Hi Brian, I'd do something like this:

Start with one tooth which is slightly narrowed from the other gear, and draw a line off of one part of it. Then do a Transform / Array / Dir, and pick the 2 points as indicated here:



That will create this:



You may need to adjust the length of that line hanging off to the side, I made it a bit shorter or longer until I got a nice fit. It looks like you have the equivalent of a rather long line in yours.

Then you can repeat the array dir, but reversing the order of the points to do an array to the other side, then add one extra little line and then that straight part can be closed off and finished:



- Michael