Thermal Runaway -- any way to modify this?  

Active Member

Hi Again,

While I do have troubles printing PLA on the prusa, PETG seems to work just fine, so I'm focusing on that for now.

One of the issues I've noticed with PETG is that it doesn't bridge as well as PLA.  In an effort to address this, Simplify3D has some pretty nifty options. One of them is the Bridging Fan Speed Override. For one layer, if a bridge is detected, you can increase the fan speed (or decrease it, though I straing to find an instance where you would want to do that!) causing the melted filament to solidify faster, and not droop as much.

So, on my print in question, I'm printing with 15% on the part cooling fan.  When it detects the first layer of a bridge, it shoots up to 100%. I happened to be present to watch it print, and as soon as it hit the first bridge, I heard the fan kick in. It started printing the overhang, and everything was looking really good.  It got about 1/4 of the way through, and I got the "Thermal Runaway" error (not a "Bed thermal runaway").  I'm 90% sure that this occurred because the fan suddenly kicking up to 100% dropped the nozzle temperature beyond the 15 degree threshold for a moment there.  The terrible thing was, there was no way to recover, and I lost the print.

Is there any way to temporarily change this threshold?  Or even tell it to turn off thermal runaway for a single layer?  I understand that it would be foolish to do away with this important safety feature completely, but a single layer should be pretty safe.

I know I could create multiple processes to address this... but then that pretty much annihilates the purpose of the bridge-tweaking features of S3D, and of course, adds more set up time.

Any ideas on how this could be deftly addressed?



This topic was modified 2 months ago by chris.d39
Posted : 08/04/2020 8:01 pm
Noble Member

Best way to ‘fix’ this is to fit a sock, they are relatively cheap silicone covers that fit over the heat block. They wear out over time so buy a few at the same time. As well as insulating the extruded they have the side benefit of protecting it should your print break loose and cause a ‘blob of doom”. Do a PID run once fitted so the firmware can learn the new thermal curve.

Btw fan speed for bridging is also part of Slicer too so it’s not unique to s3d. 

Posted : 08/04/2020 8:11 pm
Active Member


Cool.  Thanks.  I will get a sock for it then, and re-do the PID. Thank you.




Posted : 08/04/2020 8:32 pm

Please Login or Register