Note : this article relates to ABS printing only. REferences and solutions in some cases refer to the Makerbot Replactor 1 (ply wood model)
This page is dedicated to the failed print! Why did it fail? What is causing your problems? How do you fix it!
The most common tech support question we get is “why did my print fail?”. Nine times out of ten times the answer is environmental issues. The good news is they are easy to diagnose and easy to fix; but first lets talk about some of the basics.
What are Environmental Issues?
Put simply these are issues that relate to the environment around your print that influence the success of the print, but that are not related to the machine, filament or the heater bed (or the surface of the bed). They fall under 3 categories : Convection Current, Drafts and Ambient Air Temperature. 
a) Convection Current :What you need to understand is the influence environment has on the print and the printer bed has on the environment. You see, as your heater bed warms up the air above the bed warms up. Warm air rises drawing in cool air from the sides (or front) of the bed in towards the middle of the bed and effectively into you print. This convection current is an unavoidable side affect of the technology, and can result in print fails (detailed below).
b) Drafts : Then there are drafts! You may not think there is a draft coming across your print bed, however if there are you will find all sorts of print fails result. These can come from an open window or an air-condition system, for example, and do not have to be very strong to have a dramatic effect on your print success rate.
c) Ambient Air Temperature : This is the temperature of the air that surrounds your machine and printer bed. The warmer this is the less convection current and slower and more evenly your print will cool! 
Is your print cooling more on one side verses another or at the edges significantly faster than the middle causing curling and lifting off the bed? These are examples of an Environment Issue Fail.
Most Environmental fails can be fixed by:
a) Pop your printer in a box (or adding windows and a hood to the Replicator).
Why it works : Keeping a stable temperature around your build means your print will cool evenly.
b) Running Preheat longer – to increase ambient air temperature pre printing
Why it works : Increasing the preheat time increases the temperature of the air around your bed. Heating up the bed during the print slows down cooling and thus “setting” of your printed model. One of the key reasons the build slips off the bed a few layers up is because the base layers have cooled and contacted. ABS needs a temperature of around 200 degrees to liquefy for printing. If your bed is not warm enough, or the air around your print out is too cool, your print out will cool, contact and pop off your bed. Common Problems you might see when environmental factors are at play
Non-Environmental Fails
Non environmental factors causing print fails include :
a) Heater bed surface : If you are using Kapton tape do not rule out just replacing it. On average you should get 10 or more prints from your tape, but it can easily wear, especially in frequently used areas and in the corner of prints, where you start lifting your print off the bed. You can also scratch the surface when removing prints; and your fingers have oil residue that you can transfer onto the bed when laying the tape and removing prints.
Other alternatives to Kapton: You can also use Blue Painters Tape, which provides better grip, especially with oilier filaments. Some people print on glass, perforated fiberglass boards and other surfaces. I can not comment on these personally, although I am interested in 5mm+ glass.
b) Filament fail : Sometimes, even in the most expensive filament, you get bad filament. This can include thinning (where the diameter is smaller than it should be), bulges (swollen areas that block nozzles); grit in the filament (foreign particles that should not be there and can block the nozzle), too high an oil content; dust (statically collects on the outside of filament and can cause nozzle blockages, although not very common). These can all cause a print to fail.
c) Nozzle height : This is one you will get a feel for over time. In general, if the nozzle is too high, you may get holes in the print, poor adhesion to the bed, 1st or 2nd layers look ok but then the print slides right off the bed. In the picture right (going left to right) each print has a nozzle height .1mm closer to the bed, so you can see the effect nozzle height can have.
d) Code error : Sometimes it is the STL or GCODE that is at fault. How do you know if this is the cause? You will get exactly the same error in exactly the same location every time. For example, in the Maoi pictured here there is a Gcode error rendered through Replicator G and printed on the Replicator. The pimple like surface may appear random, but ever time you print this set of gcode the pimples would be in exactly the same place. To confirm this we took the same STL onto an UP and rendered the GCODE in its software and the pimples were gone. We then went back to the Replicator G software, reloaded the STL and generated the Gcode again, pimples gone – sometimes things just go wrong in the rendering/conversion process.
On the otherhand, sometimes it is the source code (the STL model) that is at fault and not the printer or software at all. Zoom in on the model at the error point and have a good look at the file – is the error in the file?
e) Just one of those things : Sometimes stuff just happens. Computers lock up, power fluctuates, the moon turns blue…it just doesn’t work. The trick is to notice trends/patterns. “Insanity is doing the same thing over and over again and expecting a different results" Albert Einstein.
Lee Bilby
4 Sep 2012