Kerf is the amount of material removed during the cutting process along the line that is being cut. For a waterjet, the kerf is very narrow because of how thin the stream of high velocity water directed at the piece of material is. This of course depends also on nozzle size, but typically kerf tends to be between 0.020 to 0.060 inches. The narrowness of the kerf contributes to the precision of the waterjet and also decreases material wastage. Many materials are very expensive and every amount saved even if miniscule adds up.
Cut Path Offsetting
Even though the kerf on a waterjet is very narrow it is sometimes still taken into consideration when making a cut. When dealing with very precise dimensions or pieces that require a high level of accuracy the cut path will have to be offset.
Kerf compensation is the process of adjusting a toolpath to account for the amount of material removed in the cutting process. For example imagine that you want to cut out aluminum square with the dimensions of 3 inches by 3 inches. If you cut right along the vector design line then the kerf will cause the cut out square to be slightly less than 3 inches by 3 inches. By entering the width of the kerf or cutting tool into your CAD/CAM software it will automatically adjust the toolpath so that the desired dimensions are present in the final product. Therefore the tool path will be offset so it is instead on the outside of the design line. This way the square will be exactly the right dimensions. If on the other hand you want the square outline left in the material to be 3 inches by 3 inches then you will offset the toolpath to the inside of the design line. To read more about offsetting tool paths view previous blog post.