Need Help!- Axis movement speed adjusted by pressure sensor

[Viesturs]

hi!

i've been trying to search these forums, but without any luck in finding an answer.

i would like to construct CNC machine that would use diamond wire to cut granite stones in slabs.

the idea is to have pretty simple design with 2 axis - X axis - move back and forth and Y axis - move the wire up and down and do the cutting during downward movement.

my problem is that i do no know, how can i build it in a way that speed of this downward movement (when the cutting is conducted) is adjusted by the tension of diamond wire? what kind of pressure sensor should i use and how can i integrate it with a motor controller so that movement speed on one axis is adjusted so that tension of wire does not exceed certain limit?

those stones to be cut are very different sizes, so determining one certain speed that would work for all in more or less efficient way is unreal