After measuring more precisely and re-testing the other belts, the difference is smaller than I thought. It appears my previous measurement of 0.0006 per kg was for some reason worse than reality. Measuring with the same setup as the Gates belt, the stretch is more like 0.00040 per kg while the gates belt is 0.00032 per kg.
It’s hard to see the construction by eye, but with enough zoom and flash from my phone camera, I can see the cords in the three belts. In the Gates belt I count 12 cords and in the other two I count 10. In no-name belt 2, they appear smaller in the picture but I’m not 100% confident that’s real. The belts with fewer/thinner cords seem to have less stiffness but I am wary of confirmation bias so I won’t draw a conclusion from that.
Anyway bottom line it looks like the difference is only about 25%, not 2x like I thought. The previous stretch measurement seems to have been somehow inflated by the way it was measured and it wasn’t as bad as 0.0006 per kg.
And yes I just placed an order recently. I’m planning to make lots more mistakes cutting steel, and many tools could die. Although it’s tough because the 4th and 5th axis are fighting for priority, so the steel might end up taking a back seat.
