I copied the design for this box joint jig from the great http://woodgears.ca/.
The carriage and rails use maple for the sliding parts. No oil necessary.
I tried a few joints before building the spring-wheel assembly, which is itself box-jointed. My carriage only had a little play with no spring but I decided the spring is necessary to keep things aligned.
This is the first gear-drive I've tried to make and turned out to work pretty well.