Term "Fixed Bridge" means cast iron, at Onsrud. The term also means the spindle travels the stationary bridge along the tables’ width at the same time as the tables pass under the bridge beside their short dimension.
Design like this only occupies half of the floor space like a typical Tubular Fixed Gantry design would occupy. Machine’s design is very efficient, shuttling the twin tables for constant production and 100% cutting time. This design also permits loading and off-loading the CNC's table without stopping the cutting and production operations that are occurring on the other table. It has a heavier and thicker cast iron frame that tends to naturally absorb or dampen the cutting vibrations.
In other words, this cast iron just has a better skill to absorb and dampen cutting vibrations, while steel will tend to expand and pass on these oscillations to the rest of the frame. When you are cutting different man-made materials most of the time, a heavy , tubular steel frame like Panel Pro Series is always acceptable.