Written by Techni’s Service Staff
Waterjet cutting is unique in many ways. One unique characteristic it that the Kerf width is dynamic in nature and can be affected by changes in any of the cutting parameters. By understanding the effect on kerf these changes make will help you produce more accurate parts.
1) Increasing garnet flow will increase the kerf width, (and decreasing reduces it)
2) Decreasing the cutting speed (or improving the finish) increases the kerf width, (and decreasing reduces it)
3) Increasing the standoff distance will tend to decrease the kerf on hard materials, but increase it on soft materials.
4) Increase in pressure will not greatly affect the kerf at the top of the part, but will reduce taper, and therefore could be important when fitting parts together.
5) Holes and radii are often cut slower than the rest of the job, so they will tend to have a greater kerf, this can also be exaggerated by the fact that the kerf tends to flare around tight radii.
6) Depending on where you measure the part, the kerf changes due to the taper affect.
7) Softer materials tend to have a larger kerf than hard material.
8) A worn focusing tube or inefficient cutting head set up will affect the kerf. It will also quite probably cause the kerf to vary considerably, depending on which direction you are cutting in. An increase in kerf width will reduce the outside dimensions of a part and increase the internal dimensions of a part. Thin materials tend to measure less kerf because you always measure at the bottom of the taper. What all this means is that if you want to cut a very accurate part it is essential that you use a new (or relatively new) focusing tube, and ensure your cutting head is running cold. Then do a test, with the exact parameters you will use on the final part and then set the kerf compensation accordingly.
A simple way to do this is to cut a straight line at exactly the same parameters you will use on the finished parts. Then use a set of feeler gauges to determine the Kerf width. Remember that the Kerf will vary from top to bottom, so only go in to the point you plan to measure the finished part at.