Thanks for the reply. I wanted to change the parameters inside the scad file using OpenScad application. I used the thingiverse optimizer to generate the servo arm I wanted. Works very well.
But I still wanted a scad file to work for me. I filled in the tooth count of 21, but no preview with the 21 teeth gear. Just a gear with no teeth appeared in the display. I can change profiles by changing the numbers. ( in this case futaba -2f-21t nuber 4). No teeth.
So here is what happen today a few minutes ago. I open the scad file and changed only the profile futaba-2f-21T (number 4) and it worked!!!!
Work computer did not work correctly. But home computer worked correctly. Thank you for the reply.