PLA stops coming out 1/2 way through the print of a fractured bone

[medicalmodeller 5]

I have been successfully printing out models of fractured bones that I have converted from CT scans.

I now have a model of a fracture that I need to print out to help with decision making. The model is quite big when full size in spite of selecting as small a region as possible. The stl file is 16Mb. The print is meant to take about 6 hours

I have tried printing three times now. On each occasion the print seems to go fine for about 1/3 of the print time and then the PLA stops coming out the nozzle and the print head is following its path in mid air. The filament seems to be simple shuttling forwards and back rather than advancing.

I did a material change and the PLA comes out the nozzle and so seems not to be blocked

I have looked at the model with xray in Cura and there are no red lines

Can anyone help me understand what has gone amiss?

I would be ever so grateful if someone could look at the stl file and see if it works for them? I can put it into a dropbox

This is quite important for me as I need to make a clinical decision based on the model - once I get the wretched thing to print

Many thanks

MedicalModeller

 

[kris 29]

Did the feeder grind into the filament? This would prevent it from moving the material to the extruder. I have no idea what your model looks like, but I am guessing there is a lot of retraction involved. Have you tried printing slower? I print PLA only on a dedicated UM2, anything above 50mm/s and 0.1mm layer thickness is critical. If tolerances are not critical I raise the temperature to 240C which will make the PLA flow much easier. ABS is a different story

[medicalmodeller 5]

There is not the grinding as I have had when the print loosens and then the accumulation of PLA around the nozzle blocks it completely. It seems to be stuck retracting and advancing

I am using the "standard" settings of 50mm/s and 0.1mm layer

I will try heating the nozzle to 240C

Thanks

 

[chrisr 18]

Have you ever changed the hot end Isolator in your UM2? That's a part which over time, will eventually degrade and will require replacing. It will cause printing problems if it's become worn.

Have you tried the Atomic method to clean out your nozzle?

240C for PLA is very hot at 50mm/s and 0.1mm layer height. Check your isolator. :-)

 

[medicalmodeller 5]

I have not changed any part of the UM2. I have had it for a few months

I have cleaned the nozzle with the Atomic method many times when I was having adhesion problems and the PLA accumulated around the nozzle leading to a block

MM

 

[xeno 108]

It could be that at a certain height of the print, the retraction is more intense and causes the filament to grind,

or also there is a bit too much force on the filament feeder, that deforms the PLA and make it tougher to be pushed through the bowden tube.

try to cut the a section where it goes wrong from the model, and try to print it as a separate piece, so you wont have to test with the complete print again

I also have problems with retraction becoming too much for the filament at a certain point during the print.

 

[chrisr 18]

I have not changed any part of the UM2. I have had it for a few months

I have cleaned the nozzle with the Atomic method many times when I was having adhesion problems and the PLA accumulated around the nozzle leading to a block

MM

 

If you've thoroughly checked and are happy that your feeder works okay & your filament (2.85mm) isn't being tangled on it's route - which is friction free, the bowden tube is clear & your nozzle is clear... there's little left mechanically that can cause a problem.

Sorry to bang on - but you've not checked your isolator have you? You're certain that's ok then?

The isolator will deform over time and cause you problems. Replace it & I'd put money on that solving your problem. 50p bet? :smile: (I win either way)

 

[medicalmodeller 5]

If you've thoroughly checked and are happy that your feeder works okay & your filament (2.85mm) isn't being tangled on it's route - which is friction free, the bowden tube is clear & your nozzle is clear... there's little left mechanically that can cause a problem.

Sorry to bang on - but you've not checked your isolator have you? You're certain that's ok then?

The isolator will deform over time and cause you problems. Replace it & I'd put money on that solving your problem. 50p bet? :smile: (I win either way)

 

Having received the UM2 pre-built, I am not familiar with the parts. I assume that the build instructions are online so that I can work out what the isolator is. What should I look for? Is it easy to change?

MM

 

[chrisr 18]

Yes, it's straightforward to do.

These are the steps to remove the nozzle - obviously you may not need to go that far, but handy to know about all the same. The dissasembly shows how to get at the isolator.

 

You may need to order a replacement from UM (it's in their shop) or, if your UM is under warranty they may even send you another.

https://ultimaker.com/en/products/spare-parts

Phoning is the quickest way to get in touch rather than through email.

https://ultimaker.com/en/support

Assembly manual

https://github.com/Ultimaker/Ultimaker2/blob/master/um2%20assembly%20manual%20V1.1%20_english.pdf

 

[medicalmodeller 5]

Thanks for the info.

Before going down this route, would you be able to help me by printing out the file and see if it works for you on your machine?

I could share it with by drop box as it is quite big. I would not want to put the link onto the forum as this is a fracture of a real patient!

If you are agreeable, can you send me your email via a private message?

Thanks

MM

 

[medicalmodeller 5]

If you've thoroughly checked and are happy that your feeder works okay & your filament (2.85mm) isn't being tangled on it's route - which is friction free, the bowden tube is clear & your nozzle is clear... there's little left mechanically that can cause a problem.

Sorry to bang on - but you've not checked your isolator have you? You're certain that's ok then?

The isolator will deform over time and cause you problems. Replace it & I'd put money on that solving your problem. 50p bet? :smile: (I win either way)

 

About the 50p...................

I think that I have found the cause of the print failure. I have printed out the model completely (7 hours) but with "enable retraction" unchecked.

Due to the nature of the internal structure of bone the filament retraction was in overtime. Somehow, the retraction led to the filament not extruding and then the blockage. Yes there is some stringing, but I can live with this in order to get a complete print

MM

 

[tent 0]

hi. Ive been experiencing the same problem while printing head ct scans.. so you think the solution is to uncheck "enable retraction"? Is it possible to correct this by just adjusting retraction settings? Can any one comment on this?

 

[medicalmodeller 5]

The choice is yours. Either turn off retraction completely or leave it checked and change "minimal extrusion before retracting" to 0.4 or 0.5mm (in expert settings).

Post back to let us know if this does the trick

MM

 

[neotko 1,417]

I had similar problems with a totally different machine/setup (I'm using 1.75mm on UMO+). In the end the solution was to lower just a bit the speed of retraction. But ofc my solution probably isn't usefull. Btw, if you are using the stock feeder, go and print the IRobertI feeder, it's rock solid.