It can also be quite hazardous to use a CNC manually, as I learned the other day. I needed to run a 1/8" hole through a shaft crosswise. The CNC would be a great choice to indicate the center of the shaft and drill a straight hole, right? Well, the problem is that you don't have any feedback if something is going wrong. The CNC will go where you tell it with about a ton of force.
I grabbed a center drill from my business partner's toolbox, because it was close at hand. I put it in the toolholder and brought the machine to the correct spot. With a careful 0.001" per click of the hand wheel, I brought the tool down to the work.
Hmm, why is it not making any chips? Let's lean in and take a closer look. BOOOM! The center drill exploded and sent a piece of hot shrapnel into my lip. (Yes Mom, I was wearing my safety glasses...) Turns out that center drill was so dull that it wouldn't even have cut butter.
Lesson learned! Make sure you have a sharp tool if you're cutting something with a CNC, especially by hand! Wear your glasses boys and girls!