Something to be aware of....place an indicator on the axis that is controlled by the long belt. Place your finger in the middle of the belt, and press downward (or pull upward). Note how much the indicator moves. Now, 0.004mm (or even 0.1mm) most likely seems like a small drop in a large pool. The belt will most likely spring up and down during use. What's really entertaining is when the programmed axis motion hits the resonance frequency of the belt, and it REALLY starts vibrating like a plucked guitar string. Springing can cause all sorts of unwanted issues. Cut quality being one of them. On long stretches of belting, it really helps to have tracks for the belt to lay in, to eliminate the springing. I'm not trying to be a "negative Nancy", just pointing out something to keep an eye on.