Here is a method I often use to cut keyways. The cutter is a carbide parting insert brazed to the end of a piece of HSS bar. Cut depth is a fairly conservative 0.05mm (0.002") per pass as I wasn't sure how hard the gears were. It tuned out that they were pretty soft so I could have easily used twice the cut depth.
The gears are part of a dry sump oil pump I am building. I cheated and used gears out of VW Beetle oil pumps rather than making my own.
The lathe is a Colchester Triumph 2000 retrofitted with EMC.
