I've been designing and printing all kinds of cooling ducts for the last 2 months as I just wasn't happy with what I had. Even the popular round ducted coolers just don't do a good job in directly cooling the filament whilst keeping the heat block hot. Also many found on the net are too clunky, too heavy or are IMHO just terribly designed.
With the new Marlin and other 3D printer firmware's incorporating thermal protection mechanism it now becomes even more important to have a design that will not cause false alarms. This is particularly the case when the cooling ducts blow air on the heat block and not on the filament.

Design objectives:

• Blow high volume air on the filament just beyond the nozzle.
• Avoid as much as possible in getting cooling air on the nozzle/heat block.
• Create a design that will not disrupt the view surrounding the nozzle.
• Make it easy to get to the nozzle with tweezers to remove filament.
• Create a version that can easily be printed.
• Make it as light as possible to avoid high mass on the extruder. It weighs 2.8 grams.

At the end of the day I have found that this design outperforms anything I had been testing so far.

Attention:

• This cooling duct is intended for use with the standard unmodified A8 printer.
• It is recommended that the cooler be printed in ABS or PETG as these filaments are more heat resistant. However I have mine printed in PLA without any issues. When printing ABS or high temp filaments I just remove the cooler. You normally don't print with the fan on for high temp filaments.
• With this cooler you might need to reduce airflow with some prints! Sometimes I have to print with 75% or less where in the past air flow was set to 100%.

I want to thank Jan Hedström for testing this cooling duct and confirming the effectiveness.
Also thanks for the idea of giving it a cool name "Mistral"!

Please let me know if you have a problem with the design so I can improve it if necessary.

Also please post a picture with comments if you have made one.

Thanks.

Leo

If you are using SkyNet3D then you can use a function to calibrate your extruder nozzle via „PID Autotuning“.
You will already find PID values in the firmware however it is a good idea to set them according to your surroundings.

This is how to calibrate the hotend:

First we need to get the PID values from the hotend. The values are read in 8 cycles using the following code:

M106
M303 E-0 S210 C8

Code description:

• M106 run nozzle at 100%
• M303 start PID autotuning
• E-0 select the first hotend
• S210 set extruder temperature. Here we chose 210°C
• C8 denotes the number of cycles. In this example 8

After the 8 cycles have completed you will see something like this:

Kp 14.68
Ki 0.70
Kd 76.59

Now you will need to save the values to the printers eeprom:

M301 P14.68 I0.70 D76.59
M500

Code description:

• M301 temporary sets the PID values
• P = Kp
• I = Ki
• D = Kd
• M500 will save the temporary PID values to eeprom.

More information can be found here: http://reprap.org/wiki/PID_Tuning

I've added a thicker walled (1.2mm) version 1.0a to the files section. In my opinion the standard (0.8mm) thick version 1.0 is best used, however some users have asked for a "beefier" cooling duct.

I've uploaded a new version "Mistral 2" as an alternative depending on your needs: http://www.thingiverse.com/thing:2121279