[mactec54]

Saying that belts only stretch unless overloaded is incorrect. Same with tooth deflection. Any load at all will cause tooth deflection and belt stretch, it's just a question of how much. Everything in this universe deflects with any amount of pressure. If you place a grain of rice on the corner of a 12 inch thick chunk of granite, the granite bends. There is no such thing as "no deflection". Tooth deflection and belt stretch is proportional to belt width. The fact that you say things like "there will be no stretch" makes me think you don't understand these facts. There will always be stretch and tooth deflection. The goal is to reduce it as much as possible. There is no point where it's eliminated completely. It's the laws of physics

And once again, the 50mm may very well be overkill and beyond what's going to give significant improvent, but I definitely dont believe there's no reason to go bigger than 16mm. The more deflection there is, the worse chatter will be during machining.

If you place a grain of rice on the corner of a 12 inch thick chunk of granite, the granite bends that's just to funny to make a comment (nuts)

It's all about Design once a Belt has been correctly Tensioned to the manufactures spec's it does not stretch anymore unless the load exceeds the spec's you obvious have not put/used any design spec's for your belt and just gone bigger is better

First you need an understanding of physics before you make those quotes

I'm sure what ever you end up with it will be perfect