In this tutorial i show you how to make the teeth for a gear using the instance command and a revolve cut. if you would like to download the models and renders for this tutorial please right click and save the zip file below from my dropbox
Good tutorial, but a couple of points/suggestions;
1) You can't have 30 teeth at 20 degrees. You could have 30 teeth at 12 degrees or 18 teeth at 20 degrees. Number of teeth x angle of separation must = 360 In your example you get 12 overlapping cuts.
2) You could apply a surface colour to your moulded part so that any cut which breaks the skin of the moulding will automatically expose the solid part colour underneath. If you had done this you will have found that the outer diameter and centre axis are not machined surfaces.
3) You could apply the rounds to the first tooth, group the touth cut and rounds and then pattern the group. - much quicker and easy to redefine number of teeth and spacing e.g. family table.
I know this is a quick tutorial and I'm being picky but I find the above good practice.