From Cricut Hacking Wiki
Why hack the Cricut?
Well, while it's true that there are plenty of craft paper/vinyl cutters out there that let you use them however you want, Cricut cutters are pretty easy to come by. You can also pick up parts and cutters at a typical craft store or even a Wal-mart. Many people also let their old units go for next to nothing once they upgrade to the latest version of the Cricut, meaning you can pick one up cheap pretty easily. Also, there's already commercial software out there that will let you cut anything you want on a Cricut, without modifying the firmware, so it doesn't seem to be any technical reason why you can't hack the thing.
Currently, we're figuring out the details of how to control the Cricut from a PC. Once we get that working we'll see where we go from there...
Help document model behavioral differences Cricut Cutting Standard.
On going Research
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