Print w/ ABS cracked using heated bed

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Got my heated bed all hooked up this weekend along with my new abs. Was doing some test prints and came along this problem:

 

I linked above to the 39 second point where you'll see a crack develop and start to open up. Any clues as to why this might be happening or how to prevent it?

[Daid 306]

My guess it's the same forces that cause warping. You could reduce the cooling, and increase the temperature a bit so the layers stick better. Or create a heated chamber.

[joergen 2]

Daid is right, your printing temperature is probably a couple of degrees too low, causing bad layer adhesion. but the same force will also rip your print off the platform if you don't decrease the cooling. try a M106 S64 and see if that helps.

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I've been running it without the fan on at all. Could this also be a source of the problem?

Also, i just ran another test and stopped it due to warping and some abs 'booger' buildup in one spot. See the below photo:

This is on a heated bed, no fan running, running Cura 12.07. Packing density set to .85 and pretty much everything else is default

[joergen 2]

This is on a heated bed, no fan running, running Cura 12.07. Packing density set to .85 and pretty much everything else is default

yes, you need some cooling. some light 25% fan should help with the goo, and also lowering the speed might help, to give the ABS a chance to solidify.

In addition, the packing density of 0.85 in Cura is (very) wrong: this leads to severe over-extrusion, and no amount of cooling will help you making a nice print. I would suggest to dial it back to something like 0.96, and then adjust the flow if you think you are still over/under extruding.

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Joergen,

That was a huge help! Changing the packing density to .96 and setting the fan to run at 25% made a big improvement. Still have a little way to go but those 2 tips were a huge step forward. Thanks