Rhino 3D Help Forums

Hello,

I need some help, I started with the tutorial "modelling a wind-up clock"
It`s really a nice tutorial, I learned many new functions
but already ond the 2nd page there is a feature/command  I cannot achieve

"Next thing would be to join those surfaces together with BooleanUnion command. Then, using Sphere command, create one sphere with 1 unit as radius and position it in the center of the screw looking from Right viewport, and move it a bit to the right from either top or front viewport. To do that small move, turn off the Snap option.

Using BooleanDifference command you need to get something like on the image 22, but before you do, you need to cut the sphere into half so you can flip the normals."

It`s the part with the BooleanDifference. I cannot get the result like in the image 22.
I cut the sphere into half   but I don`t understand what is meant by   "flip the normals"
When I`m using the booleandifference I get always a hole in the sphere  indstead of the sphere passed to the planar circle  /circular plane.

Sorry for my english, anyway, I hope you anderstand my problem

Thank You      :)

I have answered your question in your email, but just in case some one else gets into the problems, I will answer it here.

The command for flipping the normals is FLIP. It will first show you the normals' direction, then if you like you can change the direction.
When using Boolean operations, usually you are using them on two objects. So when doing BooleanDifference, you are actually cutting one object with another. In this particular command, the first object that is selected is the cutting object, and the second one you select is the object you want to cut.
So, here comes the problem for our little Rhino. Lets say you wish to cut the cylinder in half with you semi sphere. How on earth our little poor Rhino can possibly know which end of the cylinder to keep and which to delete. Well, that is where normals come in.

Where the normals are, that part will get deleted, and vice versa. One suggestion, you can always use Boolean2Objects command which lets you cycle through all Boolean operations and variants, you just choose which one you need. Actually that would be my suggestion to use if you are not so good with Booleans and understanding our good friend George Boole ;)