@pascal I tried to report a problem with ExtrudeCrvTapered in April 2014. ExtrudeCrvTapered - bad result Unfortunately a long and confusion discussion ensued and I think McNeel ignored my report. I don’t know if it is related to the problem in this post, but perhaps an indepth look at both ExtrudeCrvTapered and ExtrudedSrfTapered is in order. There may be a problem in the basic algorithm used.