Why add a Fan at Extruder-nozzles ? (Page 1 of 3)

You're not trying to cool the nozzle, but the filament as it exits the nozzle.  This makes a big difference with bridges and overhangs.  The fan speed can be controlled manually, or through g-code.

You are correct though, you don't want to direct the air onto the nozzle itself, just at the filament.

Honestly, this is probably the most impactful mod you can do.  Here is the results of an experiment where I ran the same gcode with and without fan.  It will give you much beter quality on overhangs.  I almost never turn on support material anymore.

Yes our printers have full nozzle temp control.  The fan has nothing to do with the nozzle temp.  Accurate PID tuning of the nozzle temp will yield a perfect flat line temp.  The nozzle fan is used to do many things.

On very small prints it is used to cool the layers just enough that the print doesn't deform before the next layer goes down.

It is used with great results for bridging as it will cool the filament just enough to allow it to stretch tight.

It also helps greatly with steep overhangs that would normally require support.

Your theory of a nozzle fan messing up layer adhesion is not true.  Think about a large print, by the time the nozzle gets back to a particular location for the next layer,  the previous layer most certainly isn't still at or beyond the transition point.
You always are printing on a layer of cooler plastic so no worries about that.

My advice is, if you've never experienced a good G-code controlled nozzle fan, try it!

Do you happen to know of a good place to get more Info about "PID tuning" ?

I think I understand what it IS, (feedback loop controller)
but Not how to accurately Tune it ??

I previously encountered PID in a Ships-Helm control but I guess that is a Little Different ? LOL

Yes, I have noticed that, Thanks for Info !
Now I need to print a Fan Funnel ! LOL

But what if you are using software, like Makerbot, that the G-code can Not be edited ?
Is there a way to software control that added fan on those printers ?
Or is Manual speed control the only option ?

There are several on thingiverse that are made to use the existing clip points on the CTC printers. I made one for mine... Just look for Flashforge Creator cooling fan. It is the same as the CTC..

http://www.thingiverse.com/thing:537918

Thanks for Info !
but that refers to Software and programming that is Very Different from any we are using.

Hopefully someone will  develop GUI software soon that will allow us to just put in temp numbers,
and Not have edit the programming code (gcode)

Until then we will probably just try a fan connected to a small adjustable external power-supply,
so it won't be drawing power from printer's power-supply.

You maybe don't have EEPROM interface but it is certainly in the firmware.  Of course that doesn't help either if you don't have access to a copy of that.

What are they using for a board on that thing?  Is it running a proprietary firmware?

I thought the CTC was a makerbot clone.  How can they use Makerbots proprietary firmware?

So why couldn't just be re flashed with Marlin?  Just trying to learn more.