<p>I'm trying to print large objects (around 1 meter squared) with polycarbonate pellets. The problem is sometimes the print cracks. It is not due to delamination as it is a shear crack across multiple layers. I know the ideal scenario is to have a heated enclosure but I cannot do that due to the size. Any suggestions?</p>
<p>I am using a robotic arm (KUKA KR360) with a custom extruder. That is why I can't build the enclosure. As for the temperature, they are 230 to 260 °C. Nozzle is 10 mm.</p>
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<p><em>I like the idea of directed heat. I might try that.</em></p>

Printing polycarbonate requires a high end 3D printer that is suitable for the task.
From
Simplify3d support
we learn that:
... requires very high temperatures for printing and will
exhibit layer separation if printed at too low of a temperature or with excessive cooling enabled
. Polycarbonate is frequently
best printed on a machine that has an enclosed build volume
and is capable of handling high bed and extruder temperatures.
High temperatures and enclosed build volume are key to print polycarbonate without cracking or delamination.
Any suggestions?
Note that NASA has successfully printed ULTEM (even higher temperatures needed)
using open source hardware
. They have used infrared lamps directed at the build plate, this may be an option if a full enclosure is not possible. Also people seem to get good results with draft shields for printing ABS on non enclosed printers. Key is that a constant elevated temperature is created near the print, whether that works for such a large size remains to be seen. Best solution would be enclosing the printer.