To Fan the Nozzle or Not

I have printed mostly in PLA and a fan is pretty much mandatory.  I had thought that fans can be a problem with ABS but have been proven wrong by the results that I have seen both with and without a fan.  Below is a picture from the last post showing the difference between having a fan and not having a fan (left two Marvins).  These are prints in ABS.

The fan that I am used for these prints was downloaded from Thingiverse and is actually a duct that re-routes the extruder cooling fin fans to serve dual purposes.   It works pretty well as you can see.  Here is a picture of it mounted on my extruders. 

[UPDATE]----------------------------------------------

As much as I like this duct it seems to not like the fans on my printer!   Sucking hot air past the fans has killed them.  Other people report long use of this duct so I wonder if it is something about my printer or the fact that I ran a lot of ABS with these ducts in place?   I would recommend that you use carefully, and not for extended periods of time, if you are printing at ABS temperatures!

----------------------------------------------[UPDATE]

The fans have to be reversed for this duct to work.   There are comments on Thingiverse that expressed concerns that reversing the air flow could harm the extruders.  Counter comments explained that the airflow through the cooling fins is the same be it pushed or pulled.  That makes sense to me but I wanted to test it just to be sure.  I quickly adapted some hardware that I already had to wire up a temperature sensor that I inserted into the cooling fins of the left extruder.  I then did a print with the fan normally mounted with no duct and a print with the fan reversed and the duct mounted.  Here is a graph of the results.

Unfortunately the starting temperatures of my two test cases differed which is not what I had planned (though I obviously did not control for it either).  I don't, however, think that it matters given what happens in the tail end of the test case.  Namely that once the temperatures equalized they tracked each other.  Both fans having the same impact.  But I decided to run the test again.

And I still have not gotten two the two test cases to start at the same temperature though this time the differences are inverted.   Once again, however, the temperatures behind the heat sink stabilize.  The second test took a little longer as the starting point was a cooler printer than the first test.

Note that the print only ran for three or four minutes.  The other eight or nine minutes were warming up and cooling down.  The start of measurements was when the build platform reached 100c.  The end target was the extruder reaching 100c.  The print started at +4 minutes and +5 minutes, respectively, on the two tests.

Here are pictures of my data collection kit for the above tests.   The 3D printed case houses an Arduino Nano mounted with an LCD/TFT display, and an SD card reader, on a custom PCB that I designed as a experiments platform.

As you can see there is a header exposed that allows for different stuff to be attached to the platform, in this case a thermistor.   Inside the case are two headers that allow access to all Arduino Nano pins.  In this case there is also a little breadboard in there that has another resistor to create a voltage divider allowing me to measure the resistance of the thermistor.

BTW, the kit that I used will be on eBay in the coming weeks but if you are reading this and interested in an advance copy drop me a note.

The second picture shows the location of the thermistor.  Yes, I know, this is not exactly the top of the extruder but it is close enough as it is in the active cooling area of the fan.

The fan that I am working towards can also be downloaded from Thingiverse and is much more sophisticated.   The reason that it requires working towards is due to the challenge that it will be to print.   It requires a fan to print it.  Hence the above fan!

As I sat watching a print being made it occurred to me that I might have been worried about the wrong part of the extruder.  What if is the fan that is at risk?   In the reversed configuration it is getting hot air as input rather than cold air.  I wonder what it's temperature operating range is?  I guess I could measure this......or not!

[UPDATE]----------------------------------------------

All of the above is based on the flawed logic that inverting the fan might harm the extruder.  In practice it seems to have killed the fan!  I enjoyed the process so am leaving it in the blog...BUT...shortly after I finished this testing the fan on the ABS extruder started to make strange noises and now will not start.   The fan on the PLA side is also running loud now.  I have to conclude that heat being sucked into the fan is the culprit.   Since I know that I need a fan I am going to order one printed for me from a 3D Hub location and do this the right way.

----------------------------------------------[UPDATE]