What's the Fan for? How to stop warping?

The fan by the extruder is not always going on. Right now I'm printing a long flat item and not sure if it's supposed to be on or there's a wrong setting or something. I can go into the Manual Control and turn it on.

Is the fan to cool the print or the extruder?

Also this piece is long and flat and starting to warp, will heating the bed help at all?

While I'm at it, why is the max temperature display in Repetier always 10* cooler than the extruder temp? i.e. the extruder temp is 180 and the range goes up to 170, or the extruder is 180 and it goes to 180.

Thanks.

 

That fan is the print cooling fan and is controlled by the gcode generated by the slicing software. One function is to quickly cool bridging extrusions which prevents bridges from drooping and allows pretty long bridge lengths.

The other function is to fully cool and solidify a layer before the next layer goes over it again. For large surface area layers this is not needed because there is plenty of time for each layer to cool. For small surface area layers the print time is small and cooling is needed to prevent printing over a still soft layer which can result in curling especially of thin edges.

If you use Slic3R check out the Filament Settings/Cooling tab. Auto cooling allows you to vary the cooling fan speed proportional to the layer time. You can be liberal with cooling for PLA but for ABS you need to be very careful and should avoid enabling it unless really necessary. Too much cooling will cause warping and can cause the print to pop off the bed.

I only control my printer with an XXL LCD so I can't answer the Repetier Host temperature questions. Sounds like it is just to make the graph pretty. The temperature will always overshoot before settling down to the target temp.

Your large flat print likely does not need any cooling.

 

Thanks, I had a very small part to print so hooked up an extra house fan, way too much cooling, it's a delicate balance.