Hi Janne - re cogwheels, maybe something like this,

Draw one circle and one tooth:



Select the tooth and do Transform / Array / Circular:



Select the circle and all those teeth and do Construct / Boolean / Union - in MoI you can do boolean operations on curves as well as solids. This should merge all those curves together into one single larger curve:



Then Construct / Extrude:



I'm not sure if that is a correct cogwheel or not, but that might give you an idea on one possible construction method.

- Michael