Cracks in models? What causes this?

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lachie_h
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Joined: Thu Aug 15, 2013 12:18 am

Cracks in models? What causes this?

Post by lachie_h »

I've been having a bit of drama trying to get print settings right and having not much luck.

I originally had problems with the ABS filament not sticking to the base properly due to curling and thought I'd try all of the recommendations to solve it. It's still happening, but much less and I think the cause of the curling is being cause by a different problem.

The problem I seem to be having is that I'm getting cracks between layers for most of my prints. I looked into it and found that most people reported it to be a cooling/heat issue.

I'm using Repetier Host and Skeinforge/SFACT to do the slicing. I haven't changed many of the settings from default apart from the minimum angle to need support material and the size of the raft.

Have a look at these two pics:

Print 1: 190ºC print head and 75ºC base at 100% speed.
Look at all those cracks. The model actually broke coming out of the support material because of how many cracks it has.
Image

Print 2: 205ºC print head and 85ºC base at 50% speed.
Thought it best to print slower, giving the layers more time to cool after being extruded at a higher temp. Notice there is less cracks, but still enough to warp the model causing the extruder to catch and make a giant turd on top after pulling the model off the base.
Image

I've gone through the Common Tips and Tricks, trawled through most of the threads and still no luck.

TL;DR: Models are showing cracks and I don't know how to fix.

What am I doing wrong?

seaton
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Post by seaton »

is it ABS that the problem is happening with? If so then I think its a fairly common problem and Ive yet to play around with ABS myself, at the moment I've kept away from it.

What do you have the fill set to? maybe you could try a different fill setting, maybe less than what you're currently using?

Is the fan on when printing, maybe you could try with it off?
Stephen...

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satoer
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Post by satoer »

ABS needs a way higher temperature then 205 degrees. Try 230 degrees.
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Saamec
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Post by Saamec »

Speed for ABS plastic should be equal to 30-60, the less the better. He's worse than melts, and he had a large viscosity. In addition not all plastics are the same. I advise you to stay on the plastics of the USA. Temperature extruder should be not less than 230 degrees. Well, bursts model because of tensions inside the plastic. It means you are uneven cooling. The reason - fan, because it blows only there where extruder, and blows from ONE side!!! The second party does not receive such cooling. The difference in temperatures and leads to cracks.

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superhornet59
Posts: 60
Joined: Wed Apr 03, 2013 1:58 am

Post by superhornet59 »

+1 for increasing extruder temp. By exruding too cold, the layers won't stick very well.Combine this with ABS's high coefficient of thermal expansion, it warps as it cools and literally tears itself apart at the weakest-bonded layers.

You should print slower, and disable the fan whenever possible (if you need to things like shallow overhangs/brides then that's a different story). Also crank that heated bed up. It's unfortunate because most people agree that your heated bed should be at something like 100+ degrees, but the Felix carriage/extruder will begin to deform once subjected to that kind of temperate (and the bed only goes to like 85-90 degrees anyway), so you have to keep it at around 60. If you can re-print the whole extruder out of ABS, then you could crank up the temps and really see some results.

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