It has been at least two months since I last played around with using a cooling fan while 3D printing. My first attempts were an old pedestal fan awkwardly tilted to cool the build platform. But I largely abandoned using a cooling fan while I was mucking around with other printing parameters.
However, now that I am happier with many other aspects of 3D printing I was running into problems with printing bridges and overhangs cleanly. Anytime I tried to print in mid air, the plastic bridge would come out all saggy and would require a fair amount of cleaning up with a Dremel after the print had finished.
So I added a 80mm cooling fan to my setup. I wired it straight into the spare D9 port on my RAMPS 1.4 controller and updated my Marlin firmware motherboard configuration to use the following motherboard type:
// RAMPS 1.3 = 33 (Power outputs: Extruder, Bed, Fan)
To mount the fan, I grabbed this excellent fan mount design from thingiverse. The instructions recommended bolts, however I snapped the little attachment tabs when I was pushing the mount onto the 8mm threaded rod. So used a couple of cable ties, that attached it snugly, this also works nicely as a hinge so that I can swing it the fan of the way to get access to the build platform.
Initial results are awesome, I can now print 25mm bridges without any appreciable sagging (see below). As an added bonus improvement, the layer height also appears to be considerably more consistent. The Marlin firmware intelligently controls the fan, so that it will be switched on for layers that have a small area. No more sagging and collapsing of solid layers when you try printing on top of them before they have had the chance to cool and harden. In my opinion, I don’t think a cooling fan is an optional extra, and should come standard with 3D printers.
Running the fan at maximum speed actually cools my buddaschnozzle hotend down enough to trigger the Marlin cold extrusion safety switch. It can drop my hotend temperatures from 185°c to 177°c in about two seconds. I will need to tweak slic3r settings to work out the ideal fan speed.
I also might add a second fan on the opposite side of the printer. Sometimes the print head obstructs the part of the print that needs cooling from the airflow, or perhaps get a smaller fan that I can mount directly on the X-carriage. That way I should also avoid the above problem as well.
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