So this is what happens when spectra line breaks on my metric cerberus. First impressions are no serious damage done. I have excessive amounts of spectra to spare so getting it running again shouldn’t be too bad.
Is there any merit in attaching another line from the effector to a hook mounted on the ceiling? Just thinking out loud to avoid future occurrences. 
I love how you can see the line was stretching before it broke. Clearly on the section running from the top of the carriage, round the tensioner, to the spool.
@Neil_Darlow I don’t understand how that would help. I’m quite happy that the result was only 1) squirting plastic just off the bed, and 2) broken spectra that only took 1hour to re-string. I worry that doing anything to try to “help” might end up in something more expensive breaking.
@Bracken_Dawson I’m quite pleased about that too as it shows that I was actually working and paying no attention to the print that was running! 
It’s so hard not to stare at it while it’s running. That’s quite an accomplishment indeed! Was that 65# line? Do you think you had a seized tensioner pulley?
I thought spectra line was rated for over 100 pounds. How on earth did it break? How long was that strand in use before it broke?
The printer sure is pretty, even if broken.
Mine was 65lb but I have some 100lb on order now. Idler bearings and spools looked fine so I’ve put it back together. Test print had a few minor issues but no sign of serious problems.
Was it going REALLY fast?
Spectra is so tough. I tension mine by wrapping it around the threads of a carriage screw and tightening it down. The same 3 pieces survived this rough treatment and multiple dis/reassembles for more than a year! Even after it started fraying I let it go until it broke which happened on homing not printing.
I’ve had trouble with the line falling off the idler pulley and running on the axle when I’m first rigging it. But you would have noticed the slack when tensioning…
Spectra will definitely fail from abrasion. Hard to imagine you exceeded the breaking strength of 65 lb test, but hey, I suppose stranger things have happened.
How many total hours do you think you got out of it?
It’s been on the printer since Oct 2013 - less than 100hours printing time probably as it isn’t my only printer. The odd thing is that the wall of the print is clearly off distorting slowly throughout the duration of the print so it was obviously tightening over much of the duration of the print - which was less than one hour - until it finally gave out. It wasn’t printing fast just 50mm/s print speed and 150mm/s travel.
Hmm. Distorting toward or away from the failed tower?
Away. The failed tower is the front left in most of the pictures.
what do you think caused the line to break?
It looks to me like the break happened up by the idler pulley?
Abrasion is my guess. I often find my pulleys will collect stuff and sometimes stop turning.
@Robert_Swarner Great insight. That would seem to be the most plausible explanation.