Maybe the first thing about waterjet you want to know is “How thick can they cut?” This question is every one will ask before deciding to buy a water jet. But, the question may lead to misleading answers. Or, on the other way, it means the question is not clearly. For example, the Grand Canyon was essentially cut with an waterjet process in a way. The real answer to this question is, “How long are you willing to wait?” Cutting speed is an exponential function of thickness and type of material.
For soft materials, you can cut extremely thick pieces. For example, you can cut two foot thick (0.6 m) sponge easily.Practically speaking 2″ (5 cm) to 3″ (7.5 cm) thick steel is about the upper thickness limit for an abrasive waterjet.
If you want to cut steel that is thicker than 3″ (7.5 cm), the time to cut goes up significantly and it becomes less and less cost-effective to use a waterjet. In the case of exotic materials where the material is expensive and difficult to cut by other means, then 3″ (7.5 cm) and thicker may be practical. Titanium is an example of such a material.
It is possible to make very good money, in special cases, on materials up to 5″ (13 cm) or 6″ (15 cm) thick, but it is not recommended that your average machine shop purchase a machine with the primary purpose of cutting material thicker than 2″ (5 cm) thick.
If the cut is along a straight line, or a shallow curve, then it is also more practical to cut thick materials. However, if there are sharp corners or curves, then the cutting quickly becomes extremely slow.
While you can cut steel as thick as 9″ (23 cm) and aluminum as thick as 12″ (30 cm), this is not the norm. Parts cut from such thicknesses may take an entire day.
Note that water pump horsepower will speed up how quickly thicker material can be cut, but it doesn’t allow you to cut thicker material. Higher horsepower may make it more practical to cut thick material, however, if it reduces the cutting time enough.
article from: http://www.waterjets.org/index.php?option=com_content&task=view&id=106&Itemid=31