this looks like a horrible and unnecessary dense surface.
_extendSrf fails here as well (8.16 on a mac)
_untrimAll
Keeptrims = yes
will show the underlaying surface and the trim-curves (blue)
the first
_offsetCrvOnSrf
8mm
the second offset is
30mm
I recommend the following workflow
_untrimAll (keep trims), _offsetCrvOnSrf _trim
instead of extendSrf.
There where some issues with extendSrf.
One is fixed in the current service release candidate.
ok - but i tested at least on a mac and it does not do the job as you asked - see above.
EDIT:
_extendSrf - click the edge, enter -8 (MINUS EIGHT) works here.
and
_untrimAll (keepTrims)
_dir (flip) the trim curves
_trim
_exendSrf 8 (without Minus) does the job as well.
did you try -8 ? does it work
kind regards - tom