This picture shows the kind of printing failure that frequently results from a poorly designed cooling duct. Most of the cylinder printed fine (still tuning this printer), but the part in the wind shadow of the cooling duct was still malleable when the next layer was added, causing the layers to buckle and bulge instead of stacking properly.
I’m not sure why so many printers either come with no part cooling fan or a cooling fan that only covers part of the print, especially with printers that are designed primarily around printing PLA. A well designed part cooling design can improve print quality significantly without adding significant costs. This defects in this design however, are entirely my fault. The design is shown below, it directs two streams of air at the nozzle, at approximately 120 degrees apart. I was hoping this would be sufficient, but it still leaves a significant wind shadow, at least when printing vertical cylinders. While it is sometimes possible to fix this issue by lowering the print temperature, decreasing print speeds, or adjusting other print parameters, there are tradeoffs to fixing the problem that way and it’s better to fix the airflow. That’s why I consider the defect to be a printer failure, not a printing failure, it should should be fixed by modifying the printer, not the print parameters.
My preferred style of cooling duct is to use two high power blower fans and direct two symmetric streams of air just below the nozzle. It does a decent job of solving the issue above without blocking the view of the nozzle. I’m not sure what happens to the airflow when the two streams collide near the nozzle, probably lots of turbulence, but it works well for most of my prints. Unfortunately, space is limited on this printer and I haven’t found a good way to integrate multiple cooling fans. Below are pictures of the carriages from my RigidBot and Eustathios printers.
Work in Progress
I’m still working on a better fan duct, the latest iteration fixes the problem above by reaching out further and adding internal ribs to help direct the airflow, but this limits visibility more than I’d like. There will probably be a few more tweaks before I end up with a design that I’m happy with.