CR-7 XY idler wheel holder with belt tension adjustment (皮帶緊繃件 remix from冰大)

Thanks my friend Chinpin Ko's design.
http://www.thingiverse.com/thing:1124716
http://www.thingiverse.com/thing:1094285

My improvement are:
1.Change x unit to one site screw, which can give x-axis five more mm range. (otherwise the nozzle car will be blocked)
2.For y-axis unit, I dig a hole so you can change belt more easily.
3.Using curved surface to make it smoothing.

感謝嗑清冰大大的原設計
我的改進是：
1.x緊繃件去除掉一邊螺絲固定，這樣子就可以讓x滑車不會被卡住，大約延長5mm的極限。
2.y緊繃件挖空下部，這樣可以使裝皮帶更方便。
3.設計了幾個弧角，拆裝更方便，外觀也比較好看、