There is a technology called a servo-belt which is a combination of a rack and a belt drive…
Here is how it works. https://youtu.be/OdJoVh6DRPA?t=62
It’s really clever. Here’s the link to the guy buy the guy who invented it. http://www.cnczone.com/forums/linear-and-rotary-motion/59570-forum.html
I haven’t read the patent, so I don’t know what he claims. I was thinking that it might be possible to have a MPCNC printer print out a rack that a belt could fit into..