Active cooling of J-Head insulator...

Construction of my self-build Mendel90 continues. Recently my new J-Head hot-end arrived, the final part of the jigsaw! Experience from my other printer has taught me that active cooling beneath the x-carriage has a number of positive benefits. Placement of a small fan that directs cooler air horizontally beneath the x-carriage causes a disruption to convected heat rising from the hot-end, preventing a temperature rise in the x-carriage that might cause deformation if overheated. It also cools the PEEK insulator on the J-Head which then maintains a short thermal transition zone, essential to prevent jamming. (There is a good illustration and explanation of thermal transition zone here on Nophead's blog.)

The current (at time of posting) Mendel90 x-carriage design didn't have a mounting point for such a fan. I had been designing a clip-on fan bracket when I saw Goopy's x-carriage modification to take a direct drive 1.75mm extruder, which included an under-carriage 40mm fan mount. Goopy's x-carriage wasn't suitable for me as he had also altered the carriage opening and extruder mounting-hole positions. So I imported the original x-carriage stl into Sketchup and modified it to meet my fan mounting needs. I also included M3 nut-traps into the design, which makes fitting the fan much easier, especially after the carriage is fitted to the printer. Goopy's lower shroud (half ducting) was of use as it directed the air flow above the stock cooling duct.

Illustrated above is the design change to the M90 x-carriage. 40mm fan mount. Design shared on Thingiverse.

Photo above/below shows first fit of 40mm fan and half-ducting.

Photo below shows new J-Head V in position. 

Below is a view from beneath the x-carriage, showing the new fan in position (right of pict) and the existing larger fan ducting for cooling the work. The half ducting on the new fan redirects air nicely up and over the larger ducting.

Finally below, a side view of the new fan mounted in position. It sits flush under the x-carriage resulting in no change in the length of the the carriage.

Controlling the fan:

The fan takes it's power via the ribbon cable to the x-carriage. The Mendel90 design has spare capacity on the 20 strands of ribbon cable that run to the x-carriage. I have the fan turning on/off automatically from the the Marlin firmware. A pin on the Azteeg X3 controller board becomes active when the temperature of the hot-end rises above 50deg C. This is all set is the ConfigurationAdv.h tab of Marlin (Section shown below.)

// Extruder cooling fans

// Configure fan pin outputs to automatically turn on/off when the associated

// extruder temperature is above/below EXTRUDER_AUTO_FAN_TEMPERATURE.

// Multiple extruders can be assigned to the same pin in which case 

// the fan will turn on when any selected extruder is above the threshold.

#define EXTRUDER_0_AUTO_FAN_PIN   5 //IOS 20130914 //-1

#define EXTRUDER_1_AUTO_FAN_PIN   -1

#define EXTRUDER_2_AUTO_FAN_PIN   -1

#define EXTRUDER_AUTO_FAN_TEMPERATURE 50

#define EXTRUDER_AUTO_FAN_SPEED   255  // == full speed 

The benefit of this is the fan operates automatically under firmware control, and I don't need to add any start/end g-code to drive it. It remains on after the job has finished, but automatically shuts off once the nozzle temperature has dropped below 50, or some other temperature specified in firmware section above.

Thanks for viewing!

Comments and questions welcome.

NumberSix

Cooling Fan speed control via Azteeg PWM Fan Pin Output

The Azteeg X3 Controller has four low powered outputs which can be used to drive fans or even LEDs. These outputs can be controlled by the host-software or called on when printing by gcode commands inserted by the slicing software. Marlin firmware is configured to call on the Azteeg pin D4 when the M106/M107 (Fan On/Off) gcode commands are used. (Azteeg full wiring diagram here.)

I'm currently experimenting with the Azteeg board controlled by Reperier-Host software and Marlin firmware onboard. That combination enabled immediate testing of the newly wired (two-wire) cooling fan on my 'scratch build' Mendel 90. But I soon found that despite the suggestion of possible speed control by Repetier-Host, with it's 0% - 100% Fan Output slider, the fan would only run when the slider control was near or at 100%. A little more research revealed that the simple two-wire fan could utilise the PWM (Pulse Width Modulation) Fan Pin Output of the Azteeg board if two simple common components, a capacitor and diode, were added to the fan circuit. I had to try it! (There was an article on the Bukobot site which gave full details on this hack: http://bukobot.com/pla-print-cooling-fan Credit and thanks!)

I first bread-boarded the two components to test that it would work... and it did! This basic set-up, the 10uF capacitor in parallel with the fan wires, and the common diode (1N4148 / 1N914 diode) in series on the negative wire provided the speed management of the fan.

I then placed the components on my stepper mounted connector board and wired them in. Pict below:

The following short video best shows fan speed control being tested.

The true benefit will come when I enable Auto Cooling within Slicer and the commands to switch on/off, and change cooling percentages are applied to the sliced gcode and called on during the print job. Slic3r now contains such settings... see screenshot below:

Other controller boards may also provide PWM Pin Output, and this simple two component addition to the  fan wiring gives great control of print cooling when combined with the Slic3r Auto-Cooling features.

Hope you found it of interest.

Thanks for viewing!
NumberSix