superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support  

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

 Nothing but wild guesses possible unles you post your file here. Save it from Prusaslicer's File menu (Save project as) as a 3mf file, then Zip compress it (important, or the forum software won't accept it), and attach it to a post here. 

This way we can check  other the STL and your settings. I've designed literally hundred of models in Fusion and never had an issue like the one you described. I suspect that the model may be flat but is slightly rotated, so that when it loads into PS, it is slightly tilted and not sitting flat on the sheet. But again, without the 3mf this is just a stab in the dark. 

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

hotend carriage mount

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

The bottom of your model is not flat. The slicers are indeed slicing what you have given them.

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

Not only what sylviatrilling mentioned, but I'm getting all kinds of invalid data warnings, seems like you might want to go back and look at your usage. Perhaps more realistic numbers, relative to your flatness, your out 0.39mm and your extrusion numbers aren't looking much better.

Regards

Swiss_Cheese

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

The bottom of your model is not flat.

Huh, I was right!

Click on your model, press F, then select the base of the model to put it flat on that face.

There's also the fact that Prusaslicer won't accept your perimeter extrusion width of 0.3 for a layer height of 0.3 but if you bump it to 0.4, it looks fine to me. 

Me, I would also disable Detect think walls (which can have undesired side effects and I use only if absolutely needed), change the top and bottom layers to minimum of 1 mm, and use 15% gyroid infill, which brings print time down to less than 7 hours, compared to 9+, where you started. 15% gyroid, 4 perimeters should be plenty stable for a hotend mount.

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

Thank You. I'll try all those things. I'm curious because in F360, I've tried so many ways to ensure it's flat before exporting, but still having this issue. In F360, the bottom is indeed flat, as in one selectable plane.

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

Yes, the problem is not that it's not flat, it got exported from Fusion (and then imported into PS) slightly tilted. That can happen when the model gets inadvertently rotated a tad.

If you want to zip up your .f3d file and upload it here we can take a look.

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

Thank you....turning off "detect thin walls" seems to solved it. I'll keep experimenting to find a better solution, but that worked. You guys are awesome!

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

so, even if it's become rotated, shouldn't cura add supports for that area, instead of ignoring it?

RE: superslicer and prusa slicer are both ignoring the bottom layers of my f360 model, until higher layers, then printing without any support

Probably not enough space in the gap for supports.