 0.6

Fill 0%

Print speed 50mm/s

Touching build plate


Nozzle 0.4

Initial layer thickness0.3

Temperature is whatever the machine defaults to when loading new filament and selecting PLA.

Once the nozzle blocks then the feeder is grinding the filament of course

Is there a shareware program that can split a model into two equal halves

Netfab is not cheap. Is there a trial version or a shareware alternative?

What do I look for in the layer view that would be odd?

Thanks for everyone's input. Please excuse my ignorance, but I am new to 3D printing (obviously) but trying to perfect getting from CT scans of bones to reliably printed 3D models



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Actually there is no "of course" regarding grinding. The UM2 isn't supposed to grind, it is supposed to skip back instead. However sometimes it does grind, and the significance is that there is nothing you can then do except abort the print and cut off the bad piece of filament.

Perhaps you thought that grinding was some kind of generic term. It isn't. It refers to when the knurled drive on the feeder motor has ground a curved divot out of the filament. The knurled drive therefore no longer pushes the filament and the print stalls completely. It's a bad situation since the hot end can overheat - in addition to wasting filament. As I understand it the UM2 was designed with a weaker motor that the UM1, so it theory it doesn't have the power to grind, instead it will fail to turn and instead skips back to the last stable position.

So I think we do need a proper answer as to which failure more you get.


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Used Meshlab to make the model hollow and again reduced size of x,y & z to 0.5. Re-printed and it stopped and blocked at about the same point again. Back to the Atomic unblock again..........................

The last bone that I printed was a fracture of the upper humerus. the stl was (only) 14Mb. It printed fine. Maybe this heel bone model is just too big/complex with an stl of 80Mb

All very frustrating for a simple bone fixer. Happy to dropbox the stl if someone wants to play and see where I am going wrong.........




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Ok, just had a look at the models.

It appears they are the result of a kind of scan, perhaps X-ray or something alike.

The bad news is that your model contains lots of detached parts. This can be easily viewed in MeshMixer (was suggested before as an alternative to things you cannot do with netfabb for no money) by doing Analysis > Inspector (lots of magenta spheres). That's something that has to be cleaned up, though this is not your problem :)

It is also that the interior of the bones has many crazy details that for sure are not fragments of the broken bone, but just the result of scanning. It's most probably not the scanning device itself, except for the limitation of its resolution, but of the post-processing software that does not an "automatic cleaning" of any sort.

And here starts the trouble. All these nitty-gritty produce lots of retractions. Correlated with some lack of fine tuning of the printer and of the slicing parameters, I believe that your hotend is clogging. I don't know exactly how UM handles clogging once it happens, but I expect that, at least for your case, the filament will be grinded, and hence no skipping, but also no feeding.

I would recommend:

- clean the model of detached parts (Autorepair all)

- reduce complexity (as pointed out by Didier above) recursively, as many times as you cannot seize a significant distorsion ( I think you can easily get it to 200-400k triangles)

- smooth the interior of the bone as much as possible (can be done with sculpting tools of MeshMixer); this should be manual to avoid deforming things of relevance

- slice it again

- inspect the gcode layer by layer and see how simplified/complicated looks (you should be able to compare with the initial gcode)

This is all on the model side.

There might be issues though with the printer and printing parameters tuning (for instance, I don't get why do you use 0 infill).


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Many thanks for all this. Most of the other bone models that I have made have been tubular bones with little in the middle. In contrast the heel bone is quite solid. I think that is the basic problem. I will try to get another heel bone scan and see if the same thing occurs. If it does, I will have proved a limitation in getting from CT scan to 3D model

I will also try and follow you advice and see how I get on

Many thanks for your time



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Well, is not only with CT. It's scanning in general.

The scanner itself is helpless, except if it is accompanied by a good post-processing application.

This has to intelligently smooth the model, clean it up and do some other stuff for the model to become useful for other application.

This is however application dependent, since different application will have different requirements.

I don't know the requirements for the output generated by the software used with the CT, but it definitely not appropriate for direct 3D printing.

http://umforum.ultimaker.com/index.php?/gallery/album/1439-medicalmodeller-bone-printing-issue/ are some images underlying what I wrote in my previous post.


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Hello MedicalModeller - I think I got the exactly same problem ..... And I am frustrated already. I went trough hours of troubleshoot, reassembling my printer (teflon thingy is unharmed), several atomic cleanings and whatnot. Even the ColorFabb support which was very patient and enthusiastic couldn't help me.

I just filed an official support request at Ultimaker - I will keep You updated should I ever manage to solve the problem. You can PM me if You want for further info.


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