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You've just received your parts from Big Blue Saw. You've got some sharp inside corners, but the waterjet rounded them off! You could take a file to the parts to get rid of the excess, but who has time for that? Read on for hints on how to clear the corners so you never have to face this problem again.

When the waterjet cuts, it will come up just short of the inside corner. This is due to the cutting diameter (kerf) of the waterjet stream. Remember that the waterjet stream is round, and can't reach a sharp inside corner. Read more about that in our article on the limitations of waterjet cutting. The rectangle on the right in the image below shows rounding of the inside corners on 1/4 inch thick waterjet cut aluminum.

Many designers will remove some extra material to make sure that the inside corner gets removed. The most obvious way to do that is by putting an arc centered on the corner.


Taking a closer look, you'll notice that the arc has a diameter of just over 0.07 inches. This is so that the waterjet can enter the corner area through an opening that's 0.05 inches wide. We recommend at least an 0.05 inch opening to make sure that the waterjet controller software is able to identify an open area which the cutting stream can reach.

Here's the result of this type of corner clearance.

You'll notice with this that with this design we're cutting away a lot more material than is truly necessary. There are other ways that don't remove quite so much material.

If we simply extend the cut away from the long side, with an arc with a diameter of 0.05 inches, we get something like the shape shown below. (I've heard this referred to as "Finn ears" because it resembles the hat of one of the characters on the Adventure Time cartoon.)


Here the arc is 180 degrees and ends on the original corner.

Another way to go about the same thing: put the arc on the short side.





But we could still remove even less material and still snip away that annoying corner. If you create a 180 degree arc with an 0.05" diameter which passes through the original corner, and ends about 0.0354 inches from the corner. See the diagram below.

The result is a rectangle with much less excess material removed near the corner than with any of the other corner clearing methods.

The result is what's shown in the images below.


This corner cutting method gives the best lookng results and removes the least material. One potential disadvantage is that you might need one of the sides to be fully straight all the way into the corner for strength or stability.

To test these designs out, I waterjet cut a tab piece from 0.25 inch thick aluminum. It fits well into any of the slots cut with the corner removal techniques listed above.


Have a favorite corner clearing shape? Let us  know in the comments.

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