These are some intake ducts I designed for a Printrbot Simple Metal.
I don't expect much in terms of a performance increase from them - I just thought it would look cool, and act as a decent "grill" of sorts for the intake.
Personally, I prefer the one with the single support arm, but I've provided both!
My exhaust duct is from here:
Please feel free to add pictures of your "Makes"!
I suggest printing with a higher infill - at least 25% or so.
Mine was printed with a 0.15mm layer height, using the "brim" option in Cura. This required using an exacto knife to take the edges off after printing. However, it should be able to be printed on a well-prepared surface without a problem. You may still want to trim the bottom of the inside edge of the duct though.
Print with the duct facing up. No supports necessary.
When installing, you're going to want to take all the screws out, put them in the duct separate from the printer, then put the duct on with all four screws on it.
I highly recommend using a ball headed allen key. It will make it easier to not damage the duct when tightening the screws.
Also, I think an acetone vapor treatment would work wonders on one of these - that's on my list of projects.