MakerBot Industries

If you haven't already, I'd suggest carefully checking the thermocouple that is under a bolt on the extruder (I'm assuming you're using a stepstruder with a cartridge heater). Also check the wires connecting it to the extruder board, those screw fasteners sometimes appear to be tight but really are not making good connections. If either end is loose the thermocouple might not read accurately. Then the temp of the nozzle can get too high even thought the reading seems normal or low. That could flip the safety switch and shut off the cartridge heater as you describe happening. From my experience the thermocouple can easily come loose during operation.

Check this: http://wiki.makerbot.com/forum/t-432760/safety-cutoff-rev-c-problem happened the same to me few days ago.

Glad to hear it's working again, these things do sometimes seem to have a mind of their own:)

If you are using ABS and have to lift the temp to 235-240 I would suspect your thermocouple is reading higher than the actual temp. I have two ToM's to play with, one at home and one at the school where I work. On the one at home I usually leave the temp at the default of 225 and haven't had problems like you describe. On the one at school 225 is clearly too hot, we have been setting that to 195-200 to get the same results. So based on that small sample, and the fact that the thermocouple connection is a bit kludgy, I'd say you shouldn't put too much stock in the displayed temp, just use what works reliably. However, I don't think RepG likes it if you try to set a temp over 250, so if you continue to need to use higher and higher temps you might need to reseat the thermocouple or recalibrate the extruder head (something I haven't done but I believe you can change this in toolhead preferences).