One of My Two Fans is Whirling Back and Forth

[w22]

Never heard this before, while my print prints, everything seems fine but I can hear one of the fans sound like they are attempting to start up, I hear it whirl, and then I hear it go back down to a different speed all within two seconds, every two seconds.

What's really odd is the Fan #2 (the bigger one, correct me if that is Fan #1), never spins at all which I know is sometimes normal, so it must be the extruder fan but I never see it actually stop spinning the entire time.

[Jules]

The fans are controlled by various bits of G-code that get implemented during the printing process.

For the Rev E machines, when you turn that printer on, there is a bit of code in the firmware that turns the fans on for a second and then turns it off as the unit powers up. That firmware also turns on the extruder fan as the hotend heats up, and keeps it running after the print ends until the extruder temperature cools down.

While the extruder is hot, that fan is going to stay on depending on the temperature that gets sent back to the controller - you can't control that one except through the firmware. The fluctuations might be a sign of something going on with the temperature, or you might be hearing something else.

You are responsible for turning on the Bed Fan if you want to use it, on the Cooling Tab in S3D. It has two speeds, off and 100%. You set the speed based on the layer - most people use zero fan for layer 1 and maybe 2 to help PLA stick, then 100% for all other layers. Different filaments have different cooling requirements. Usually you will see the bed fan kick on after layer 1 for PLA, and it is not turned on at all for ABS.

So watch closely when you run a print and check the instructions in the Cooling Tab to see if it's doing what you told it to.

[w22]

All temps are normal but I still do hear the shutdown of the fan and then it initiating again. It is most definitley the extruder fan and it's happening all throughout every print, no matter what print it is, nor where the print is coming from.

[ednisley]

it's happening all throughout every print

The models you show here tend to have ... unusual ... geometry. If the slicing parameters call for cooling on bridges, you'll see little bursts of fan motion whenever the slicer detects anything that it thinks is a bridge, even if it's a millimeter wide. For very short bridges, the fan will just barely twitch before the nozzle is off the far side of the bridge.

If you know a specific model doesn't have any significant bridges, then you can turn off bridge cooling when you slice it and see if that changes anything.

[w22]

Wonderful! Thank you for your input as always and just for kicks, I've attached the current print that is whirling every ten seconds or so.

[ednisley]

attached the current print

Meshlab shows a gazillion self-intersecting faces, so that model isn't ready for slicing.

Fluted vase - self-intersecting faces

That also explains why it blows up when you (try to) cut it across the middle: the geometry remaining after shearing those broken faces isn't valid.