though most people use two plates with milled slots, we use three plates. the middle plate in our case was waterjetted with slots to hole .125" steel pin upon which the delrin wheels could spin. this technique saved used tons of time, but i realize not everyone has a waterjet.
another interesting approach was a spherical wheeled kiwi drive that we prototyped extensively but never used. trust me, it's awesome.
kiwi wheel
kiwi drive
spheres