Case Fans/ positive/negative pressure/best practices
Hey guys,
I do not own a prusa (but I'd like to one day....) I have been playing with various slicers and I like prusaslicer so much I decided to join this community. I see a lot of you have built enclosures for your printers so I though maybe someone could give advice on case fans. Some background on my printer:
It's a Davinci 1.0. This thing comes fully enclosed from the factory and no cooling whatsoever (not even a layer fan) as it was originally intended for ABS. I ditched the horrendous hotend and built a custom X-carraige that uses drylin bearings and converted the proprietary direct drive hotend to a bowden E3D v6. I incorporated a 40mm centrifugal fan on the carraige that blows directly on the nozzle for layer cooling. I am able to print PLA fairly well, but I do have to slow my print speed down on very short layers. I have gone down the road of various ducts, two fans, blowers, axials, you name it. I've gotten the best results with one of these:
mounted on the side of the carraige with the short (and somewhat broad) duct about 20mm away from the nozzle. I like this fan because it's a very low profile, and the duct is securely mounted and adds very little mass to the assembly. Initially i wanted to add another one on the opposite side, but that was complicated by the wires for the thermistor and heater cartridge being run on that side so I have resigned myself to just one fan on the printhead. I have approximately 500ma (.5amps) of headroom on the transistor that drives the cooling circuit. Which is enough to add at least two 60mm axial fans on the windows of the enclosure.
I did some testing with this:
mounted in the left side cutout of the enclosure:
I had the fans blowing out of the case (exhaust) opposite side of the layer cooling fan (flowing same direction) my line of thinking was that the position of the layer fan is well-controlled (attached to carraige) blowing cool air on the layer, so adding exhaust fans on the opposite side of the case would pick up the hot air and carry it away from the layer. I did a simple bridge length test to evaluate this setup and my results were actually worse with the case fans in an exhaust configuration. My hypothesis is that this created too much negative pressure in the case and the layer fan was starved of air? I was concerned that arranging these fans as intake would create turbulence and the layer fan would not be able to straighten it out and direct it as efficiently. There are two more configurations untested, both fans as intake, or one for intake, one for exhaust. there is also a fourth arrangement where the sides of intake/exhaust are swapped around. I guess I was hoping for some direction. Has anyone here expiremented with similar arrangements? What worked best for you? Also, how did you test each configuration? Bridge test? short layer test? (like a cone or something..?
RE: Case Fans/ positive/negative pressure/best practices
My guess is that the flow (or rather lack of it, particularly turbulent flow) is more significant than the very slight differential in pressure between the enclosure and room air, when it comes to improvement in print quality from adding the enclosure.
My enclosure (3d Upfitters) draws air in through the power supply and out via a port in the rear. The flow is VERY low, and this really prevents using on-off of the flow to precisely control the temperature as I had hoped.
However, the improvement in print quality by adding the enclosure was more then enough to justify the adding of the enclosure, and I have not tried to closely control the temperature as I had originally planned.
RE:
I'll be honest, I didn't put a huge amount of thought to the fan configuration in my case simply because I followed the directions of the manufacturer.
However, I do think negative pressure might have an added benefit of making sure particles don't get blown around inside the enclosure. So less than the performance benefit, but more of a practical one? If that even tracks.
Aaron
RE: Case Fans/ positive/negative pressure/best practices
making sure particles don't get blown around inside the enclosure
like a paint booth? are there filaments that thrive in a sterile printing environment? I guess I'm all set up for that!
RE: Case Fans/ positive/negative pressure/best practices
I think dust creeps in pretty much no matter what. To what degree that really makes any difference though, I couldn't say.
Aaron