I ordered a 20 degree cutter. 20 degrees seems the mostly likely angle.

Today I just happened to be using some epoxy putty for another project &
I had a little left over. So I rolled the gear in it, to get a rack &
measure it. Even though the putty was stiffer than plasticine and set
up hard, it was not ideal. It tended to deform some from the perfect
rack that it was supposed to be.

Here is a photo of the molded epoxy, ground flat on one side & with
straight lines fitted to the profile:
http://imgur.com/a/ixovG
Right-leaning lines are 18-19-19-20 degrees and left leaning ones 14
(all). Inconclusive, although closer to 14.5 on average.

Bob