There are two limits about max thickness. One is practical limit, the other one is physical limit.
The practical limit means for most materials, the condition is about 100mm thick. If the metal thicker than that thickness, the tolerances will be dropped and the machining time will be increased. For some projects, like cutting titanium, the waste metal has the great profits. According to APW customers’ report, the thick at 100mm is appropriate.
The physical limit means the maximum Z-axis travel. For most APW machines, it is around 150cm. But the Z-axis travel can be extended if you want to install a longer size.
article from: http://waterjetapw.com