Spur Gear size control

[sgreco]

Are you using Inventor's design accelerator to make the spur gears? I just assume this based on the description of your situation.

If so I would recommend not. I have tried it before and it is confusing to work with and easier to just draw the gear yourself.

Unless you plan to make your own gears (in which case you can do whatever you want), I just create one of the teeth and circular pattern it around the part. Copy geometry from a gear you find from a vendor of gears.

If you're in SolidWorks or ProE you have to draw them yourself anyway...which is for the better since in my opinion it is an easier way to make a gear.