defcon3d - Hey Vinnie,
Check this post out.
https://groups.google.com/forum/#!searchin/makerbot/abs$20prints$20cracking/makerbot/vRcDQv7G0EE/f2yLlilAWC0J

Have you enclosed the build chamber to get uniform heat across the print? That will also give you uniform cooling...
On big parts ABS is much finicky to work with then PLA..

vinnie90 - I normally just do all around. When I put the lid on top it gets extremely hot. Hot enough that the frame is really hot and it even starts to melt the filament before it gets to the extruder gear.

vinnie90 - I normally just do all around. When I put the lid on top it gets extremely hot. Hot enough that the frame is really hot and it even starts to melt the filament before it gets to the extruder gear.

n23d - One thing I found that helps is to set your nozzle diameter larger than the physical nozzle diameter and your layer thickness less than the physical nozzle diameter. This forces the plastic to make good physical contact with the previous layer. The combination of increasing the flow of hot plastic into the weld zone and good physical contact improves the bond. I believe there are some advanced settings in slic3r that can do the same thing however I have not played with them much.

vinnie90 - nice concept I might have to try that one

shortrun3d.com - Your cracking is the result of the ABS contracting as it cools down. The concept behind enclosed printers is that the heated build plate and the extruders create enough heat to maintain a higher ambient temperature in the printer which prevents the printed ABS part from cooling and contracting and thus cracking the part. I would suggest closing up your machine like you did but keep an eye on the ambient temp, you should be able to toy with having the enclosure opened just enough that the temp doesn't get to hot, there will be a sweet spot with no cracks and no over heating of your machine. Also you might have your build plate to hot if you are getting getting the inside of the machine as toasty as you claim. Try brining it down to 90c on either kapton or hairsprayed glass.

vinnie90 - Ok trying it out today Shortrun3d.com

sd3dprinting - All of these suggestions definitely help and are common practices when printing with ABS or nylon, but it will not solve the problem completely. We got fed up with dealing with cracking and warping years ago and needed a better solution for production printing. This was one of the main justifications for bringing our Adaptive Build Environment to market. ABE provides active temperature gradient neutralization to completely solve the problem of warping and cracking: http://sd3dprinting.com/abe-adaptive-build-environment/

vinnie90 - It was working.....But started to crack the same amount as before.got about 6 line cracks in it

Bed at 90 and completely enclosed

sd3dprinting - As shortrun3d pointed out, the elevated temperatures of the build environment will slow down the cooling of the part, but interlayer stresses are not caused by part cooling in itself, they are caused by temperature gradients which lead to UNEVEN part cooling.That is why you will still get some warping and cracking within non-controlled enclosures. The heat generating components on the printer itself can cause enough of a temperature gradient inside the enclosed environment to produce warping/cracking. Your heated bed likely also has it's own surface temperature gradients in excess of 8 degrees C at steady state and likely much more than that during the heat-up and cool-down phase which causes severe stresses on the printed part, leading to additional delamination. Both the bed and environmental temperature gradients need to be actively controlled if you are going to completely cure cracking on tall ABS prints. Messing around with the slicing settings as has been suggested may give you better interlayer adhesion adhesion but there will be some tradeoffs in dimensional accuracy and strength, as those stresses will still be built into the part, even if you manage to pull it off the bed without any visible cracks.

j1ceasar@yahoo.com - try a small fan across the project to even out temps