Big  Blue Saw



How close can a hole be to the edge of a waterjet cut part?

We know that there are limits to hole size and narrow areas are a bad idea but how close can you place the cutting line of a hole and another feature? In some cases placing the holes too close to the outer cutting line can cause problems. We can make some assumptions based on the known accuracy of the waterjet cutter, but it's best to test it out.

In this design for our test, the 6 holes are 0.12 inches in diameter, and are placed progressively closer to the edge as you go further to the right. The holes are situated 0.09", 0.06", 0.04", 0.025", 0.01", and 0.001" from the edge. To see how the stock thickness affects the resulting parts, we waterjet cut this part from aluminum 6061 in three  thicknesses: 0.063", 0.125", and 0.25".

First up is the 0.063 inch thick material. Here's the result:

Notice that the hole closest to the edge (0.001 inch) is starting to wear through to the outer cutting line. Keep in mind that holes are only guaranteed to be within 0.01 inches of the specified diameter due to nozzle wear and other factors. Also, the thin section between the hole and the outer cutting line can vibrate during cutting, again leading to this kind of blowout.

In the photos above, you can just barely see that the hole spaced 0.01 inches from the edge is starting to cut through to the edge as well.

The effect is more pronounced in the 0.125 inch thick material:

And it's even more visible on the 0.25 inch thick material shown in the two pictures below.

Remember that due to taper, the hole is wider on the top face, and narrower on the bottom face.  (Low-taper waterjet cutting wouldn't help in this case. The taper-compensation process needs a certain amount of space to work correctly, so you will still end up with taper on small holes even when cutting using the low-taper option.)

If this kind of defect doesn't matter for your design, we can still cut the holes close to the outer cut line. Just keep in mind that your holes might end up connecting to the outside if there's not 0.025 inches or more between the hole and the outside of the part.