Timing belts

I'm building a 3ft by 4ft router. Has anybody successfully used
timing belts to control gantry movement and could you recommend a belt
type and a supplier? Should I expect backlash problems controlling
movement over a 4 ft distance? Other problems?

The belts and pulleys seem to be relatively inexpensive, it seems
relatively simple to implement, and gantry speed could be changed
easily with pulley diameter changes. How come timing belts don't seem
to be used more for cnc router control?

Mike