Hi DigiD, I've attached a tuned up version here which should now boolean union ok.

So what I did was deleted that little degenerate face fragment and separated out and rejoined the surrounding faces to get rid of it. Then I went around and deleted faces from all areas that had multiple coplanar pieces and remade them into single larger planes by selecting the main piece and using Construct > Planar.

Then probably most significant I remade your boolean block to just push straight through a ways into the main body like this:


Rather than trying to hug right along the curve like this (and yours was just a very slight distance apart from the main body):


Also for the cutout on top of the block I made a deeper one so that it didn't overlap right on top of the surface on the main body but is instead a little below it, so that eliminates problems from skimming intersections in that spot too:



Hope those things make sense, let me know if you need more information on why that's better.

Also another thing is when you make the STL file try making one version using the "Divide larger than" setting (applied to all faces) something like this below, that will dice up any triangles longer than the distance you put in there and that can be better than having long skinny triangles that go across a significant length of the object.



- Michael

Hi Michael

Thank you for the detailed tips and fix .

Studying your detailed commentary and there are now some more areas of MOI that I will be looking into.

Thanks also for the new STL strategies to try for Fan Duct version 4 .

Here is how version 3 the first successful prototype turned out . Bit rough ( your fix's and methods not used on this one) , but I expect the next one printed will have a better smoother finish using your recommendations. Should also benefit from the better fan cooling cooling like the finish on the new orange fan finger guards just printed

Hi DigiD, you're welcome and your print turned out quite well!

- Michael