Support Interface Layers only every other layer.  

RE: Support Interface Layers only every other layer.

I'm afraid without a saved project file (File>Save project as) that we cant really answer your questions.  With the project we can see exactly what you are slicing as the .3mf file contains not only the model but all of your settings, modifiers, orientations etc.  So slicing should give the exact same results and we can then see and rotate, go through the layer previews etc.

RE: Support Interface Layers only every other layer.

3MF file

Thanks for the quick reply. I attached an example.

RE: Support Interface Layers only every other layer.

That support looks perfectly normal for PS.  Which is to say its not that great.  Support layers and their thickness is totally independent of the layers used on the model itself (unless you enable Synchronize with object layers).  Next version due out (2.4) is supposed to have improvements for support in there.  Its one of PS weaknesses which is why many are looking forward to seeing what the next release brings us.

The layers for the interface look normal but whatever you set you wont get good looking bottoms on your parts above supports with the current release.  

The other support settings you are using are also problematic.  Anything less than a contact distance of 0.2 will weld the support to the part making removal difficult.  Unless you have a MMU with soluble supports and a contact distance of 0 that is.  Also you have painted support enforcers on but then have supports set to everywhere which ignore the enforcers.  Even there you have far far too much painted with enforcers than you actually need.  Only the very tops actually need any support at all with this model. 

The bridging perimeters are also sliced at the nozzle diameter/extrusion width so that is leading to very thick layers on those areas anyway and not your layer height which is normal for PS.  Its one of the reasons that the support interface is actually placed so far away from the model. Unless your printers cooling sucks I'd be tempted to actually turn off bridge detection.  

I've attached a project with how I would try printing it.  I've tweaked quite a few settings to try and keep the speed/flow of plastic even which helps with keeping things the same.  Basically a few speeds as well as minimum layer time on the filament profile.  Also adjusted the support settings and painted on enforcers.  

Hopefully its of some use to you.

RE: Support Interface Layers only every other layer.

Wow, thank you so much! Everything you say makes perfect sense and I will try to slice and print with your settings. The only thing I didn't understand is what "Detect bridging perimeters" does (wrong) in combination with support. Maybe you could elaborate on that point?

The cooling on my very new printer (Mk3S+) seems to be much better than on my trusty but now retired Mk2.

I also looked at the other settings you changed and saw that you reduced "Slice gap closing radius" to 1/10 of the original setting. Is this a general recommendation of yours, or does it also have to do with supports?

Thanks again, I very much appreciate your help!

A general remark: While generated supports might not (yet!) be the best, I'm using Slic3r/PrusaSlicer for a long time now and  for a FOSS product it's very polished and a joy to use. And I'm very happy that Prusa Research adopted Slic3r instead of building their own proprietary and closed product.

RE: Support Interface Layers only every other layer.

With bridging/overhang perimeters (the ones colour coded as dark blue on the preview) because they are not printed against any layer below Slicer makes the assumption that the cross section is going to be the width extruded from the nozzle.  So with your 0.6mm nozzle it assumes that part of the perimeter is going to be 0.6mm thick (actually I think its the extrusion width so 0.65 from your setting iirc).  On an actual bridged part where the strand is going from point A to B directly in a nice straight line and is anchored at both ends this mostly works but even then the underside of bridges are not pretty.  With just overhangs that curve like on your model you have to accept that they will droop a bit until they hit the support anyway and if they are going to do that you might as well just extrude a 'normal' amount of plastic for a 0.2m or whatever layer.   I find in practice it ends up looking a bit better in many (but not all cases).
Unfortunately you have to turn off bridge detection to do that so it doesn't extrude these thick perimeters.  Although rumour has it that there's going to be an option for that in the next release.

The slice gap closing radius is unrelated to anything on that model.  Its a general setting change I make.  There are some of the tolerance test models where the slicer was actually removing the tolerance gap and 'filling' it in when set at 0.049.  Its also caused issues in the past with print in place mechanisms like hinges or flexi models.  Adding an extra zero is just the easiest to type in 🙂
Its there to try and help 'fix' bad models that have holes in them.  If a model is that bad then I don't want to print it or I will fix it anyway. 
I usually check anything I download for errors and look at its cross section to spot potential problem areas and thin sections before hand. 
Its why I normally turn off thin wall detection too.  As that setting can also cause its own issues.  If a wall is too thin to print normally then the model should be adjusted rather than using an algorithms best guess.

I agree that PS is the best of all the offerings, its why I use it.  It does have areas where its weaker than others though, that's just an objective opinion.  Supports being one of them.  Given the amount of development though I'm sure any areas where it lags will (eventually) be addressed.