union problem

i can't figure out why i have problem with those vertical line that remain after UNION command.

stepenice 3D.dwg

its because the solids are not in line with the bigger solid.try to look at the attached image and inspect your drawing closely.

i see (i check all corners but i've missed this one).

on the other hand i don't know why i miss point since object snap is on (and there is no other points to attract ) when i try to attach one object to another.

if i zoom all the way i see i have gap (few micron) between objects but i can't attach them for i'm to close so i can't see cursor.