I was able to ake this work
(setq INSPT (polar REFCORNER REFANGLE LEN)
BOX (vlax-invoke SPC 'ADDBOX INSPT 240 240 360)
;;; SEL (ssget '((0 . "3DSOLID")))
WALL (car (entsel "\nPick wall: "))
wall (vlax-ename->vla-object wall)
;;; (vla-boolean WALL acintersection BOX)
WALLPIECE (vla-boolean wall acsubtraction box)
)
but I thought that the acintersection created a new piece of 3dsolid, not erase everything but the intersection