Aluminium Framed Router

[lucan07]

Been thinking about my pulleys and how to secure them over breakfast, it may be obvious that I have little or no engineering experience so is this an acceptable way to lock pulleys securely.

My problem:
Each pulley is drilled and tapped and fitted with opposing 4mm grub screws, but motor and ballscrew shafts to which they are mounted are both round so not an ideal situation and I sure they would eventually move at some point.

My intended solution:
To drill into the pulley and shaft from the end effectively making a semi circular keyway into which I can insert a pin, I am thinking that 2-3mm drill giving 1-1.5mm semi circular key slot in both shaft and pulley would be enough to lock these connections and prevent slippage.

I know keyways tend to be slotted and have vertical sides, but as an amateur who did not consider the amounts of torque involved moving weight at speed
a) is my solution viable?
b) is 2mm or 3mm with a steel pin sufficient to do job?
c) is there a simpler way I haven't considered?