This is one of my Maya mini tutorials for beginners with, maybe, insights for pros...
Can a Ramp Cut?
Of course, it can!
And this is how it works...
Before we can cut a NURBS cylinder into two we need to create one.
Right Mouse Button: Materials > Assign New Material > Your choice
Adjust the colour to your taste and click on the mapping icon of Transparency.
Choose the Ramp.
If you're not familiar with the ramp's Attribute Editor: The activated little disc is related to the colour next to "Selected Color".
We want a sharp cut, not a soft one. So change the Interpolation from Linear to None.
Now it's slider time: Change the red colour to black, the green to white, the blue to black.
After moving the top black colour down a bit you get a picture like this.
This is what it looks like when you render the scene. A clean cut. The cylinder is transparent where the ramp is white and opaque where the ramp says: black. Let's make the cut horizontal rather than vertical.
Change the Ramp Type from V to U. And render again...
Ramps in combination with Transparency
are a powerful tool for hiding certain parts of the geometry. For the
real cut when you actually want to move one part of the object away
from the other you need conventional modeling tools.
Why is the center of the cylinder not totally black?