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curieux

Cracks on ABS

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[edit by gr - note that:

original post said PLA but it's actually ABS

]

 

Can anybody explain where this cracks coming from ?

( no cover , air draft )

 

 

thx in advance

 

cracks-madam.png

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If the cracks go all the way around then it's most likely Z axis errors.  The Z axis probably sometimes moves not far enough - and then other times it moves too far.  When it moves not far enough you get over extrusion and the layer sticks out a bit.  When it moves too far you get underextrusion exactly like these cracks.  

 

Usually cleaning the screw very well will fix this issue.  Note that most Z screws are double, triple or even quad helixes so make sure you clean out them all very well.

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14 hours ago, gr5 said:

If the cracks go all the way around then it's most likely Z axis errors.  The Z axis probably sometimes moves not far enough - and then other times it moves too far.  When it moves not far enough you get over extrusion and the layer sticks out a bit.  When it moves too far you get underextrusion exactly like these cracks.  

 

Usually cleaning the screw very well will fix this issue.  Note that most Z screws are double, triple or even quad helixes so make sure you clean out them all very well.

For my own edification, What could it be if it just in odd areas and not all the way around?

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I forgot to say :

I had the issue with UM2+ and ABS  . S3D was used as slicer program.

Also support material was used

 

The Cracks does not go around  see attach

 

 

 

cracks1.jpg

Edited by curieux

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Maybe try pulling it apart? If it is caused by poor layer adhesion combined with warping (which I guess it is indeed), then bonding should be so weak that the model can easily be pulled apart. Not only on the visible splits, but also on other parts without visible defects. It should sort of delaminate.

 

If it is a Z-axis problem but good layer adhesion, pulling it apart should be much harder. At least, I think so...

 

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I've seen these cracks on ABS but NEVER on PLA.  Are you sure this is PLA?  Is it some "high temp" PLA?  Try this experiment:

 

boil some water in a tea cup.  put some filament in and a thermometer.  Find out what temperature the PLA goes soft and what temperature it goes hard.  It should be around 52C for PLA.  Around 99C for ABS.  You may have some new formulation of PLA that goes soft at 80C or maybe it's mislabelled.

 

The reason ABS cracks:

Two reasons - one is bad layer bonding but this is in combination with much more shrinkage from the softening temp down to air temp.  Basically both reasons that ABS cracks easily while you are still printing are the same reason - high softening temp and high melt temp.

 

It's possible you have too powerful a fan and the air temp is too cold (20C) such that the layers are cooling too much (seems impossible with PLA but maybe it's possible with a really powerful fan) such that your layer bonding is bad combined with shrinkage causes it to crack.  This seems so unlikely with PLA.

 

I suppose if you printed with very strong fan *and* air temp was at 0C (freezing temp) you might be able to get PLA to crack like that.

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30 minutes ago, gr5 said:

...  Are you sure this is PLA? ...

Yes, this is the right question. Upon seeing that photo, I simply assumed it was ABS; I hadn't even noticed the word "PLA" in the title.  :)

 

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4 hours ago, curieux said:

Its ABS

OH SNAP!!!!!!!!!!!1

Okay.  Well that changes everything of course.  It really looked like ABS.  I changed the title of this topic.

 

Well you have bad layer adhesion.  You should enclose the machine and heat the air to 35C.  Or raise the nozzle temp.  

 

ABS has a *very* narrow range of printing temps because if you are too cold you don't get good layer adhesion and if you go to hot the ABS cooks into a kind of gummy gunk that causes a semi-permanent clog in the nozzle.  You can remove it by heating the nozzle over fire and removing with a toothpick.  Particularly this will happen if you leave the nozzle hot for a few minutes but don't print.  Increaseing by 5C can cause the problem.  The last time I got an ABS nozzle clog I was printing at 255C.  I usually print at 254C now, lol.  But if I stop printing and keep the nozzle hot for a few minutes I'm sure even at 254C I'll get a clog.  Your mileage may vary.  Different printers are a few C different.

 

Another solution is to print thicker layers.  If you print 0.2mm layers versus what looks like 0.06mm layers the added mass of plastic pressing against the lower layer is more successful at heating the lower layer up.

 

Really the best solution is to use ANYTHING but ABS.  PLA prints the most beautiful.  For things that need higher temps you could try nGen or PET.  Those are in-between in difficulty.  Here is a chart of suggestions - scroll to the second chart - the ones in green can't handle high temps as much.  Yellow filaments are a good compromise - higher temp - but still easy to print.

 

http://gr5.org/mat/

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