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extruder hits print after some time printing  

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janos.s
(@janos-s)
Active Member
extruder hits print after some time printing

I have a problem that the extruder often crashes into the print after some time and ultimately knocks the print of the heat bed.
It is really hard to figure out what causes this. After printing a few cm height I can hear the extruder knocking against the print each layer at the same position. After a few knocks the print detaches and the print fails.

Printing the V2 calibration code works just fine and the problem does not appear at the first layers.

I think it might be that the z axis is a little bit loose on one side. I am thinking about replacing the nuts on the threaded rod of the z axis by brass nuts found on eBay
http://www.ebay.de/itm/331960886071?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
However I am not sure if this is really the problem.

It might also be caused by warping of the print which causes some pieces to curl upwards. I have not really seen warping but maybe I missed it because it was lifting only a fraction of a Millimeter.

Does someone have experience with this kind of problem?

Posted : 18/11/2016 9:47 pm
JohnnyricoMC
(@johnnyricomc)
Estimable Member
Re: extruder hits print after some time printing

What material are you printing with? Are the edges of your print lifting off the bed by any chance?

Posted : 18/11/2016 10:39 pm
MrMik
(@mrmik)
Honorable Member
Re: extruder hits print after some time printing

At which z-height does it occur?

You could just print something that will not warp, to determine definitively if there is something wrong with your z-axis.

In OpenScad you can create a cylinder, then export as .stl file, then use Slic3r to make a .gcode file and then print it.

OpenScad text:
$fn=70;
cylinder(h=50,r1=15,r2=3);

I find it most useful to watch live and close up what happens, it really helps to figure out what goes wrong, but uses much time.

Posted : 18/11/2016 10:53 pm
PJR
 PJR
(@pjr)
Antient Member Moderator
Re: extruder hits print after some time printing

Three possible solutions:

1. Slow down the print - this will allow more cooling time and prevent warping.
2. Slice with Z-Lift - the nozzle will be lifted on all non-printing moves
3. Print with a brim - this will help to prevent the part lifting.

But all this depends on your model and slicer settings.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…

Posted : 18/11/2016 11:31 pm
janos.s
(@janos-s)
Active Member
Topic starter answered:
Re: extruder hits print after some time printing

I noticed this problem with the Plattform Jack four times in a row always around the same height.
It is likely that some parts are detaching for this model but once i heard the knocking, stopped the print and was not able to see any part being tilted, detached or higher than the others.

Adding a rim did not help but I tried the same print with two solid layers raft beneath it and it finally worked.

Maybe it is really just warping and I need to be extra careful about it. The big dragon that is always depicted on the prusa mk2 printed without any problems. I will print more things and watch closely before I start modifying the z axis of the printer.

I am printing PLA with 210°C extruder and 55-60°C heatbed temp.

Posted : 19/11/2016 12:34 am
janos.s
(@janos-s)
Active Member
Topic starter answered:
Re: extruder hits print after some time printing

Several tests later i am convinced that all my problems are related to warping. If one of the edges lifts a millimeter the consequences can be severe!
A little bit of play on the Z axis is not a real problem.

Thanks for the help!

I am still not sure which kind of prints are most likely to warp but there should be a lot on the internet about this topic.

Posted : 26/11/2016 5:06 pm
MrMik
(@mrmik)
Honorable Member
Re: extruder hits print after some time printing

Three possible solutions:

1. Slow down the print - this will allow more cooling time and prevent warping.
...
...

Why does it reduce warping when you print more slowly?

And how does that relate to bed and air temperature?

Posted : 27/11/2016 12:02 pm
PJR
 PJR
(@pjr)
Antient Member Moderator
Re: extruder hits print after some time printing

All these things depend on the model.

Printing slower, allows more cool-down time for each layer. It is hot-on-hot which can generate warping of prints with PLA and some models.

Just one more thing to try...

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…

Posted : 27/11/2016 9:51 pm
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