Filter outer perimeters in post processing?

I find that on overhangs, my outer perimeter tends to lift. Normally OK as the next pass pushes it back down but often the head will travel through it during other operations, damaging the finish. I want to write a post processing script that will run the extruder above these outer perimeters with no extrusion to help push it down as it cools. Not sure if it will work but thought a post processing script would be a good way to test it. The first step is figuring out how to identify what portions of the g-code are the outer perimeters. Any suggestions? Is there a verbose mode which annotates details like this?

I have doubts that it would do any good even if you manage to implement it. I have watched prints where the head has always passed back over a curl-up in a non-printing move by chance, and it has done nothing to flatten it out - if anything it makes it curl up even more. On difficult prints I usually stand by with a flat needle file and push down the curl-ups between head passes as they occur, even filing a bit off if they won't push down all the way. Lowering the extruder temperature often helps, but I suspect a better way to prevent them would be to improve the extruded filament cooling on layers that have overhangs - which may entail a mechanical modification to your printer.

My main solution however is to make my designs with only gentle or no overhangs (I realise it's not a solution when printing other people's designs). A better part can often be obtained by printing the part in sections (each section printed in the most favourable orientation), and chemically welding the parts together with a solvent glue (e.g. acetone for ABS) post-print.

Dave

i do stumble against same problem. I've found out various slicers deal with overhang better or worse and it seems key ingredent is amount of material extruded on overhang.
I think logic behind this is fact that filament coming out of nozzle needs to be 'stretched' to reach proper dimensions as layer height is lower than nozzle diameter.
This works fine as long as we have full layer underneath. If there is overhang, part of extruded thread is unsupported and instead of being stretched, it just pulls itself up .

Extruding more helps, just try i.e. increasing extrusion width in slic3r or applying modifier increasing extrusion width just on overhang part - it works wonders.
both methods have some drawbacks - one decreases overall model resolution, another creates weird artifacts as slic3r cannot deal with modifiers correctly atm (it creates them as 'separate' isles with separate settings which is kinda ok, except you get seams around them which is not always desirable)

Post-processing could work by just checking if 'current' layer has enough support underneath (comparing vs layer below), if not - just increase amount of feeded material to compensate.
I would be glad if such post-processing script existed as this would allow fixing gcodes generated in many various slicers, though i've filed bug/feature request in slic3r as native support by slicer would be also cool (one could modify more parameters , like extrusion width, extra perimeter count, speed... )

greetings