2D: Cascade Elevator
Elevator Blocks
Every modern elevator will use some form of "elevator block" to allow the stages to slide past each other smoothly using bearings.
COTS Elevator Blocks
Most teams will purchase elevator blocks from WCP or TTB instead of manufacturing them in-house (because of the time investment and machining capabilities of a typical team) but elevator blocks can also be made with plates instead of billet (see 2471 2018 Robot CAD).
Reference Design
The reference design uses the WCP Inline Clamping and Inline blocks, but different blocks from WCP or TTB could be substituted with little to no design changes besides the distance between the stages on the sides.